HTTP Live Streaming 2nd Edition
draft-pantos-hls-rfc8216bis-12
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Roger Pantos | ||
| Last updated | 2022-11-11 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-pantos-hls-rfc8216bis-12
Informational R. Pantos, Ed.
Internet-Draft Apple Inc.
Obsoletes: 8216 (if approved) 8 November 2022
Intended status: Informational
Expires: 12 May 2023
HTTP Live Streaming 2nd Edition
draft-pantos-hls-rfc8216bis-12
Abstract
This document obsoletes RFC 8216. It describes a protocol for
transferring unbounded streams of multimedia data. It specifies the
data format of the files and the actions to be taken by the server
(sender) and the clients (receivers) of the streams. It describes
version 10 of this protocol.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 12 May 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
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This document may not be modified, and derivative works of it may not
be created, except to format it for publication as an RFC or to
translate it into languages other than English.
This Informational Internet Draft is submitted as an RFC Editor
Contribution and/or non-IETF Document (not as a Contribution, IETF
Contribution, nor IETF Document) in accordance with BCP 78 and BCP
79.
Table of Contents
1. Introduction to HTTP Live Streaming . . . . . . . . . . . . . 4
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Media Segments . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Supported Media Segment Formats . . . . . . . . . . . . . 7
3.1.1. MPEG-2 Transport Streams . . . . . . . . . . . . . . 7
3.1.2. Fragmented MPEG-4 . . . . . . . . . . . . . . . . . . 7
3.1.3. Packed Audio . . . . . . . . . . . . . . . . . . . . 9
3.1.4. WebVTT . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.5. IMSC Subtitles . . . . . . . . . . . . . . . . . . . 10
3.2. Partial Segments . . . . . . . . . . . . . . . . . . . . 10
4. Playlists . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Definition of a Playlist . . . . . . . . . . . . . . . . 12
4.2. Attribute Lists . . . . . . . . . . . . . . . . . . . . . 13
4.3. Variable Substitution . . . . . . . . . . . . . . . . . . 14
4.4. Playlist Tags . . . . . . . . . . . . . . . . . . . . . . 15
4.4.1. Basic Tags . . . . . . . . . . . . . . . . . . . . . 15
4.4.1.1. EXTM3U . . . . . . . . . . . . . . . . . . . . . 15
4.4.1.2. EXT-X-VERSION . . . . . . . . . . . . . . . . . . 15
4.4.2. Media or Multivariant Playlist Tags . . . . . . . . . 16
4.4.2.1. EXT-X-INDEPENDENT-SEGMENTS . . . . . . . . . . . 16
4.4.2.2. EXT-X-START . . . . . . . . . . . . . . . . . . . 16
4.4.2.3. EXT-X-DEFINE . . . . . . . . . . . . . . . . . . 17
4.4.3. Media Playlist Tags . . . . . . . . . . . . . . . . . 18
4.4.3.1. EXT-X-TARGETDURATION . . . . . . . . . . . . . . 18
4.4.3.2. EXT-X-MEDIA-SEQUENCE . . . . . . . . . . . . . . 18
4.4.3.3. EXT-X-DISCONTINUITY-SEQUENCE . . . . . . . . . . 19
4.4.3.4. EXT-X-ENDLIST . . . . . . . . . . . . . . . . . . 20
4.4.3.5. EXT-X-PLAYLIST-TYPE . . . . . . . . . . . . . . . 20
4.4.3.6. EXT-X-I-FRAMES-ONLY . . . . . . . . . . . . . . . 20
4.4.3.7. EXT-X-PART-INF . . . . . . . . . . . . . . . . . 21
4.4.3.8. EXT-X-SERVER-CONTROL . . . . . . . . . . . . . . 21
4.4.4. Media Segment Tags . . . . . . . . . . . . . . . . . 23
4.4.4.1. EXTINF . . . . . . . . . . . . . . . . . . . . . 23
4.4.4.2. EXT-X-BYTERANGE . . . . . . . . . . . . . . . . . 23
4.4.4.3. EXT-X-DISCONTINUITY . . . . . . . . . . . . . . . 24
4.4.4.4. EXT-X-KEY . . . . . . . . . . . . . . . . . . . . 24
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4.4.4.5. EXT-X-MAP . . . . . . . . . . . . . . . . . . . . 26
4.4.4.6. EXT-X-PROGRAM-DATE-TIME . . . . . . . . . . . . . 27
4.4.4.7. EXT-X-GAP . . . . . . . . . . . . . . . . . . . . 28
4.4.4.8. EXT-X-BITRATE . . . . . . . . . . . . . . . . . . 28
4.4.4.9. EXT-X-PART . . . . . . . . . . . . . . . . . . . 28
4.4.5. Media Metadata Tags . . . . . . . . . . . . . . . . . 29
4.4.5.1. EXT-X-DATERANGE . . . . . . . . . . . . . . . . . 30
4.4.5.1.1. Mapping SCTE-35 into EXT-X-DATERANGE . . . . 32
4.4.5.2. EXT-X-SKIP . . . . . . . . . . . . . . . . . . . 34
4.4.5.3. EXT-X-PRELOAD-HINT . . . . . . . . . . . . . . . 35
4.4.5.4. EXT-X-RENDITION-REPORT . . . . . . . . . . . . . 36
4.4.6. Multivariant Playlist Tags . . . . . . . . . . . . . 37
4.4.6.1. EXT-X-MEDIA . . . . . . . . . . . . . . . . . . . 37
4.4.6.1.1. Rendition Groups . . . . . . . . . . . . . . 41
4.4.6.2. EXT-X-STREAM-INF . . . . . . . . . . . . . . . . 41
4.4.6.2.1. Alternative Renditions . . . . . . . . . . . 48
4.4.6.3. EXT-X-I-FRAME-STREAM-INF . . . . . . . . . . . . 49
4.4.6.4. EXT-X-SESSION-DATA . . . . . . . . . . . . . . . 49
4.4.6.5. EXT-X-SESSION-KEY . . . . . . . . . . . . . . . . 50
4.4.6.6. EXT-X-CONTENT-STEERING . . . . . . . . . . . . . 51
5. Key Files . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.1. Structure of Key Files . . . . . . . . . . . . . . . . . 52
5.2. IV for AES-128 . . . . . . . . . . . . . . . . . . . . . 52
6. Client/Server Responsibilities . . . . . . . . . . . . . . . 52
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 52
6.2. Server Responsibilities . . . . . . . . . . . . . . . . . 52
6.2.1. General Server Responsibilities . . . . . . . . . . . 52
6.2.2. Live Playlists . . . . . . . . . . . . . . . . . . . 56
6.2.3. Encrypting Media Segments . . . . . . . . . . . . . . 57
6.2.4. Providing Variant Streams . . . . . . . . . . . . . . 58
6.2.5. Delivery Directives Interface . . . . . . . . . . . . 60
6.2.5.1. Playlist Delta Updates . . . . . . . . . . . . . 60
6.2.5.2. Blocking Playlist Reload . . . . . . . . . . . . 61
6.2.6. Providing Preload Hints . . . . . . . . . . . . . . . 62
6.3. Client Responsibilities . . . . . . . . . . . . . . . . . 63
6.3.1. General Client Responsibilities . . . . . . . . . . . 63
6.3.2. Loading the Media Playlist File . . . . . . . . . . . 64
6.3.3. Playing the Media Playlist File . . . . . . . . . . . 65
6.3.4. Reloading the Media Playlist File . . . . . . . . . . 66
6.3.5. Determining the Next Segment to Load . . . . . . . . 67
6.3.6. Decrypting Encrypted Media Segments . . . . . . . . . 67
6.3.7. Requesting Playlist Delta Updates . . . . . . . . . . 68
6.3.8. Issuing Blocking Requests . . . . . . . . . . . . . . 69
7. Content Steering . . . . . . . . . . . . . . . . . . . . . . 70
7.1. Steering Manifest . . . . . . . . . . . . . . . . . . . . 70
7.2. Pathway Cloning . . . . . . . . . . . . . . . . . . . . . 71
7.3. Steering Query Parameters . . . . . . . . . . . . . . . . 73
7.4. Steering Client Responsibilities . . . . . . . . . . . . 74
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8. Protocol Version Compatibility . . . . . . . . . . . . . . . 75
9. Playlist Examples . . . . . . . . . . . . . . . . . . . . . . 77
9.1. Simple Media Playlist . . . . . . . . . . . . . . . . . . 77
9.2. Live Media Playlist Using HTTPS . . . . . . . . . . . . . 77
9.3. Playlist with Encrypted Media Segments . . . . . . . . . 77
9.4. Multivariant Playlist . . . . . . . . . . . . . . . . . . 78
9.5. Multivariant Playlist with I-Frames . . . . . . . . . . . 78
9.6. Multivariant Playlist with Alternative Audio . . . . . . 79
9.7. Multivariant Playlist with Alternative Video . . . . . . 79
9.8. Session Data in a Multivariant Playlist . . . . . . . . . 80
9.9. CHARACTERISTICS Attribute Containing Multiple
Characteristics . . . . . . . . . . . . . . . . . . . . 80
9.10. EXT-X-DATERANGE Carrying SCTE-35 Tags . . . . . . . . . . 81
9.11. Low-Latency Playlist . . . . . . . . . . . . . . . . . . 81
9.12. Content Steering Playlist and Manifest . . . . . . . . . 82
9.13. Content Steering Manifest with Pathway Clone . . . . . . 83
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 84
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 85
11.1. vnd.apple.mpegurl . . . . . . . . . . . . . . . . . . . 85
11.2. vnd.apple.steering-list . . . . . . . . . . . . . . . . 86
12. Security Considerations . . . . . . . . . . . . . . . . . . . 87
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 88
13.1. Normative References . . . . . . . . . . . . . . . . . . 88
13.2. Informative References . . . . . . . . . . . . . . . . . 92
Appendix A. Changes from RFC 8216 . . . . . . . . . . . . . . . 92
Appendix B. Server Configuration Profiles . . . . . . . . . . . 94
B.1. Low-Latency Server Configuration Profile . . . . . . . . 94
Appendix C. Low-Latency CDN Tune-in . . . . . . . . . . . . . . 96
Appendix D. Interstitials . . . . . . . . . . . . . . . . . . . 97
D.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 97
D.2. EXT-X-DATERANGE Schema for Interstitials . . . . . . . . 98
D.3. Interstitial query parameters . . . . . . . . . . . . . . 101
D.4. Client Behavior . . . . . . . . . . . . . . . . . . . . . 101
D.5. Example: Interstitial EXT-X-DATERANGE . . . . . . . . . . 102
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 102
1. Introduction to HTTP Live Streaming
HTTP Live Streaming provides a reliable, cost-effective means of
delivering continuous and long-form video over the Internet. It
allows a receiver to adapt the bit rate of the media to the current
network conditions in order to maintain uninterrupted playback at the
best possible quality. It supports interstitial content boundaries.
It provides a flexible framework for media encryption. It can
efficiently offer multiple renditions of the same content, such as
audio translations. It offers compatibility with large-scale HTTP
caching infrastructure to support delivery to large audiences. It
supports low-latency playback at scale.
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Since its first draft publication in 2009, HTTP Live Streaming has
been implemented and deployed by a wide array of content producers,
tools vendors, distributors, and device manufacturers. In the
subsequent ten years the protocol has been refined by extensive
review and discussion with a variety of media streaming implementors.
The purpose of this document is to facilitate interoperability
between HTTP Live Streaming implementations by describing the media
transmission protocol. Using this protocol, a client can receive a
continuous stream of media from a server for concurrent presentation.
This document describes version 10 of the protocol.
2. Overview
A multimedia presentation is specified by a Uniform Resource
Identifier (URI) [RFC3986] to a Playlist.
A Playlist is either a Media Playlist or a Multivariant Playlist.
Both are UTF-8 text files containing URIs and descriptive tags.
A Media Playlist contains a list of Media Segments, which, when
played sequentially, will play the multimedia presentation.
Here is an example of a Media Playlist:
#EXTM3U
#EXT-X-TARGETDURATION:10
#EXTINF:9.009,
http://media.example.com/first.ts
#EXTINF:9.009,
http://media.example.com/second.ts
#EXTINF:3.003,
http://media.example.com/third.ts
The first line is the format identifier tag #EXTM3U. The line
containing #EXT-X-TARGETDURATION says that all Media Segments will be
10 seconds long or less. Then, three Media Segments are declared.
The first and second are 9.009 seconds long; the third is 3.003
seconds.
To play this Playlist, the client first downloads it and then
downloads and plays each Media Segment declared within it. The
client reloads the Playlist as described in this document to discover
any added segments. Data SHOULD be carried over HTTP [RFC7230], but,
in general, a URI can specify any protocol that can reliably transfer
the specified resource on demand.
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A more complex presentation can be described by a Multivariant
Playlist. A Multivariant Playlist provides a set of Variant Streams,
each of which describes a different version of the same content.
Earlier drafts used a different term (see Appendix A).
A Variant Stream includes a Media Playlist that specifies media
encoded at a particular bit rate, in a particular format, and at a
particular resolution for media containing video.
A Variant Stream can also specify a set of Renditions. Renditions
are alternate versions of the content, such as audio produced in
different languages or video recorded from different camera angles.
Clients should switch between different Variant Streams to adapt to
network conditions. Clients should choose Renditions based on user
preferences.
Certain streams can be played in Low-Latency Mode. Low-Latency Mode
refers to the combined use of Partial Segments, Blocking Playlist
Reload and preload hinting to enable playback at a reduced delay from
live.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Media Segments
A Media Playlist contains a series of Media Segments that make up the
overall presentation. A Media Segment is specified by a URI and
optionally a byte range.
The duration of each Media Segment is indicated in the Media Playlist
by its EXTINF tag (Section 4.4.4.1).
Each segment in a Media Playlist has a unique integer Media Sequence
Number. The Media Sequence Number of the first segment in the Media
Playlist is either 0 or declared in the Playlist (Section 4.4.3.2).
The Media Sequence Number of every other segment is equal to the
Media Sequence Number of the segment that precedes it plus one.
Each Media Segment MUST carry the continuation of the encoded
bitstream from the end of the segment with the previous Media
Sequence Number, where values in a series such as timestamps and
Continuity Counters MUST continue uninterrupted. The only exceptions
are the first Media Segment ever to appear in a Media Playlist and
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Media Segments that are explicitly signaled as discontinuities
(Section 4.4.4.3). Unmarked media discontinuities can trigger
playback errors.
Any Media Segment that contains video SHOULD include enough
information to initialize a video decoder and decode a continuous set
of frames that includes the final frame in the Segment; network
efficiency is optimized if there is enough information in the Segment
to decode all frames in the Segment. For example, any Media Segment
containing H.264 video SHOULD contain an Instantaneous Decoding
Refresh (IDR); frames prior to the first IDR will be downloaded but
possibly discarded.
3.1. Supported Media Segment Formats
All Media Segments MUST be in a format described in this section.
Transport of other media file formats is not defined.
Some media formats require a common sequence of bytes to initialize a
parser before a Media Segment can be parsed. This format-specific
sequence is called the Media Initialization Section. The Media
Initialization Section can be specified by an EXT-X-MAP tag
(Section 4.4.4.5). The Media Initialization Section MUST NOT contain
sample data.
3.1.1. MPEG-2 Transport Streams
MPEG-2 Transport Streams are specified by [ISO_13818].
The Media Initialization Section of an MPEG-2 Transport Stream
Segment is a Program Association Table (PAT) followed by a Program
Map Table (PMT).
Transport Stream Segments MUST contain a single MPEG-2 Program;
playback of Multi-Program Transport Streams is not defined. Each
Transport Stream Segment MUST contain a PAT and a PMT, or have an
EXT-X-MAP tag (Section 4.4.4.5) applied to it. The first two
Transport Stream packets in a Segment without an EXT-X-MAP tag SHOULD
be a PAT and a PMT.
3.1.2. Fragmented MPEG-4
MPEG-4 Fragments are specified by the ISO Base Media File Format
[ISOBMFF]. Unlike regular MPEG-4 files that have a Movie Box
('moov') that contains sample tables and a Media Data Box ('mdat')
containing the corresponding samples, an MPEG-4 Fragment consists of
a Movie Fragment Box ('moof') containing a subset of the sample table
and a Media Data Box containing those samples. Use of MPEG-4
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Fragments does require a Movie Box for initialization, but that Movie
Box contains only non-sample-specific information such as track and
sample descriptions.
A Fragmented MPEG-4 (fMP4) Segment is a "segment" as defined by
Section 3 of [ISOBMFF], including the constraints on Media Data Boxes
in Section 8.16 of [ISOBMFF].
The Media Initialization Section for an fMP4 Segment is an ISO Base
Media File that can initialize a parser for that Segment.
Broadly speaking, fMP4 Segments and Media Initialization Sections are
[ISOBMFF] files that also satisfy the constraints described in this
section.
The Media Initialization Section for an fMP4 Segment MUST contain a
File Type Box ('ftyp') containing a brand that is compatible with
'iso6' or higher. The File Type Box MUST be followed by a Movie Box.
The Movie Box MUST contain a Track Box ('trak') for every Track
Fragment Box ('traf') in the fMP4 Segment, with matching track_ID.
Each Track Box SHOULD contain a sample table, but its sample count
MUST be zero. Movie Header Boxes ('mvhd') and Track Header Boxes
('tkhd') MUST have durations of zero. The Movie Box MUST contain a
Movie Extends Box ('mvex'); it SHOULD follow the last Track Box.
Note that a Common Media Application Format [CMAF] Header meets all
these requirements.
In an fMP4 Segment, every Track Fragment Box MUST contain a Track
Fragment Decode Time Box ('tfdt'). fMP4 Segments MUST use movie-
fragment-relative addressing. fMP4 Segments MUST NOT use external
data references. Note that a CMAF Segment meets these requirements.
An fMP4 Segment in a Playlist containing the EXT-X-I-FRAMES-ONLY tag
(Section 4.4.3.6) MAY omit the portion of the Media Data Box
following the intra-coded frame (I-frame) sample data.
This specification makes no additional restrictions on [ISOBMFF]
boxes or box order. However, fMP4 Segments that indicate
compatibility with an additional standard, such as [CMAF], SHOULD
comply with whatever rules that standard requires.
Each fMP4 Segment in a Media Playlist MUST have an EXT-X-MAP tag
applied to it.
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3.1.3. Packed Audio
A Packed Audio Segment contains encoded audio samples and ID3 tags
that are simply packed together with minimal framing and no per-
sample timestamps. Supported Packed Audio formats are Advanced Audio
Coding (AAC) with Audio Data Transport Stream (ADTS) framing
[ISO_13818_7], MP3 [ISO_13818_3], AC-3 [AC_3], and Enhanced AC-3
[AC_3].
A Packed Audio Segment has no Media Initialization Section.
Each Packed Audio Segment MUST signal the timestamp of its first
sample with an ID3 Private frame (PRIV) tag [ID3] at the beginning of
the segment. The ID3 PRIV owner identifier MUST be
"com.apple.streaming.transportStreamTimestamp". The ID3 payload MUST
be a 33-bit MPEG-2 Program Elementary Stream timestamp expressed as a
big-endian eight-octet number, with the upper 31 bits set to zero.
Clients SHOULD NOT play Packed Audio Segments without this ID3 tag.
3.1.4. WebVTT
A WebVTT Segment is a section of a WebVTT [WebVTT] file. WebVTT
Segments carry subtitles.
The Media Initialization Section of a WebVTT Segment is the WebVTT
header.
Each WebVTT Segment MUST contain all subtitle cues that are intended
to be displayed during the period indicated by the segment EXTINF
duration. The start time offset and end time offset of each cue MUST
(with the single exception noted below) indicate the total display
time for that cue, even if part of the cue time range is outside the
Segment period. A WebVTT Segment MAY contain no cues; this indicates
that no subtitles are to be displayed during that period.
Under certain conditions, like live streaming, where it is not
possible to know the cue duration at the time of the segment creation
and the subtitle cue interval is split over multiple Segments, the
cue time range in each Segment MAY be limited to the WebVTT time
range covered by the Segment.
Each WebVTT Segment MUST either start with a WebVTT header or have an
EXT-X-MAP tag applied to it.
In order to synchronize timestamps between audio/video and subtitles,
an X-TIMESTAMP-MAP metadata header SHOULD be added to each WebVTT
header. This header maps WebVTT cue timestamps to media timestamps
in other Renditions of the Variant Stream. Its format is:
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X-TIMESTAMP-MAP=LOCAL:<cue time>,MPEGTS:<media time>
e.g., X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
indicating the media time to which the cue time MUST be mapped. The
cue timestamp in the LOCAL attribute MAY fall outside the range of
time covered by the segment.
The MPEGTS media timestamp MUST use a 90KHz timescale, even when non-
WebVTT Media Segments use a different timescale.
If a WebVTT segment does not have the X-TIMESTAMP-MAP, the client
MUST assume that the WebVTT cue time of 0 maps to an media timestamp
of 0.
When synchronizing WebVTT with PES timestamps, clients SHOULD account
for cases where the 33-bit PES timestamps have wrapped and the WebVTT
cue times have not. When the PES timestamp wraps, the WebVTT segment
SHOULD have a X-TIMESTAMP-MAP header that maps the current WebVTT
time to the new (low valued) PES timestamp.
3.1.5. IMSC Subtitles
An IMSC Segment is a Fragmented MPEG-4 (Section 3.1.2) Media Segment
that carries subtitle media according to MPEG-4 Part 30
[MP4_TIMED_TEXT]. This subtitle media MUST comply with the Text
Profile of IMSC1 [IMSC1].
The Media Initialization Section of an IMSC Segment is specified in
Section 3.1.2.
Each IMSC Segment MUST contain all subtitle samples that are intended
to be displayed during the period indicated by the segment EXTINF
duration. Each Segment MUST contain definitions for all styles which
are applied to any part of any sample in the Segment.
3.2. Partial Segments
One component of viewer delay in a live stream is publishing latency:
a Segment cannot be distributed until it has been completely encoded
and packaged. A long Segment encoded in real-time introduces a delay
equal to its duration. Partial Segments provide a parallel channel
for distributing media at the live edge of the Media Playlist, where
the media is divided into a larger number of smaller pieces, such as
CMAF Chunks. These subsets are called Partial Segments. Because
each Partial Segment has a short duration, it can be packaged,
published, and added to the Media Playlist much earlier than its
Parent Segment.
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A Partial Segment MUST be in one of the Supported Media Segment
Formats described in Section 3.1. A Partial Segment is associated
with a regular Media Segment, called its Parent Segment, by appearing
before it in the Media Playlist, and after the previous Media
Segment. Partial Segments are identified by the EXT-X-PART tag
(Section 4.4.4.9).
A Partial Segment MUST contain a subset of the media samples in its
Parent Segment. A Parent Segment and its entire set of Partial
Segments MUST contain the same set of media samples, with the same
timing and metadata.
Each Partial Segment has a Part Index, which is an integer indicating
the position of the Partial Segment within its Parent Segment. The
first Partial Segment has a Part Index of zero.
Each Partial Segment also has a Media Sequence Number, which is equal
to the Media Sequence Number of its Parent Segment.
4. Playlists
This section describes the Playlist files used by HTTP Live
Streaming. In this section, "MUST" and "MUST NOT" specify the rules
for the syntax and structure of legal Playlist files. Playlists that
violate these rules are invalid; clients MUST fail to parse them.
See Section 6.3.2.
The format of the Playlist files is derived from the M3U [M3U]
playlist file format and inherits two tags from that earlier file
format: EXTM3U (Section 4.4.1.1) and EXTINF (Section 4.4.4.1).
In the specification of tag syntax, a string enclosed by <>
identifies a tag parameter; its specific format is described in its
tag definition. If a parameter is further surrounded by [], it is
optional; otherwise, it is required.
Each Playlist file MUST be identifiable either by the path component
of its URI or by HTTP Content-Type. In the first case, the path MUST
end with either .m3u8 or .m3u. In the second, the HTTP Content-Type
MUST be "application/vnd.apple.mpegurl" or "audio/mpegurl". Clients
SHOULD refuse to parse Playlists that are not so identified.
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4.1. Definition of a Playlist
Playlist files MUST be encoded in UTF-8 [RFC3629]. They MUST NOT
contain any Byte Order Mark (BOM); clients SHOULD fail to parse
Playlists that contain a BOM or do not parse as UTF-8. Playlist
files MUST NOT contain UTF-8 control characters (U+0000 to U+001F and
U+007F to U+009F), with the exceptions of CR (U+000D) and LF
(U+000A). All character sequences MUST be normalized according to
Unicode normalization form "NFC" [UNICODE]. Note that US-ASCII
[US_ASCII] conforms to these rules.
Lines in a Playlist file are terminated by either a single line feed
character or a carriage return character followed by a line feed
character. Each line is a URI, is blank, or starts with the
character '#'. Blank lines are ignored. Whitespace MUST NOT be
present, except for elements in which it is explicitly specified.
Lines that start with the character '#' are either comments or tags.
Tags begin with #EXT. They are case sensitive. All other lines that
begin with '#' are comments and SHOULD be ignored.
A URI line identifies a Media Segment or a Playlist file (see
Section 4.4.6.2). Each Media Segment is specified by a URI and the
tags that apply to it.
A Playlist is a Media Playlist if all URI lines in the Playlist
identify Media Segments. A Playlist is a Multivariant Playlist if
all URI lines in the Playlist identify Media Playlists. A Playlist
MUST be either a Media Playlist or a Multivariant Playlist; all other
Playlists are invalid.
A URI in a Playlist, whether it is a URI line or part of a tag, MAY
be relative. Any relative URI is considered to be relative to the
URI of the Playlist that contains it.
The duration of a Media Playlist is the sum of the durations of the
Media Segments within it.
The segment bit rate of a Media Segment is the size of the Media
Segment divided by its EXTINF duration (Section 4.4.4.1). Note that
this includes container overhead but does not include overhead
imposed by the delivery system, such as HTTP, TCP, or IP headers.
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The peak segment bit rate of a Media Playlist is the largest bit rate
of any contiguous set of segments whose total duration is between 0.5
times the Target Duration and 1.5 times the Target Duration plus 0.5
seconds (since media segments may exceed the Target Duration by up to
0.5 seconds). The bit rate of a set is calculated by dividing the
sum of the segment sizes by the sum of the segment durations.
The average segment bit rate of a Media Playlist is the sum of the
sizes (in bits) of every Media Segment in the Media Playlist, divided
by the Media Playlist duration. Note that this includes container
overhead, but not HTTP or other overhead imposed by the delivery
system.
4.2. Attribute Lists
Certain tags have values that are attribute-lists. An attribute-list
is a comma-separated list of attribute/value pairs with no
whitespace.
An attribute/value pair has the following syntax:
AttributeName=AttributeValue
An AttributeName is an unquoted string containing characters from the
set [A..Z], [0..9], and '-'. Therefore, AttributeNames contain only
uppercase letters, not lowercase. There MUST NOT be any whitespace
between the AttributeName and the '=' character, nor between the '='
character and the AttributeValue.
An AttributeValue is one of the following:
* decimal-integer: an unquoted string of characters from the set
[0..9] expressing an integer in base-10 arithmetic in the range
from 0 to 2^64-1 (18446744073709551615). A decimal-integer may be
from 1 to 20 characters long.
* hexadecimal-sequence: an unquoted string of characters from the
set [0..9] and [A..F] that is prefixed with 0x or 0X. The maximum
length of a hexadecimal-sequence depends on its AttributeNames.
* decimal-floating-point: an unquoted string of characters from the
set [0..9] and '.' that expresses a non-negative floating-point
number in decimal positional notation.
* signed-decimal-floating-point: an unquoted string of characters
from the set [0..9], '-', and '.' that expresses a signed
floating-point number in decimal positional notation.
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* quoted-string: a string of characters within a pair of double
quotes (0x22). The following characters MUST NOT appear in a
quoted-string: line feed (0xA), carriage return (0xD), or double
quote (0x22). The string MUST be non-empty, unless specifically
allowed. Quoted-string AttributeValues SHOULD be constructed so
that byte-wise comparison is sufficient to test two quoted-string
AttributeValues for equality. Note that this implies case-
sensitive comparison.
* enumerated-string: an unquoted character string from a set that is
explicitly defined by the AttributeName. An enumerated-string
will never contain double quotes ("), commas (,), or whitespace.
* enumerated-string-list: a quoted-string containing a comma-
separated list of enumerated-strings from a set that is explicitly
defined by the AttributeName. Each enumerated-string in the list
is a string consisting of characters valid in an enumerated-
string. The list SHOULD NOT repeat any enumerated-string. To
support forward compatibility, clients MUST ignore any
unrecognized enumerated-strings in an enumerated-string-list.
* decimal-resolution: two decimal-integers separated by the "x"
character. The first integer is a horizontal pixel dimension
(width); the second is a vertical pixel dimension (height).
The type of the AttributeValue for a given AttributeName is specified
by the attribute definition.
A given AttributeName MUST NOT appear more than once in a given
attribute-list. Clients SHOULD refuse to parse such Playlists.
4.3. Variable Substitution
The following Playlist elements are subject to variable substitution:
* URI lines
* quoted-string AttributeValues
* hexadecimal-sequence AttributeValues
A Variable Reference is a string of the form "{$" (0x7B,0x24)
followed by a Variable Name followed by "}" (0x7D). Variable Names
are defined by the EXT-X-DEFINE tag (Section 4.4.2.3).
See Section 6.3.1 for more information about variable substitution.
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4.4. Playlist Tags
Playlist tags specify either global parameters of the Playlist or
information about the Media Segments or Media Playlists that appear
after them.
4.4.1. Basic Tags
These tags are allowed in both Media Playlists and Multivariant
Playlists.
4.4.1.1. EXTM3U
The EXTM3U tag indicates that the file is an Extended M3U [M3U]
Playlist file. It MUST be the first line of every Media Playlist and
every Multivariant Playlist. Its format is:
#EXTM3U
4.4.1.2. EXT-X-VERSION
The EXT-X-VERSION tag indicates the compatibility version of the
Playlist file, its associated media, and its server.
The EXT-X-VERSION tag applies to the entire Playlist file. Its
format is:
#EXT-X-VERSION:<n>
where n is an integer indicating the protocol compatibility version
number.
It MUST appear in all Playlists containing tags or attributes that
are not compatible with protocol version 1 to support
interoperability with older clients. Section 8 specifies the minimum
value of the compatibility version number for any given Playlist
file.
A Playlist file MUST NOT contain more than one EXT-X-VERSION tag. If
a client encounters a Playlist with multiple EXT-X-VERSION tags, it
MUST fail to parse it.
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4.4.2. Media or Multivariant Playlist Tags
The tags in this section can appear in either Multivariant Playlists
or Media Playlists. If one of these tags appears in a Multivariant
Playlist, it SHOULD NOT appear in any Media Playlist referenced by
that Multivariant Playlist. A tag that appears in both MUST have the
same value; otherwise, clients SHOULD ignore the value in the Media
Playlist(s).
Tags in this section MUST NOT appear more than once in a Playlist.
If one does, clients MUST fail to parse the Playlist. The only
exception to this rule is EXT-X-DEFINE, which MAY appear more than
once.
4.4.2.1. EXT-X-INDEPENDENT-SEGMENTS
The EXT-X-INDEPENDENT-SEGMENTS tag indicates that all media samples
in a Media Segment can be decoded without information from other
segments. It applies to every Media Segment in the Playlist.
Its format is:
#EXT-X-INDEPENDENT-SEGMENTS
If the EXT-X-INDEPENDENT-SEGMENTS tag appears in a Multivariant
Playlist, it applies to every Media Segment in every Media Playlist
in the Multivariant Playlist.
4.4.2.2. EXT-X-START
The EXT-X-START tag indicates a preferred point at which to start
playing a Playlist. By default, clients SHOULD start playback at
this point when beginning a playback session. This tag is OPTIONAL.
Its format is:
#EXT-X-START:<attribute-list>
The following attributes are defined:
TIME-OFFSET
The value of TIME-OFFSET is a signed-decimal-floating-point number
of seconds. A positive number indicates a time offset from the
beginning of the Playlist. A negative number indicates a negative
time offset from the end of the last Media Segment in the
Playlist. This attribute is REQUIRED.
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The absolute value of TIME-OFFSET SHOULD NOT be larger than the
Playlist duration. If the absolute value of TIME-OFFSET exceeds
the duration of the Playlist, it indicates either the end of the
Playlist (if positive) or the beginning of the Playlist (if
negative).
If the Playlist does not contain the EXT-X-ENDLIST tag, the TIME-
OFFSET SHOULD NOT be within three Target Durations of the end of
the Playlist file.
PRECISE
The value is an enumerated-string; valid strings are YES and NO.
If the value is YES, clients SHOULD start playback at the Media
Segment containing the TIME-OFFSET, but SHOULD NOT render media
samples in that segment whose presentation times are prior to the
TIME-OFFSET. If the value is NO, clients SHOULD attempt to render
every media sample in that segment. This attribute is OPTIONAL.
If it is missing, its value should be treated as NO.
4.4.2.3. EXT-X-DEFINE
The EXT-X-DEFINE tag provides a Playlist variable definition or
declaration. This tag is OPTIONAL.
Its format is:
#EXT-X-DEFINE:<attribute-list>
The following attributes are defined:
NAME
The value is a quoted-string which specifies the Variable Name.
All characters in the quoted-string MUST be from the following
set: [a..z], [A..Z], [0..9], '-', and '_'.
VALUE
The value is a quoted-string which specifies the Variable Value.
This attribute is REQUIRED if the EXT-X-DEFINE tag has a NAME
attribute. The quoted-string MAY be empty.
IMPORT
The value is a quoted-string which specifies the Variable Name and
indicates that its value is that of the variable of the same name
in the Multivariant Playlist. The valid character set is the same
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as for the NAME attribute. EXT-X-DEFINE tags containing the
IMPORT attribute MUST NOT occur in Multivariant Playlists; they
are only allowed in Media Playlists.
If the IMPORT attribute value does not match any Variable Name
declared in the Multivariant Playlist, or if the Media Playlist
was not loaded from a Multivariant Playlist, the parser MUST fail
to parse the Playlist.
An EXT-X-DEFINE tag MUST contain either a NAME or an IMPORT
attribute, but not both.
An EXT-X-DEFINE tag MUST NOT specify the same Variable Name as any
other EXT-X-DEFINE tag in the same Playlist. Parsers that encounter
duplicate Variable Name declarations MUST fail to parse the Playlist.
Variable Names are case-sensitive.
EXT-X-DEFINE tags do NOT implicitly persist across Playlist reloads.
4.4.3. Media Playlist Tags
Media Playlist tags describe global parameters of the Media Playlist.
There MUST NOT be more than one Media Playlist tag of each type in
any Media Playlist.
A Media Playlist tag MUST NOT appear in a Multivariant Playlist
4.4.3.1. EXT-X-TARGETDURATION
The EXT-X-TARGETDURATION tag specifies the Target Duration, an upper
bound on the duration of all Media Segments in the Playlist. The
EXTINF duration of each Media Segment in a Playlist file, when
rounded to the nearest integer, MUST be less than or equal to the
Target Duration. Longer segments can trigger playback stalls or
other errors. It applies to the entire Playlist file. Its format
is:
#EXT-X-TARGETDURATION:<s>
where s is a decimal-integer indicating the Target Duration in
seconds. The EXT-X-TARGETDURATION tag is REQUIRED.
4.4.3.2. EXT-X-MEDIA-SEQUENCE
The EXT-X-MEDIA-SEQUENCE tag indicates the Media Sequence Number of
the first Media Segment that appears in a Playlist file. Its format
is:
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#EXT-X-MEDIA-SEQUENCE:<number>
where number is a decimal-integer.
If the Media Playlist file does not contain an EXT-X-MEDIA-SEQUENCE
tag, then the Media Sequence Number of the first Media Segment in the
Media Playlist SHALL be considered to be 0. A client MUST NOT assume
that segments with the same Media Sequence Number in different Media
Playlists contain matching content (see Section 6.3.2).
A URI for a Media Segment is not required to contain its Media
Sequence Number.
See Section 6.2.1 and Section 6.3.5 for more information on setting
the EXT-X-MEDIA-SEQUENCE tag.
The EXT-X-MEDIA-SEQUENCE tag MUST appear before the first Media
Segment in the Playlist.
4.4.3.3. EXT-X-DISCONTINUITY-SEQUENCE
The EXT-X-DISCONTINUITY-SEQUENCE tag allows synchronization between
different Renditions of the same Variant Stream or different Variant
Streams that have EXT-X-DISCONTINUITY tags in their Media Playlists.
Its format is:
#EXT-X-DISCONTINUITY-SEQUENCE:<number>
where number is a decimal-integer.
If the Media Playlist does not contain an EXT-X-DISCONTINUITY-
SEQUENCE tag, then the Discontinuity Sequence Number of the first
Media Segment in the Playlist SHALL be considered to be 0.
The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before the first
Media Segment in the Playlist.
The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before any EXT-
X-DISCONTINUITY tag.
See Section 6.2.1 and Section 6.2.2 for more information about
setting the value of the EXT-X-DISCONTINUITY-SEQUENCE tag.
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4.4.3.4. EXT-X-ENDLIST
The EXT-X-ENDLIST tag indicates that no more Media Segments will be
added to the Media Playlist file. It MAY occur anywhere in the Media
Playlist file. Its format is:
#EXT-X-ENDLIST
4.4.3.5. EXT-X-PLAYLIST-TYPE
The EXT-X-PLAYLIST-TYPE tag provides mutability information about the
Media Playlist file. It applies to the entire Media Playlist file.
It is OPTIONAL. Its format is:
#EXT-X-PLAYLIST-TYPE:<type-enum>
where type-enum is either EVENT or VOD.
Section 6.2.1 defines the implications of the EXT-X-PLAYLIST-TYPE
tag.
If the EXT-X-PLAYLIST-TYPE value is EVENT, Media Segments can only be
added to the end of the Media Playlist. If the EXT-X-PLAYLIST-TYPE
value is Video On Demand (VOD), the Media Playlist cannot change.
If the EXT-X-PLAYLIST-TYPE tag is omitted from a Media Playlist, the
Playlist can be updated according to the rules in Section 6.2.1 with
no additional restrictions. For example, a live Playlist
(Section 6.2.2) MAY be updated to remove Media Segments in the order
that they appeared.
4.4.3.6. EXT-X-I-FRAMES-ONLY
The EXT-X-I-FRAMES-ONLY tag indicates that each Media Segment in the
Playlist describes a single I-frame. I-frames are encoded video
frames whose decoding does not depend on any other frame. I-frame
Playlists can be used for trick play, such as fast forward, rapid
reverse, and scrubbing.
The EXT-X-I-FRAMES-ONLY tag applies to the entire Playlist. Its
format is:
#EXT-X-I-FRAMES-ONLY
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In a Playlist with the EXT-X-I-FRAMES-ONLY tag, the Media Segment
duration (EXTINF tag value) is the time between the presentation time
of the I-frame in the Media Segment and the presentation time of the
next I-frame in the Playlist, or the end of the presentation if it is
the last I-frame in the Playlist.
Media resources containing I-frame segments MUST begin with either a
Media Initialization Section (Section 3) or be accompanied by an EXT-
X-MAP tag indicating the Media Initialization Section so that clients
can load and decode I-frame segments in any order. The byte range of
an I-frame segment with an EXT-X-BYTERANGE tag applied to it
(Section 4.4.4.2) MUST NOT include its Media Initialization Section;
clients can assume that the Media Initialization Section is defined
by the EXT-X-MAP tag, or is located between the start of the resource
and the offset of the first I-frame segment in that resource.
Use of the EXT-X-I-FRAMES-ONLY REQUIRES a compatibility version
number of 4 or greater.
4.4.3.7. EXT-X-PART-INF
The EXT-X-PART-INF tag provides information about the Partial
Segments in the Playlist. It is REQUIRED if a Playlist contains one
or more EXT-X-PART tags. Its format is:
#EXT-X-PART-INF:<attribute-list>
The following attributes are defined:
PART-TARGET
The value is a decimal-floating-point number of seconds indicating
the Part Target Duration. This attribute is REQUIRED.
4.4.3.8. EXT-X-SERVER-CONTROL
The EXT-X-SERVER-CONTROL tag allows the Server to indicate support
for Delivery Directives (Section 6.2.5). Its format is:.
#EXT-X-SERVER-CONTROL:<attribute-list>
The following attributes are defined:
CAN-SKIP-UNTIL
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Indicates that the Server can produce Playlist Delta Updates
(Section 6.2.5.1) in response to the _HLS_skip Delivery Directive.
Its value is the Skip Boundary, a decimal-floating-point number of
seconds. The Skip Boundary MUST be at least six times the Target
Duration.
This attribute is OPTIONAL. It MAY appear in any Media Playlist.
CAN-SKIP-DATERANGES
The value is an enumerated-string whose value is YES if the Server
can produce Playlist Delta Updates (Section 6.2.5.1) that skip
older EXT-X-DATERANGE tags in addition to Media Segments.
This attribute is OPTIONAL. It REQUIRES the presence of the CAN-
SKIP-UNTIL attribute.
HOLD-BACK
The value is a decimal-floating-point number of seconds that
indicates the server-recommended minimum distance from the end of
the Playlist at which clients should begin to play or to which
they should seek, unless PART-HOLD-BACK applies. Its value MUST
be at least three times the Target Duration.
This attribute is OPTIONAL. Its absence implies a value of three
times the Target Duration. It MAY appear in any Media Playlist.
PART-HOLD-BACK
The value is a decimal-floating-point number of seconds that
indicates the server-recommended minimum distance from the end of
the Playlist at which clients should begin to play or to which
they should seek when playing in Low-Latency Mode. Its value MUST
be at least twice the Part Target Duration. Its value SHOULD be
at least three times the Part Target Duration. If different
Renditions have different Part Target Durations then PART-HOLD-
BACK SHOULD be at least three times the maximum Part Target
Duration.
PART-HOLD-BACK is REQUIRED if the Playlist contains the EXT-X-
PART-INF tag.
CAN-BLOCK-RELOAD
The value is an enumerated-string whose value is YES if the server
supports Blocking Playlist Reload (Section 6.2.5.2). This
attribute is OPTIONAL; its absence implies no support.
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4.4.4. Media Segment Tags
Each Media Segment is specified by a series of Media Segment tags
followed by a URI. Some Media Segment tags apply to just the next
segment; others apply to all subsequent segments until another
instance of the same tag.
A Media Segment tag MUST NOT appear in a Multivariant Playlist.
Clients MUST fail to parse Playlists that contain both Media Segment
tags and Multivariant Playlist tags (Section 4.4.6).
4.4.4.1. EXTINF
The EXTINF tag specifies the duration of a Media Segment. It applies
only to the next Media Segment. This tag is REQUIRED for each Media
Segment. Its format is:
#EXTINF:<duration>,[<title>]
where duration is a decimal-floating-point or decimal-integer number
(as described in Section 4.2) that specifies the duration of the
Media Segment in seconds and title is the remainder of the line
following the comma. Durations SHOULD be decimal-floating-point,
with enough accuracy to avoid perceptible error when segment
durations are accumulated. However, if the compatibility version
number is less than 3, durations MUST be integers. Durations that
are reported as integers SHOULD be rounded to the nearest integer.
The title is an optional human-readable informative title of the
Media Segment expressed as UTF-8 text. If title is zero length or
entirely whitespace, the title is considered to be missing.
4.4.4.2. EXT-X-BYTERANGE
The EXT-X-BYTERANGE tag indicates that a Media Segment is a sub-range
of the resource identified by its URI. It applies only to the next
URI line that follows it in the Playlist. Its format is:
#EXT-X-BYTERANGE:<n>[@<o>]
where n is a decimal-integer indicating the length of the sub-range
in bytes. If present, o is a decimal-integer indicating the start of
the sub-range, as a byte offset from the beginning of the resource.
If o is not present, the sub-range begins at the next byte following
the sub-range of the previous Media Segment.
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If o is not present, a previous Media Segment MUST appear in the
Playlist file and MUST be a sub-range of the same media resource, or
the Media Segment is undefined and the client MUST fail to parse the
Playlist.
A Media Segment without an EXT-X-BYTERANGE tag consists of the entire
resource identified by its URI.
Use of the EXT-X-BYTERANGE tag REQUIRES a compatibility version
number of 4 or greater.
4.4.4.3. EXT-X-DISCONTINUITY
The EXT-X-DISCONTINUITY tag indicates a discontinuity between the
Media Segment that follows it and the one that preceded it.
Its format is:
#EXT-X-DISCONTINUITY
The EXT-X-DISCONTINUITY tag MUST be present if there is a change in
any of the following characteristics:
* file format
* number, type, and identifiers of tracks
* timestamp sequence
The EXT-X-DISCONTINUITY tag SHOULD be present if there is a change in
any of the following characteristics:
* encoding parameters
* encoding sequence
See Section 3, Section 6.2.1, and Section 6.3.3 for more information
about the EXT-X-DISCONTINUITY tag.
4.4.4.4. EXT-X-KEY
Media Segments MAY be encrypted. The EXT-X-KEY tag specifies how to
decrypt them. It applies to every Media Segment and to every Media
Initialization Section declared by an EXT-X-MAP tag that appears
between it and the next EXT-X-KEY tag in the Playlist file with the
same KEYFORMAT attribute or a METHOD of NONE (or the end of the
Playlist file). Any Media Segment or Media Initialization
Section that precedes the first EXT-X-KEY tag is unencrypted. Two or
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more EXT-X-KEY tags with different KEYFORMAT attributes MAY apply to
the same Media Segment if they ultimately produce the same decryption
key. The format is:
#EXT-X-KEY:<attribute-list>
The following attributes are defined:
METHOD
The value is an enumerated-string that specifies the encryption
method. This attribute is REQUIRED.
The methods defined are: NONE, AES-128, and SAMPLE-AES.
An encryption method of NONE means that Media Segments are not
encrypted. If the encryption method is NONE, other attributes
MUST NOT be present.
An encryption method of AES-128 signals that Media Segments are
completely encrypted using the Advanced Encryption Standard (AES)
[AES_128] with a 128-bit key, Cipher Block Chaining (CBC), and
Public-Key Cryptography Standards #7 (PKCS7) padding [RFC5652].
CBC is restarted on each segment boundary, using either the
Initialization Vector (IV) attribute value or the Media Sequence
Number as the IV; see Section 5.2.
An alternative to whole-segment encryption is Sample Encryption.
With Sample Encryption, only media sample data - such as audio
packets or video frames - is encrypted. The rest of the Media
Segment is unencrypted. Sample Encryption allows parts of the
Segment to be processed without (or before) decrypting the media
itself.
An encryption method of SAMPLE-AES means that the Media Segments
are Sample Encrypted using the Advanced Encryption Standard
[AES_128]. How these media streams are encrypted and encapsulated
in a segment depends on the media encoding and the media format of
the segment. fMP4 Media Segments are encrypted using the 'cbcs'
scheme of Common Encryption [COMMON_ENC]. Encryption of other
Media Segment formats containing H.264 [H_264], AAC [ISO_14496],
AC-3 [AC_3], and Enhanced AC-3 [AC_3] media streams is described
in the HTTP Live Streaming (HLS) Sample Encryption specification
[SampleEnc]. The IV attribute MAY be present; see Section 5.2.
URI
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The value is a quoted-string containing a URI that specifies how
to obtain the key. This attribute is REQUIRED unless the METHOD
is NONE.
IV
The value is a hexadecimal-sequence that specifies a 128-bit
unsigned integer Initialization Vector to be used with the key.
Use of the IV attribute REQUIRES a compatibility version number of
2 or greater. See Section 5.2 for when the IV attribute is used.
KEYFORMAT
The value is a quoted-string that specifies how the key is
represented in the resource identified by the URI; see Section 5
for more detail. This attribute is OPTIONAL; its absence
indicates an implicit value of "identity". Use of the KEYFORMAT
attribute REQUIRES a compatibility version number of 5 or greater.
KEYFORMATVERSIONS
The value is a quoted-string containing one or more positive
integers separated by the "/" character (for example, "1", "1/2",
or "1/2/5"). If more than one version of a particular KEYFORMAT
is defined, this attribute can be used to indicate which
version(s) this instance complies with. This attribute is
OPTIONAL; if it is not present, its value is considered to be "1".
Use of the KEYFORMATVERSIONS attribute REQUIRES a compatibility
version number of 5 or greater.
If the Media Playlist file does not contain an EXT-X-KEY tag, then
Media Segments are not encrypted.
See Section 5 for the format of the Key file, and Section 5.2,
Section 6.2.3, and Section 6.3.6 for additional information on Media
Segment encryption.
4.4.4.5. EXT-X-MAP
The EXT-X-MAP tag specifies how to obtain the Media Initialization
Section (Section 3) required to parse the applicable Media Segments.
It applies to every Media Segment that appears after it in the
Playlist until the next EXT-X-MAP tag or until the end of the
Playlist.
Its format is:
#EXT-X-MAP:<attribute-list>
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The following attributes are defined:
URI
The value is a quoted-string containing a URI that identifies a
resource that contains the Media Initialization Section. This
attribute is REQUIRED.
BYTERANGE
The value is a quoted-string specifying a byte range into the
resource identified by the URI attribute. This range SHOULD
contain only the Media Initialization Section. The format of the
byte range is similar to that described in Section 4.4.4.2;
however, offset is REQUIRED "<n>@<o>". This attribute is
OPTIONAL; if it is not present, the byte range is the entire
resource indicated by the URI.
An EXT-X-MAP tag SHOULD be supplied for Media Segments in Playlists
with the EXT-X-I-FRAMES-ONLY tag when the first Media Segment (i.e.,
I-frame) in the Playlist (or the first segment following an EXT-
X-DISCONTINUITY tag) does not immediately follow the Media
Initialization Section at the beginning of its resource.
Use of the EXT-X-MAP tag in a Media Playlist that contains the EXT-
X-I-FRAMES-ONLY tag REQUIRES a compatibility version number of 5 or
greater. Use of the EXT-X-MAP tag in a Media Playlist that DOES NOT
contain the EXT-X-I-FRAMES-ONLY tag REQUIRES a compatibility version
number of 6 or greater.
If the Media Initialization Section declared by an EXT-X-MAP tag is
encrypted with a METHOD of AES-128, the IV attribute of the EXT-X-KEY
tag that applies to the EXT-X-MAP is REQUIRED.
4.4.4.6. EXT-X-PROGRAM-DATE-TIME
The EXT-X-PROGRAM-DATE-TIME tag associates the first sample of a
Media Segment with an absolute date and/or time. It applies only to
the next Media Segment. Its format is:
#EXT-X-PROGRAM-DATE-TIME:<date-time-msec>
where date-time-msec is an ISO/IEC 8601:2004 [ISO_8601] date/time
representation, such as YYYY-MM-DDThh:mm:ss.SSSZ. It SHOULD indicate
a time zone and fractional parts of seconds, to at least millisecond
accuracy.
For example:
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#EXT-X-PROGRAM-DATE-TIME:2010-02-19T14:54:23.031+08:00
See Section 6.2.1 and Section 6.3.3 for more information on the EXT-
X-PROGRAM-DATE-TIME tag.
4.4.4.7. EXT-X-GAP
The EXT-X-GAP tag indicates that the segment URI to which it applies
does not contain media data and SHOULD NOT be loaded by clients. It
applies only to the next Media Segment.
Its format is:
#EXT-X-GAP
See Section 6.2.1 and Section 6.3.3 for more information on the EXT-
X-GAP tag.
4.4.4.8. EXT-X-BITRATE
The EXT-X-BITRATE tag identifies the approximate segment bit rate of
the Media Segment(s) to which it applies. It applies to every Media
Segment between it and the next EXT-X-BITRATE tag in the Playlist
file (or the end of the Playlist file) that does not have an EXT-
X-BYTERANGE tag applied to it. Its format is:
#EXT-X-BITRATE:<rate>
where rate is a decimal-integer of kilobits per second.
This tag is OPTIONAL. If it is present then its value MUST be no
less than 90% of the segment bit rate of each Media Segment to which
it is applied and no greater than 110% of the segment bit rate of
each Media Segment to which it is applied.
4.4.4.9. EXT-X-PART
The EXT-X-PART tag identifies a Partial Segment. It is OPTIONAL.
Its format is:
#EXT-X-PART:<attribute-list>
The following attributes are defined:
URI
The value is a quoted-string containing the URI for the Partial
Segment. This attribute is REQUIRED.
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DURATION
The value is the duration of the Partial Segment as a decimal-
floating-point number of seconds. This attribute is REQUIRED.
INDEPENDENT
The value is an enumerated-string whose value is YES if the
Partial Segment contains an independent frame. This attribute is
OPTIONAL; however every Partial Segment containing an independent
frame SHOULD carry it to increase the efficiency with which
clients can join and switch Renditions.
BYTERANGE
Indicates that the Partial Segment is a sub-range of the resource
specified by the URI attribute. The value is a quoted-string
whose contents have the same format as the EXT-X-BYTERANGE tag:
"<n>[@<o>]". If o is not present, the sub-range begins at the
next byte following the sub-range of the previous Partial Segment
belonging to the same Parent Segment.
GAP
The value is an enumerated-string whose value is YES if the
Partial Segment is not available. It is REQUIRED for such Partial
Segments.
All Media Segment Tags (Section 4.4.4) except for EXT-X-BYTERANGE and
EXT-X-GAP that are applied to a Parent Segment MUST appear before the
first EXT-X-PART tag of that Parent Segment.
The duration of a Partial Segment MUST be less than or equal to the
Part Target Duration. The duration of each Partial Segment MUST be
at least 85% of the Part Target Duration, with the exception of
Partial Segments with the INDEPENDENT=YES or GAP=YES attribute,
Partial Segments that are immediately followed by a Partial Segment
with a GAP=YES attribute, and the final Partial Segment of any Parent
Segment.
4.4.5. Media Metadata Tags
Media Metadata tags provide information about the playlist that is
not associated with specific Media Segments. There MAY be more than
one Media Metadata tag of each type in any Media Playlist. The only
exception to this rule is EXT-X-SKIP, which MUST NOT appear more than
once.
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4.4.5.1. EXT-X-DATERANGE
The EXT-X-DATERANGE tag associates a Date Range (i.e., a range of
time defined by a starting and ending date) with a set of attribute/
value pairs. Its format is:
#EXT-X-DATERANGE:<attribute-list>
where the defined attributes are:
ID
A quoted-string that uniquely identifies a Date Range in the
Playlist. This attribute is REQUIRED.
CLASS
A client-defined quoted-string that specifies some set of
attributes and their associated value semantics. All Date Ranges
with the same CLASS attribute value MUST adhere to these
semantics. This attribute is OPTIONAL.
START-DATE
A quoted-string containing the [ISO_8601] date/time at which the
Date Range begins. This attribute is REQUIRED.
CUE
An enumerated-string-list of Trigger Identifiers. The list
collectively indicates when to trigger an action associated with
the Date Range. The time to trigger the action MAY be at a point
of playback outside the Date Range expressed by the START-DATE and
duration. The defined Trigger Identifiers are: PRE, POST, and
ONCE. This attribute is OPTIONAL.
END-DATE
A quoted-string containing the [ISO_8601] date/time at which the
Date Range ends. It MUST be equal to or later than the value of
the START-DATE attribute. This attribute is OPTIONAL.
DURATION
The duration of the Date Range expressed as a decimal-floating-
point number of seconds. It MUST NOT be negative. A single
instant in time (e.g., crossing a finish line) SHOULD be
represented with a duration of 0. This attribute is OPTIONAL.
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PLANNED-DURATION
The expected duration of the Date Range expressed as a decimal-
floating-point number of seconds. It MUST NOT be negative. This
attribute SHOULD be used to indicate the expected duration of a
Date Range whose actual duration is not yet known. It is
OPTIONAL.
X-<client-attribute>
The "X-" prefix defines a namespace reserved for client-defined
attributes. The client-attribute MUST be a legal AttributeName.
Clients SHOULD use a reverse-DNS syntax when defining their own
attribute names to avoid collisions. The attribute value MUST be
a quoted-string, a hexadecimal-sequence, or a decimal-floating-
point. An example of a client-defined attribute is X-COM-EXAMPLE-
AD-ID="XYZ123". These attributes are OPTIONAL.
SCTE35-CMD, SCTE35-OUT, SCTE35-IN
Used to carry SCTE-35 data; see Section 4.4.5.1.1 for more
information. These attributes are OPTIONAL.
END-ON-NEXT
An enumerated-string whose value MUST be YES. This attribute
indicates that the end of the range containing it is equal to the
START-DATE of its Following Range. The Following Range is the
Date Range of the same CLASS that has the earliest START-DATE
after the START-DATE of the range in question. This attribute is
OPTIONAL.
A CUE attribute containing PRE indicates that an action is to be
triggered before playback of the primary asset begins, regardless of
where playback begins in the primary asset.
A CUE attribute containing POST indicates that an action is to be
triggered after the primary asset has been played to its end without
error.
The presence of a CUE attribute that contains ONCE indicates that an
action is to be triggered once. It SHOULD NOT be triggered again,
even if the user replays the portion of the primary asset that
includes the trigger point.
A CUE attribute MUST NOT include both PRE and POST.
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An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST have a
CLASS attribute. Other EXT-X-DATERANGE tags with the same CLASS
attribute MUST NOT specify Date Ranges that overlap.
An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST NOT
contain DURATION or END-DATE attributes.
A Date Range with neither a DURATION, an END-DATE, nor an END-ON-
NEXT=YES attribute has an unknown duration, even if it has a PLANNED-
DURATION.
If a Playlist contains an EXT-X-DATERANGE tag, it MUST also contain
at least one EXT-X-PROGRAM-DATE-TIME tag.
If a Playlist contains two EXT-X-DATERANGE tags with the same ID
attribute value, then any AttributeName that appears in both tags
MUST have the same AttributeValue.
If a Date Range contains both a DURATION attribute and an END-DATE
attribute, the value of the END-DATE attribute MUST be equal to the
value of the START-DATE attribute plus the value of the DURATION
attribute.
Clients SHOULD ignore EXT-X-DATERANGE tags with illegal syntax.
4.4.5.1.1. Mapping SCTE-35 into EXT-X-DATERANGE
Splice information carried in source media according to the SCTE-35
specification [SCTE35] MAY be represented in a Media Playlist using
EXT-X-DATERANGE tags.
Each SCTE-35 splice_info_section() containing a splice_null(),
splice_schedule(), bandwidth_reservation(), or private_cmd() SHOULD
be represented by an EXT-X-DATERANGE tag with an SCTE35-CMD attribute
whose value is the big-endian binary representation of the
splice_info_section(), expressed as a hexadecimal-sequence.
An SCTE-35 splice out/in pair signaled by a pair of splice_insert()
commands SHOULD be represented by one or more EXT-X-DATERANGE tags
carrying the same ID attribute, which MUST be unique to that splice
out/in pair. The "out" splice_info_section() (with
out_of_network_indicator set to 1) MUST be placed in an SCTE35-OUT
attribute, with the same formatting as SCTE35-CMD. The "in"
splice_info_section() (with out_of_network_indicator set to 0) MUST
be placed in an SCTE35-IN attribute, with the same formatting as
SCTE35-CMD.
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An SCTE-35 splice out/in pair signaled by a pair of time_signal()
commands, each carrying a single segmentation_descriptor(), SHOULD be
represented by one or more EXT-X-DATERANGE tags carrying the same ID
attribute, which MUST be unique to that splice out/in pair. The
"out" splice_info_section() MUST be placed in an SCTE35-OUT
attribute; the "in" splice_info_section() MUST be placed in an
SCTE35-IN attribute.
Different types of segmentation, as indicated by the
segmentation_type_id in the segmentation_descriptor(), SHOULD be
represented by separate EXT-X-DATERANGE tags, even if two or more
segmentation_descriptor()s arrive in the same splice_info_section().
In that case, each EXT-X-DATERANGE tag will have an SCTE35-OUT,
SCTE35-IN, or SCTE35-CMD attribute whose value is the entire
splice_info_section().
An SCTE-35 time_signal() command that does not signal a splice out or
in point SHOULD be represented by an EXT-X-DATERANGE tag with an
SCTE35-CMD attribute.
The START-DATE of an EXT-X-DATERANGE tag containing an SCTE35-OUT
attribute MUST be the date and time that corresponds to the program
time of that splice.
The START-DATE of an EXT-X-DATERANGE tag containing an SCTE35-CMD
MUST be the date and time specified by the splice_time() in the
command or the program time at which the command appeared in the
source stream if the command does not specify a splice_time().
An EXT-X-DATERANGE tag containing an SCTE35-OUT attribute MAY contain
a PLANNED-DURATION attribute. Its value MUST be the planned duration
of the splice.
The DURATION of an EXT-X-DATERANGE tag containing an SCTE35-IN
attribute MUST be the actual (not planned) program duration between
the corresponding out-point and that in-point.
The END-DATE of an EXT-X-DATERANGE tag containing an SCTE35-IN
attribute MUST be the actual (not planned) program date and time of
that in-point.
If the actual end date and time is not known when an SCTE35-OUT
attribute is added to the Playlist, the DURATION attribute and the
END-TIME attribute MUST NOT be present; the actual end date of the
splice SHOULD be signaled by another EXT-X-DATERANGE tag once it has
been established.
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A canceled splice SHOULD NOT appear in the Playlist as an EXT-
X-DATERANGE tag.
An EXT-X-DATERANGE tag announcing a splice SHOULD be added to a
Playlist at the same time as the last pre-splice Media Segment, or
earlier if possible.
The ID attribute of an EXT-X-DATERANGE tag MAY contain a
splice_event_id and/or a segmentation_event_id, but it MUST be unique
in the Playlist. If there is a possibility that an SCTE-35 id will
be reused, the ID attribute value MUST include disambiguation, such
as a date or sequence number.
4.4.5.2. EXT-X-SKIP
A server produces a Playlist Delta Update (Section 6.2.5.1), by
replacing tags earlier than the Skip Boundary with an EXT-X-SKIP tag.
When replacing Media Segments, the EXT-X-SKIP tag replaces the
segment URI lines and all Media Segment Tags tags that are applied to
those segments. This tag MUST NOT appear more than once in a
Playlist
Its format is:
#EXT-X-SKIP:<attribute-list>
The following attributes are defined:
SKIPPED-SEGMENTS
The value is a decimal-integer specifying the number of Media
Segments replaced by the EXT-X-SKIP tag. This attribute is
REQUIRED.
RECENTLY-REMOVED-DATERANGES
The value is a quoted-string consisting of a tab (0x9) delimited
list of EXT-X-DATERANGE IDs that have been removed from the
Playlist recently. See Section 6.2.5.1 for more information.
This attribute is REQUIRED if the Client requested an update that
skips EXT-X-DATERANGE tags. The quoted-string MAY be empty.
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4.4.5.3. EXT-X-PRELOAD-HINT
The EXT-X-PRELOAD-HINT tag allows a Client loading media from a live
stream to reduce the time to obtain a resource from the Server by
issuing its request before the resource is available to be delivered.
The server will hold onto the request ("block") until it can respond.
Its format is:
#EXT-X-PRELOAD-HINT:<attribute-list>
The following attributes are defined:
TYPE
The value is an enumerated-string that specifies the type of the
hinted resource. If the value is PART, the resource is a Partial
Segment. If the value is MAP, the resource is a Media
Initialization Section. This attribute is REQUIRED.
URI
The value is a quoted-string containing a URI identifying the
hinted resource. It MUST match the URI that will be subsequently
added to the Playlist as a non-hinted resource (for example, the
URI of an EXT-X-PART tag). The URI MAY be relative to the URI of
the Playlist or it MAY be absolute. The hostname MAY differ from
the hostname of the Playlist URI. This attribute is REQUIRED.
BYTERANGE-START
The value is a decimal-integer specifying the byte offset of the
first byte of the hinted resource, from the beginning of the
resource identified by the URI attribute. This attribute is
OPTIONAL. Its absence implies a value of 0.
BYTERANGE-LENGTH
The value is a decimal-integer specifying the length of the hinted
resource. This attribute is OPTIONAL. Its absence indicates that
the last byte of the hinted resource is the last byte of the
resource identified by the URI attribute. In this case, you
SHOULD use the recommended last-byte-pos [RFC8673] value of
2^^53-1 (9007199254740991) in the HTTP Range request.
Note that when a hinted Partial Segment eventually appears in the
Playlist as an EXT-X-PART tag, it MAY have a different Discontinuity
Sequence Number, Media Initialization Section, or encryption
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configuration. In other words, the Partial Segment can be preceded
by an EXTINF tag indicating the end of the previous Parent Segment
and an EXT-X-DISCONTINUITY, EXT-X-MAP, or EXT-X-KEY tag.
A Playlist containing an EXT-X-ENDLIST tag MUST NOT contain an EXT-X-
PRELOAD-HINT tag.
4.4.5.4. EXT-X-RENDITION-REPORT
The EXT-X-RENDITION-REPORT tag carries information about an
associated Rendition that is as up-to-date as the Playlist that
contains it. Its format is:
#EXT-X-RENDITION-REPORT:<attribute-list>
The following attributes are defined:
URI
The value is a quoted-string containing the URI for the Media
Playlist of the specified Rendition. It MUST be relative to the
URI of the Media Playlist containing the EXT-X-RENDITION-REPORT
tag. This attribute is REQUIRED.
LAST-MSN
The value is a decimal-integer specifying the Media Sequence
Number of the last Media Segment currently in the specified
Rendition. If the Rendition contains Partial Segments then this
value is the Media Sequence Number of the last Partial Segment.
This attribute is REQUIRED.
LAST-PART
The value is a decimal-integer that indicates the Part Index of
the last Partial Segment currently in the specified Rendition
whose Media Sequence Number is equal to the LAST-MSN attribute
value. This attribute is REQUIRED if the Rendition contains a
Partial Segment.
A server MAY omit adding an attribute to an EXT-X-RENDITION-REPORT
tag - even a mandatory attribute - if its value is the same as that
of the Rendition Report of the Media Playlist to which the EXT-X-
RENDITION-REPORT tag is being added. Doing so reduces the size of
the Rendition Report.
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4.4.6. Multivariant Playlist Tags
Multivariant Playlist tags define the Variant Streams, Renditions,
and other global parameters of the presentation.
Multivariant Playlist tags MUST NOT appear in a Media Playlist;
clients MUST fail to parse any Playlist that contains both a
Multivariant Playlist tag and either a Media Playlist tag or a Media
Segment tag.
4.4.6.1. EXT-X-MEDIA
The EXT-X-MEDIA tag is used to relate Media Playlists that contain
alternative Renditions (Section 4.4.6.2.1) of the same content. For
example, three EXT-X-MEDIA tags can be used to identify audio-only
Media Playlists that contain English, French, and Spanish Renditions
of the same presentation. Or, two EXT-X-MEDIA tags can be used to
identify video-only Media Playlists that show two different camera
angles.
Its format is:
#EXT-X-MEDIA:<attribute-list>
The following attributes are defined:
TYPE
The value is an enumerated-string; valid strings are AUDIO, VIDEO,
SUBTITLES, and CLOSED-CAPTIONS. This attribute is REQUIRED.
Typically, closed-caption [CEA608] media is carried in the video
stream. Therefore, an EXT-X-MEDIA tag with TYPE of CLOSED-
CAPTIONS does not specify a Rendition; the closed-caption media is
present in the Media Segments of every video Rendition.
URI
The value is a quoted-string containing a URI that identifies the
Media Playlist file. This attribute is OPTIONAL; see
Section 4.4.6.2.1. If the TYPE is CLOSED-CAPTIONS, the URI
attribute MUST NOT be present.
GROUP-ID
The value is a quoted-string that specifies the group to which the
Rendition belongs. See Section 4.4.6.1.1. This attribute is
REQUIRED.
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LANGUAGE
The value is a quoted-string containing one of the standard Tags
for Identifying Languages [RFC5646], which identifies the primary
language used in the Rendition. This attribute is OPTIONAL.
ASSOC-LANGUAGE
The value is a quoted-string containing a language tag [RFC5646]
that identifies a language that is associated with the Rendition.
An associated language is often used in a different role than the
language specified by the LANGUAGE attribute (e.g., written versus
spoken, or a fallback dialect). This attribute is OPTIONAL.
NAME
The value is a quoted-string containing a human-readable
description of the Rendition. If the LANGUAGE attribute is
present, then this description SHOULD be in that language. This
attribute is REQUIRED.
STABLE-RENDITION-ID
The value is a quoted-string which is a stable identifier for the
URI within the Multivariant Playlist. All characters in the
quoted-string MUST be from the following set: [a..z], [A..Z],
[0..9], '+', '/', '=', '.', '-', and '_'. This attribute is
OPTIONAL.
The STABLE-RENDITION-ID allows the URI of a Rendition to change
between two distinct downloads of the Multivariant Playlist. IDs
are matched using a byte-for-byte comparison.
All EXT-X-MEDIA tags in a Multivariant Playlist with the same URI
value SHOULD use the same STABLE-RENDITION-ID.
DEFAULT
The value is an enumerated-string; valid strings are YES and NO.
If the value is YES, then the client SHOULD play this Rendition of
the content in the absence of information from the user indicating
a different choice. This attribute is OPTIONAL. Its absence
indicates an implicit value of NO.
AUTOSELECT
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The value is an enumerated-string; valid strings are YES and NO.
This attribute is OPTIONAL. Its absence indicates an implicit
value of NO. If the value is YES, then the client MAY choose to
play this Rendition in the absence of explicit user preference
because it matches the current playback environment, such as
chosen system language.
If the AUTOSELECT attribute is present, its value MUST be YES if
the value of the DEFAULT attribute is YES.
FORCED
The value is an enumerated-string; valid strings are YES and NO.
This attribute is OPTIONAL. Its absence indicates an implicit
value of NO. The FORCED attribute MUST NOT be present unless the
TYPE is SUBTITLES.
A value of YES indicates that the Rendition contains content that
is considered essential to play. When selecting a FORCED
Rendition, a client SHOULD choose the one that best matches the
current playback environment (e.g., language).
A value of NO indicates that the Rendition contains content that
is intended to be played in response to explicit user request.
INSTREAM-ID
The value is a quoted-string that specifies a Rendition within the
segments in the Media Playlist. This attribute is REQUIRED if the
TYPE attribute is CLOSED-CAPTIONS, in which case it MUST have one
of the values: "CC1", "CC2", "CC3", "CC4", or "SERVICEn" where n
MUST be an integer between 1 and 63 (e.g., "SERVICE9" or
"SERVICE42").
The values "CC1", "CC2", "CC3", and "CC4" identify a Line 21 Data
Services channel [CEA608]. The "SERVICE" values identify a
Digital Television Closed Captioning [CEA708] service block
number.
For all other TYPE values, the INSTREAM-ID MUST NOT be specified.
CHARACTERISTICS
The value is a quoted-string containing one or more Media
Characteristic Tags (MCTs) separated by comma (,) characters. A
Media Characteristic Tag has the same format as the payload of a
media characteristic tag atom [MCT] This attribute is OPTIONAL.
Each MCT indicates an individual characteristic of the Rendition.
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A SUBTITLES Rendition MAY include the following characteristics:
"public.accessibility.transcribes-spoken-dialog",
"public.accessibility.describes-music-and-sound", and
"public.easy-to-read" (which indicates that the subtitles have
been edited for ease of reading).
An AUDIO Rendition MAY include the following characteristic:
"public.accessibility.describes-video".
The CHARACTERISTICS attribute MAY include private MCTs.
CHANNELS
The value is a quoted-string that specifies an ordered, slash-
separated ("/") list of parameters.
If the TYPE attribute is AUDIO, then the first parameter is a
count of audio channels expressed as a decimal-integer, indicating
the maximum number of independent, simultaneous audio channels
present in any Media Segment in the Rendition. For example, an
AC-3 5.1 Rendition would have a CHANNELS="6" attribute.
If the TYPE attribute is AUDIO, then the second parameter
identifies non-channel-based audio coding, such as object-based
audio, used by the Rendition. This parameter is a comma-separated
list of Audio Coding Identifiers. It is optional. An Audio
Coding Identifier is a string containing characters from the set
[A..Z], [0..9], and '-'. They are codec-specific. A parameter
value of consisting solely of the dash character (0x2D) indicates
that the audio is only channel-based.
No other CHANNELS parameters are currently defined.
All audio EXT-X-MEDIA tags SHOULD have a CHANNELS attribute. If a
Multivariant Playlist contains two Renditions with the same NAME
encoded with the same codec but a different number of channels,
then the CHANNELS attribute is REQUIRED; otherwise, it is
OPTIONAL.
The LANGUAGE and ASSOC-LANGUAGE attributes can be used, for example,
to link Norwegian Renditions that use different spoken and written
languages:
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subtitles",
NAME="Bokmael",AUTOSELECT=YES,LANGUAGE="nb",
ASSOC-LANGUAGE="no",URI="nb-subtitles.m3u8"
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This allows automatic selection of the Bokmael subtitles in this
Media Playlist when the user picks an audio variant in Norwegian.
4.4.6.1.1. Rendition Groups
A set of one or more EXT-X-MEDIA tags with the same GROUP-ID value
and the same TYPE value defines a Group of Renditions. Each member
of the Group MUST be an alternative Rendition of the same content;
otherwise, playback errors can occur.
All EXT-X-MEDIA tags in a Playlist MUST meet the following
constraints:
* All EXT-X-MEDIA tags in the same Group MUST have different NAME
attributes.
* A Group MUST NOT have more than one member with a DEFAULT
attribute of YES.
* Each EXT-X-MEDIA tag with an AUTOSELECT=YES attribute SHOULD have
a combination of LANGUAGE [RFC5646], ASSOC-LANGUAGE, FORCED, and
CHARACTERISTICS attributes that is distinct from those of other
AUTOSELECT=YES members of its Group.
A Playlist MAY contain multiple Groups of the same TYPE in order to
provide multiple encodings of that media type. If it does so, each
Group of the same TYPE MUST have the same set of members, and each
corresponding member MUST have identical attributes with the
exception of the URI and CHANNELS attributes.
Each member in a Group of Renditions MAY have a different sample
format. For example, an English Rendition can be encoded with AC-3
5.1 while a Spanish Rendition is encoded with AAC stereo. However,
any EXT-X-STREAM-INF tag (Section 4.4.6.2) or
EXT-X-I-FRAME-STREAM-INF tag (Section 4.4.6.3) that references such a
Group MUST have a CODECS attribute that lists every sample format
present in any Rendition in the Group, or client playback failures
can occur. In the example above, the CODECS attribute would include
"ac-3,mp4a.40.2".
4.4.6.2. EXT-X-STREAM-INF
The EXT-X-STREAM-INF tag specifies a Variant Stream, which is a set
of Renditions that can be combined to play the presentation. The
attributes of the tag provide information about the Variant Stream.
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The URI line that follows the EXT-X-STREAM-INF tag specifies a Media
Playlist that carries a Rendition of the Variant Stream. The URI
line is REQUIRED. Clients that do not support multiple video
Renditions SHOULD play this Rendition.
Its format is:
#EXT-X-STREAM-INF:<attribute-list>
<URI>
The following attributes are defined:
BANDWIDTH
The value is a decimal-integer of bits per second. It represents
the peak segment bit rate of the Variant Stream.
If all the Media Segments in a Variant Stream have already been
created, the BANDWIDTH value MUST be the largest sum of peak
segment bit rates that is produced by any playable combination of
Renditions. (For a Variant Stream with a single Media Playlist,
this is just the peak segment bit rate of that Media Playlist.)
An inaccurate value can cause playback stalls or prevent clients
from playing the variant.
If the Multivariant Playlist is to be made available before all
Media Segments in the presentation have been encoded, the
BANDWIDTH value SHOULD be the BANDWIDTH value of a representative
period of similar content, encoded using the same settings.
Every EXT-X-STREAM-INF tag MUST include the BANDWIDTH attribute.
AVERAGE-BANDWIDTH
The value is a decimal-integer of bits per second. It represents
the average segment bit rate of the Variant Stream.
If all the Media Segments in a Variant Stream have already been
created, the AVERAGE-BANDWIDTH value MUST be the largest sum of
average segment bit rates that is produced by any playable
combination of Renditions. (For a Variant Stream with a single
Media Playlist, this is just the average segment bit rate of that
Media Playlist.) An inaccurate value can cause playback stalls or
prevent clients from playing the variant.
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If the Multivariant Playlist is to be made available before all
Media Segments in the presentation have been encoded, the AVERAGE-
BANDWIDTH value SHOULD be the AVERAGE-BANDWIDTH value of a
representative period of similar content, encoded using the same
settings.
The AVERAGE-BANDWIDTH attribute is OPTIONAL.
SCORE
The value is a positive decimal-floating-point number. It is an
abstract, relative measure of the playback quality-of-experience
of the Variant Stream.
The value can be based on any metric or combination of metrics
that can be consistently applied to all Variant Streams. The
value SHOULD consider all media in the Variant Stream, including
video, audio and subtitles. A Variant Stream with a SCORE
attribute MUST be considered by the Playlist author to be more
desirable than any Variant Stream with a lower SCORE attribute in
the same Multivariant Playlist.
The SCORE attribute is OPTIONAL, but if any Variant Stream
contains the SCORE attribute, then all Variant Streams in the
Multivariant Playlist SHOULD have a SCORE attribute. See
Section 6.3.1 for more information.
CODECS
The value is a quoted-string containing a comma-separated list of
formats, where each format specifies a media sample type that is
present in one or more Renditions specified by the Variant Stream.
Valid format identifiers are those in the ISO Base Media File
Format Name Space defined by "The 'Codecs' and 'Profiles'
Parameters for "Bucket" Media Types" [RFC6381].
For example, a stream containing AAC low complexity (AAC-LC) audio
and H.264 Main Profile Level 3.0 video would have a CODECS value
of "mp4a.40.2,avc1.4d401e".
Note that if a Variant Stream specifies one or more Renditions
that include IMSC subtitles, the CODECS attribute MUST indicate
this with a format identifier such as "stpp.ttml.im1t".
Every EXT-X-STREAM-INF tag SHOULD include a CODECS attribute.
SUPPLEMENTAL-CODECS
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The SUPPLEMENTAL-CODECS attribute describes media samples with
both a backward-compatible base layer and a newer enhancement
layer. The base layers are specified in the CODECS attribute and
the enhancement layers are specified by the SUPPLEMENTAL-CODECS
attribute.
The value is a quoted-string containing a comma-separated list of
elements, where each element specifies an enhancement layer media
sample type that is present in one or more Renditions specified by
the Variant Stream.
Each element is a slash-separated list of fields. The first field
must be a valid CODECS format. If more than one field is present,
the remaining fields must be compatibility brands [MP4RA] that
pertain to that codec's bitstream.
Each member of SUPPLEMENTAL-CODECS must have its base layer codec
declared in the CODECS attribute.
For example, a stream containing Dolby Vision 8.4 content might
have a CODECS attribute including "hvc1.2.4.L153.b0", and a
SUPPLEMENTAL-CODECS attribute including "dvh1.08.07/db4h".
The SUPPLEMENTAL-CODECS attribute is OPTIONAL.
RESOLUTION
The value is a decimal-resolution describing the optimal pixel
resolution at which to display all the video in the Variant
Stream.
The RESOLUTION attribute is OPTIONAL but is recommended if the
Variant Stream includes video.
FRAME-RATE
The value is a decimal-floating-point describing the maximum frame
rate for all the video in the Variant Stream, rounded to three
decimal places.
The FRAME-RATE attribute is OPTIONAL but is recommended if the
Variant Stream includes video. The FRAME-RATE attribute SHOULD be
included if any video in a Variant Stream exceeds 30 frames per
second.
HDCP-LEVEL
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The value is an enumerated-string; valid strings are TYPE-0, TYPE-
1, and NONE. This attribute is advisory. A value of TYPE-0
indicates that the Variant Stream could fail to play unless the
output is protected by High-bandwidth Digital Content Protection
(HDCP) Type 0 [HDCP] or equivalent. A value of TYPE-1 indicates
that the Variant Stream could fail to play unless the output is
protected by HDCP Type 1 or equivalent. A value of NONE indicates
that the content does not require output copy protection.
Encrypted Variant Streams with different HDCP levels SHOULD use
different media encryption keys.
The HDCP-LEVEL attribute is OPTIONAL. It SHOULD be present if any
content in the Variant Stream will fail to play without HDCP.
Clients without output copy protection SHOULD NOT load a Variant
Stream with an HDCP-LEVEL attribute unless its value is NONE.
ALLOWED-CPC
The ALLOWED-CPC attribute allows a server to indicate that the
playback of a Variant Stream containing encrypted Media Segments
is to be restricted to devices that guarantee a certain level of
content protection robustness. Its value is a quoted-string
containing a comma-separated list of entries. Each entry consists
of a KEYFORMAT attribute value followed by a colon character (:)
followed by a sequence of Content Protection Configuration (CPC)
Labels separated by slash (/) characters. Each CPC Label is a
string containing characters from the set [A..Z], [0..9], and '-'.
For example: ALLOWED-CPC="com.example.drm1:SMART-TV/PC,
com.example.drm2:HW"
A CPC Label identifies a class of playback device that implements
the KEYFORMAT with a certain level of content protection
robustness. Each KEYFORMAT can define its own set of CPC Labels.
The "identity" KEYFORMAT does not define any labels. A KEYFORMAT
that defines CPC Labels SHOULD also specify its robustness
requirements in a secure manner in each key response.
A client MAY play the Variant Stream if it implements one of the
listed KEYFORMAT schemes with content protection robustness that
matches one or more of the CPC Labels in the list. If it does not
match any of the CPC Labels then it SHOULD NOT attempt to play the
Variant Stream.
The ALLOWED-CPC attribute is OPTIONAL. If it is not present or
does not contain a particular KEYFORMAT then all clients that
support that KEYFORMAT MAY play the Variant Stream.
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VIDEO-RANGE
The value is an enumerated-string; valid strings are SDR, HLG and
PQ.
The value MUST be SDR if the video in the Variant Stream is
encoded using one of the following reference opto-electronic
transfer characteristic functions specified by the
TransferCharacteristics code point: [CICP] 1, 6, 13, 14, 15. Note
that different TransferCharacteristics code points can use the
same transfer function.
The value MUST be HLG if the video in the Variant Stream is
encoded using a reference opto-electronic transfer characteristic
function specified by the TransferCharacteristics code point 18,
or consists of such video mixed with video qualifying as SDR (see
above).
The value MUST be PQ if the video in the Variant Stream is encoded
using a reference opto-electronic transfer characteristic function
specified by the TransferCharacteristics code point 16, or
consists of such video mixed with video qualifying as SDR or HLG
(see above).
This attribute is OPTIONAL. Its absence implies a value of SDR.
Clients that do not recognize the attribute value SHOULD NOT
select the Variant Stream.
STABLE-VARIANT-ID
The value is a quoted-string which is a stable identifier for the
URI within the Multivariant Playlist. All characters in the
quoted-string MUST be from the following set: [a..z], [A..Z],
[0..9], '+', '/', '=', '.', '-', and '_'. This attribute is
OPTIONAL.
The STABLE-VARIANT-ID allows the URI of the Variant Stream to
change between two distinct downloads of the Multivariant
Playlist. IDs are matched using a byte-for-byte comparison.
All EXT-X-STREAM-INF tags in a Multivariant Playlist with the same
URI value SHOULD use the same STABLE-VARIANT-ID.
AUDIO
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The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the
Multivariant Playlist whose TYPE attribute is AUDIO. It indicates
the set of audio Renditions that SHOULD be used when playing the
presentation. See Section 4.4.6.2.1.
The AUDIO attribute is OPTIONAL.
VIDEO
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the
Multivariant Playlist whose TYPE attribute is VIDEO. It indicates
the set of video Renditions that SHOULD be used when playing the
presentation. See Section 4.4.6.2.1.
The VIDEO attribute is OPTIONAL.
SUBTITLES
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the
Multivariant Playlist whose TYPE attribute is SUBTITLES. It
indicates the set of subtitle Renditions that can be used when
playing the presentation. See Section 4.4.6.2.1.
The SUBTITLES attribute is OPTIONAL.
CLOSED-CAPTIONS
The value can be either a quoted-string or an enumerated-string
with the value NONE. If the value is a quoted-string, it MUST
match the value of the GROUP-ID attribute of an EXT-X-MEDIA tag
elsewhere in the Playlist whose TYPE attribute is CLOSED-CAPTIONS,
and it indicates the set of closed-caption Renditions that can be
used when playing the presentation. See Section 4.4.6.2.1.
If the value is the enumerated-string value NONE, all EXT-X-
STREAM-INF tags MUST have this attribute with a value of NONE,
indicating that there are no closed captions in any Variant Stream
in the Multivariant Playlist. Having closed captions in one
Variant Stream but not another can trigger playback
inconsistencies.
The CLOSED-CAPTIONS attribute is OPTIONAL.
PATHWAY-ID
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The value is a quoted-string. It indicates that the Variant
Stream belongs to the identified Content Steering (Section 7)
Pathway. This attribute is OPTIONAL. Its absence indicates that
the Variant Stream belongs to the default Pathway ".", so every
Variant Stream can be associated with a named Pathway.
A Content Provider SHOULD provide all Rendition Groups on all
Pathways. A Variant Stream belonging to a particular Pathway
SHOULD use Rendition Group(s) on that Pathway.
4.4.6.2.1. Alternative Renditions
When an EXT-X-STREAM-INF tag contains an AUDIO, VIDEO, SUBTITLES, or
CLOSED-CAPTIONS attribute, it indicates that alternative Renditions
of the content are available for playback of that Variant Stream.
When defining alternative Renditions, the following constraints MUST
be met to prevent client playback errors:
* All playable combinations of Renditions associated with an EXT-X-
STREAM-INF tag MUST have an aggregate bandwidth less than or equal
to the BANDWIDTH attribute of the EXT-X-STREAM-INF tag.
* If an EXT-X-STREAM-INF tag contains a RESOLUTION attribute and a
VIDEO attribute, then every alternative video Rendition MUST have
an optimal display resolution matching the value of the RESOLUTION
attribute.
* Every alternative Rendition associated with an EXT-X-STREAM-INF
tag MUST meet the constraints for a Variant Stream described in
Section 6.2.4.
The URI attribute of the EXT-X-MEDIA tag is REQUIRED if the media
type is SUBTITLES, but OPTIONAL if the media type is VIDEO or AUDIO.
If the media type is VIDEO or AUDIO, a missing URI attribute
indicates that the media data for this Rendition is included in the
Media Playlist of any EXT-X-STREAM-INF tag referencing this EXT-
X-MEDIA tag. If the media TYPE is AUDIO and the URI attribute is
missing, clients MUST assume that the audio data for this Rendition
is present in every video Rendition specified by the EXT-X-STREAM-INF
tag.
The URI attribute of the EXT-X-MEDIA tag MUST NOT be included if the
media type is CLOSED-CAPTIONS.
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4.4.6.3. EXT-X-I-FRAME-STREAM-INF
The EXT-X-I-FRAME-STREAM-INF tag identifies a Media Playlist file
containing the I-frames of a multimedia presentation. It stands
alone, in that it does not apply to a particular URI in the
Multivariant Playlist. Its format is:
#EXT-X-I-FRAME-STREAM-INF:<attribute-list>
All attributes defined for the EXT-X-STREAM-INF tag (Section 4.4.6.2)
are also defined for the EXT-X-I-FRAME-STREAM-INF tag, except for the
FRAME-RATE, AUDIO, SUBTITLES, and CLOSED-CAPTIONS attributes. In
addition, the following attribute is defined:
URI
The value is a quoted-string containing a URI that identifies the
I-frame Media Playlist file. That Playlist file MUST contain an
EXT-X-I-FRAMES-ONLY tag.
Every EXT-X-I-FRAME-STREAM-INF tag MUST include a BANDWIDTH attribute
and a URI attribute.
The provisions in Section 4.4.6.2.1 also apply to EXT-X-I-FRAME-
STREAM-INF tags with a VIDEO attribute.
A Multivariant Playlist that specifies alternative VIDEO Renditions
and I-frame Playlists SHOULD include an alternative I-frame VIDEO
Rendition for each regular VIDEO Rendition, with the same NAME and
LANGUAGE attributes.
4.4.6.4. EXT-X-SESSION-DATA
The EXT-X-SESSION-DATA tag allows arbitrary session data to be
carried in a Multivariant Playlist.
Its format is:
#EXT-X-SESSION-DATA:<attribute-list>
The following attributes are defined:
DATA-ID
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The value of DATA-ID is a quoted-string that identifies a
particular data value. The DATA-ID SHOULD conform to a reverse
DNS naming convention, such as "com.example.movie.title"; however,
there is no central registration authority, so Playlist authors
SHOULD take care to choose a value that is unlikely to collide
with others. This attribute is REQUIRED.
VALUE
VALUE is a quoted-string. It contains the data identified by
DATA-ID. If the LANGUAGE is specified, VALUE SHOULD contain a
human-readable string written in the specified language.
URI
The value is a quoted-string containing a URI. The resource
identified by the URI MUST be formatted as JSON [RFC8259];
otherwise, clients may fail to interpret the resource.
LANGUAGE
The value is a quoted-string containing a language tag [RFC5646]
that identifies the language of the VALUE. This attribute is
OPTIONAL.
Each EXT-X-SESSION-DATA tag MUST contain either a VALUE or URI
attribute, but not both.
A Playlist MAY contain multiple EXT-X-SESSION-DATA tags with the same
DATA-ID attribute. A Playlist MUST NOT contain more than one EXT-X-
SESSION-DATA tag with the same DATA-ID attribute and the same
LANGUAGE attribute.
4.4.6.5. EXT-X-SESSION-KEY
The EXT-X-SESSION-KEY tag allows encryption keys from Media Playlists
to be specified in a Multivariant Playlist. This allows the client
to preload these keys without having to read the Media Playlist(s)
first.
Its format is:
#EXT-X-SESSION-KEY:<attribute-list>
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All attributes defined for the EXT-X-KEY tag (Section 4.4.4.4) are
also defined for the EXT-X-SESSION-KEY, except that the value of the
METHOD attribute MUST NOT be NONE. If an EXT-X-SESSION-KEY is used,
the values of the METHOD, KEYFORMAT, and KEYFORMATVERSIONS attributes
MUST match any EXT-X-KEY with the same URI value.
EXT-X-SESSION-KEY tags SHOULD be added if multiple Variant Streams or
Renditions use the same encryption keys and formats. An EXT-X-
SESSION-KEY tag is not associated with any particular Media Playlist.
A Multivariant Playlist MUST NOT contain more than one EXT-X-SESSION-
KEY tag with the same METHOD, URI, IV, KEYFORMAT, and
KEYFORMATVERSIONS attribute values.
The EXT-X-SESSION-KEY tag is optional.
4.4.6.6. EXT-X-CONTENT-STEERING
The EXT-X-CONTENT-STEERING tag allows a server to provide a Content
Steering (Section 7) Manifest. It is OPTIONAL. It MUST NOT appear
more than once in a Multivariant Playlist. Its format is:
#EXT-X-CONTENT-STEERING:<attribute-list>
The following attributes are defined:
SERVER-URI
The value is a quoted-string containing a URI to a Steering
Manifest (Section 7.1). It MAY contain an asset identifier if the
Steering Server requires it to produce the Steering Manifest. It
MAY use the "data" URI scheme to provide the manifest in-line in
the Multivariant Playlist; in that case, subsequent manifest
reloads MAY be redirected to a remote Steering Server using the
RELOAD-URI parameter (see Section 7.1). This attribute is
REQUIRED.
PATHWAY-ID
The value is a quoted-string that identifies the Pathway that MUST
be applied by any client that supports Content Steering (see
Section 7.4) until the initial Steering Manifest has been
obtained. Its value MUST be a legal Pathway ID according to
Section 7.1 that is specified by the PATHWAY-ID attribute of one
or more Variant Streams in the Multivariant Playlist. This
attribute is OPTIONAL.
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5. Key Files
5.1. Structure of Key Files
An EXT-X-KEY tag with a URI attribute identifies a Key file. A Key
file contains a cipher key that can decrypt Media Segments in the
Playlist.
[AES_128] encryption uses 16-octet keys. If the KEYFORMAT of an EXT-
X-KEY tag is "identity", the Key file is a single packed array of 16
octets in binary format.
5.2. IV for AES-128
[AES_128] REQUIRES the same 16-octet IV to be supplied when
encrypting and decrypting. Varying this IV increases the strength of
the cipher.
An IV attribute on an EXT-X-KEY tag with a KEYFORMAT of "identity"
specifies an IV that can be used when decrypting Media Segments
encrypted with that Key file. IV values for AES-128 are 128-bit
numbers.
An EXT-X-KEY tag with a KEYFORMAT of "identity" that does not have an
IV attribute indicates that the Media Sequence Number is to be used
as the IV when decrypting a Media Segment, by putting its big-endian
binary representation into a 16-octet (128-bit) buffer and padding
(on the left) with zeros.
6. Client/Server Responsibilities
6.1. Introduction
This section describes how the server generates the Playlist and
Media Segments and how the client should download them for playback.
6.2. Server Responsibilities
6.2.1. General Server Responsibilities
The production of the source media is outside the scope of this
document, which simply presumes a source of continuous encoded media
containing the presentation.
The server MUST divide the source media into individual Media
Segments whose duration (when rounded to a whole second) is less than
or equal to the Target Duration. Segments longer than that can
trigger playback stalls and other errors.
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The server SHOULD attempt to divide the source media at points that
support effective decode of individual Media Segments, such as on
packet and key frame boundaries.
The server MUST create a URI for every Media Segment that enables its
clients to obtain the segment data. If a server supports partial
loading of resources (e.g., via HTTP Range requests), it MAY specify
segments as sub-ranges of larger resources using the EXT-X-BYTERANGE
tag.
The absence of media data (due to, for example, the temporary
unavailability of an encoder) SHOULD be signaled by adding one or
more Media Segments to the Playlist whose Segment durations add up to
the duration of absent media; these Media Segments MUST have EXT-
X-GAP tags applied to them. Similarly, such Partial Segments MUST
have a GAP=YES attribute. Attempting to download these segments MAY
produce an error, such as HTTP 404 or 410.
A Media Segment MUST be available for immediate download at the full
speed of the link to the Client when it is added to a Playlist unless
it has been marked with an EXT-X-GAP tag; otherwise playback errors
can occur. Once download starts, its transfer rate SHOULD NOT be
constrained by the segment production process.
A Partial Segment MUST be similarly available at the time it is added
to a Playlist.
HTTP servers SHOULD transfer text files -- such as Playlists and
WebVTT segments -- using the "gzip" Content-Encoding if the client
indicates that it is prepared to accept it.
The server must create a Media Playlist file (Section 4) that
contains a URI for each Media Segment that the server wishes to make
available, in the order in which they are to be played.
The value of the EXT-X-VERSION tag (Section 4.4.1.2) SHOULD NOT be
greater than what is required for the tags and attributes in the
Playlist (see Section 8).
Changes to the Playlist file MUST be made atomically from the point
of view of the clients, or playback errors MAY occur.
The server MUST NOT change the Media Playlist file, except to:
Append lines to it (Section 6.2.1).
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Remove Media Segment URIs from the Playlist in the order that they
appear, along with any tags that apply only to those segments
(Section 6.2.2).
Remove Media Metadata tags that no longer apply to the
presentation (Section 6.2.1).
Remove EXT-X-PART tags no longer at the live edge (Section 6.2.2).
Increment the value of the EXT-X-MEDIA-SEQUENCE or EXT-X-
DISCONTINUITY-SEQUENCE tags (Section 6.2.2).
Add an EXT-X-ENDLIST tag to the Playlist (Section 6.2.1).
A Media Playlist has further constraints on its updates if it
contains an EXT-X-PLAYLIST-TYPE tag. An EXT-X-PLAYLIST-TYPE tag with
a value of VOD indicates that the Playlist file MUST NOT change. An
EXT-X-PLAYLIST-TYPE tag with a value of EVENT indicates that the
Server MUST NOT change or remove any part of the Playlist file, with
the exception of EXT-X-PART tags and Media Metadata tags as described
above; the Server MAY append lines to the Playlist.
The value of the EXT-X-TARGETDURATION tag in the Media Playlist MUST
NOT change. A typical Target Duration is 6 seconds.
Playlist changes other than those allowed here can trigger playback
errors and inconsistent client behavior.
Each Media Segment in a Media Playlist has an integer Discontinuity
Sequence Number. The Discontinuity Sequence Number can be used in
addition to the timestamps within the media to synchronize Media
Segments across different Renditions.
A segment's Discontinuity Sequence Number is the value of the EXT-X-
DISCONTINUITY-SEQUENCE tag (or zero if none) plus the number of EXT-
X-DISCONTINUITY tags in the Playlist preceding the URI line of the
segment.
The server MAY associate an absolute date and time with a Media
Segment by applying an EXT-X-PROGRAM-DATE-TIME tag to it. This
defines an informative mapping of the (wall-clock) date and time
specified by the tag to the first media timestamp in the segment,
which may be used as a basis for seeking, for display, or for other
purposes. If a server provides this mapping, it SHOULD apply an EXT-
X-PROGRAM-DATE-TIME tag to every segment that has an EXT-
X-DISCONTINUITY tag applied to it.
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The Server MUST NOT add any EXT-X-PROGRAM-DATE-TIME tag to a Playlist
that would cause the mapping between program date and Media Segment
to become ambiguous.
When applied to live content, a reasonable default for the EXT-X-
PROGRAM-DATE-TIME tag is the date and time that the content was
captured (recorded).
The server MUST NOT remove an EXT-X-DATERANGE tag from a Playlist if
any date in the range maps to a Media Segment in the Playlist.
The server MUST NOT reuse the ID attribute value of an EXT-
X-DATERANGE tag for any new Date Range in the same Playlist.
Once the Following Range of a Date Range with an END-ON-NEXT=YES
attribute is added to a Playlist, the Server MUST NOT subsequently
add a Date Range with the same CLASS attribute whose START-DATE is
between that of the END-ON-NEXT=YES range and its Following Range.
For Date Ranges with a PLANNED-DURATION attribute, the Server SHOULD
signal the actual end of the range once it has been established. It
can do so by adding another EXT-X-DATERANGE tag with the same ID
attribute value and either a DURATION or an END-DATE attribute or, if
the Date Range has an END-ON-NEXT=YES attribute, by adding a
Following Range.
If the Media Playlist contains the final Media Segment of the
presentation, then the Playlist file MUST contain the EXT-X-ENDLIST
tag; this allows clients to minimize unproductive Playlist reloads.
If a Media Playlist does not contain the EXT-X-ENDLIST tag, the
server MUST make a new version of the Playlist file available that
contains at least one new Media Segment. It MUST be made available
no later than 1.5 times the Target Duration after the previous time
the Playlist was updated with a Media Segment. This allows clients
to utilize the network efficiently.
If a Media Playlist without an EXT-X-ENDLIST tag contains Partial
Segments, the Server MUST add a new Partial Segment to the Playlist
within one Part Target Duration after it added the previous Partial
Segment.
If the server wishes to remove an entire presentation, it SHOULD
provide a clear indication to clients that the Playlist file is no
longer available (e.g., with an HTTP 404 or 410 response). It MUST
ensure that all Media Segments in the Playlist file remain available
to clients for at least the duration of the Playlist file at the time
of removal to prevent interruption of in-progress playback.
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6.2.2. Live Playlists
The server MAY limit the availability of Media Segments by removing
Media Segments from the Playlist file (Section 6.2.1). If Media
Segments are to be removed, the Playlist file MUST contain an EXT-X-
MEDIA-SEQUENCE tag. Its value MUST be incremented by 1 for every
Media Segment that is removed from the Playlist file; it MUST NOT
decrease or wrap. Clients can malfunction if each Media Segment does
not have a consistent, unique Media Sequence Number.
EXT-X-PART tags SHOULD be removed from the Playlist after they are
greater than three Target Durations from the end of the Playlist.
Clients MUST be able to download the Partial Segment for at least
three Target Durations after the EXT-X-PART tag is removed from the
Playlist.
Media Segments and EXT-X-PART tags MUST be removed from the Playlist
in the order that they appear in the Playlist; otherwise, client
playback can malfunction.
The server MUST NOT remove a Media Segment from a Playlist file
without an EXT-X-ENDLIST tag if that would produce a Playlist whose
duration is less than three times the Target Duration. Doing so can
trigger playback stalls.
The Availability Duration of a Media Segment is the duration of the
segment plus the duration of the longest-duration Playlist
distributed by the server containing that segment. If the server
removes a Media Segment URI from a Playlist that contains an EXT-
X-ENDLIST tag, clients MUST be able to download the corresponding
Media Segment until the time of removal plus the segment's
Availability Duration. If the server removes a Media Segment URI
from a Playlist that does not contain an EXT-X-ENDLIST tag, clients
MUST be able to download the segment until the time at which it first
appeared in the Playlist plus the segment's Availability Duration.
If the server wishes to remove segments from a Media Playlist
containing an EXT-X-DISCONTINUITY tag, the Media Playlist MUST
contain an EXT-X-DISCONTINUITY-SEQUENCE tag. Without the EXT-X-
DISCONTINUITY-SEQUENCE tag, it can be impossible for a client to
locate corresponding segments between Renditions.
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If the server removes an EXT-X-DISCONTINUITY tag from the Media
Playlist, it MUST increment the value of the EXT-X-DISCONTINUITY-
SEQUENCE tag so that the Discontinuity Sequence Numbers of the
segments still in the Media Playlist remain unchanged. The value of
the EXT-X-DISCONTINUITY-SEQUENCE tag MUST NOT decrease or wrap.
Clients can malfunction if each Media Segment does not have a
consistent Discontinuity Sequence Number.
If a server plans to remove a Media Segment after it is delivered to
clients over HTTP, it SHOULD ensure that the HTTP response contains
an Expires header that reflects the planned time-to-live.
A Live Playlist MUST NOT contain the EXT-X-PLAYLIST-TYPE tag, as no
value of that tag allows Media Segments to be removed.
6.2.3. Encrypting Media Segments
Media Segments MAY be encrypted. Every encrypted Media Segment MUST
have an EXT-X-KEY tag (Section 4.4.4.4) applied to it with a URI that
the client can use to obtain a Key file (Section 5) containing the
decryption key.
A Media Segment can only be encrypted with one encryption METHOD,
using one encryption key and IV. However, a server MAY offer
multiple ways to retrieve that key by providing multiple EXT-X-KEY
tags, each with a different KEYFORMAT attribute value.
The server MAY set the HTTP Expires header in the key response to
indicate the duration for which the key can be cached.
Any unencrypted Media Segment in a Playlist MUST be in the scope of
an EXT-X-KEY tag that specifies an encryption METHOD of NONE or
precedes the first EXT-X-KEY tag. Otherwise, the client will
misinterpret those segments as encrypted.
If the encryption METHOD is AES-128 and the Playlist does not contain
the EXT-X-I-FRAMES-ONLY tag, AES encryption as described in
Section 4.4.4.4 SHALL be applied to individual Media Segments.
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If the encryption METHOD is AES-128 and the Playlist contains an EXT-
X-I-FRAMES-ONLY tag, the entire resource MUST be encrypted using
AES-128 CBC with PKCS7 padding [RFC5652]. Encryption MAY be
restarted on 16-byte block boundaries, unless the first block
contains an I-frame. The IV used for encryption MUST be either the
Media Sequence Number of the Media Segment or the value of the IV
attribute of the EXT-X-KEY tag, as described in Section 5.2. These
constraints allow a client to load and decrypt individual I-frames
specified as sub-ranges of regular encrypted Media Segments, and
their Media Initialization Sections.
If the encryption METHOD indicates Sample Encryption, media samples
MAY be encrypted prior to encapsulation in a Media Segment.
The server MUST NOT remove an EXT-X-KEY tag from the Playlist file if
it applies to any Media Segment in the Playlist file, or clients who
subsequently load that Playlist will be unable to decrypt those Media
Segments.
6.2.4. Providing Variant Streams
A server MAY offer multiple Media Playlist files to provide different
encodings of the same presentation. If it does so, it SHOULD provide
a Multivariant Playlist file that lists each Variant Stream to allow
clients to switch between encodings dynamically.
Multivariant Playlists describe regular Variant Streams with EXT-X-
STREAM-INF tags and I-frame Variant Streams with EXT-X-I-FRAME-
STREAM-INF tags.
If an EXT-X-STREAM-INF tag or EXT-X-I-FRAME-STREAM-INF tag contains
the CODECS attribute, the attribute value MUST include every media
format [RFC6381] present in any Media Segment in any of the
Renditions specified by the Variant Stream.
The server MUST meet the following constraints when producing Variant
Streams in order to allow clients to switch between them seamlessly:
Each Variant Stream MUST present the same content.
Matching content in Variant Streams MUST have matching timestamps.
This allows clients to synchronize the media.
Matching content in Variant Streams MUST have matching
Discontinuity Sequence Numbers (see Section 4.4.3.3).
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Each Media Playlist in each Variant Stream MUST have the same
Target Duration. The only exceptions are SUBTITLES Renditions and
Media Playlists containing an EXT-X-I-FRAMES-ONLY tag, which MAY
have different Target Durations if they have an EXT-X-PLAYLIST-
TYPE of VOD.
Content that appears in a Media Playlist of one Variant Stream but
not in another MUST appear either at the beginning or at the end
of the Media Playlist file and MUST NOT be longer than the
smallest Target Duration declared in any Media Playlist in the
Multivariant Playlist.
If any Media Playlists have an EXT-X-PLAYLIST-TYPE tag, all Media
Playlists MUST have an EXT-X-PLAYLIST-TYPE tag with the same
value.
If the Playlist contains an EXT-X-PLAYLIST-TYPE tag with the value
of VOD, the first segment of every Media Playlist in every Variant
Stream MUST start at the same media timestamp.
If any Media Playlist in a Multivariant Playlist contains an EXT-
X-PROGRAM-DATE-TIME tag, then all Media Playlists in that
Multivariant Playlist MUST contain EXT-X-PROGRAM-DATE-TIME tags
with consistent mappings of date and time to media timestamps.
If any Playlist contains Date Ranges, then at least one Playlist
in any playable combination of Renditions of any Variant Stream
MUST contain Date Ranges. Any Playlist with Date Ranges MUST
contain the same set of Date Ranges as the others that do. The
EXT-X-DATERANGE tags of corresponding Date Ranges MUST have the
same ID attribute value and contain the same set of attribute/
value pairs.
If any Media Playlist in a Multivariant Playlist contains an EXT-
X-SERVER-CONTROL tag, then all Media Playlists in that
Multivariant Playlist MUST contain that tag, with the same
attributes and values.
In addition, for broadest compatibility, Variant Streams SHOULD
contain the same encoded audio bitstream. This allows clients to
switch between Variant Streams without audible glitching.
The rules for Variant Streams also apply to alternative Renditions
(see Section 4.4.6.2.1).
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6.2.5. Delivery Directives Interface
A server MAY provide a set of services to its clients by implementing
support for Delivery Directives. Delivery Directives are transmitted
by the Client to the Server as Query Parameters in Playlist request
URIs.
Servers advertise the availability of Delivery Directives using the
EXT-X-SERVER-CONTROL tag (Section 4.4.3.8).
Currently-defined Delivery Directives are _HLS_skip, _HLS_msn and
_HLS_part.
6.2.5.1. Playlist Delta Updates
Live presentations involve frequent Playlist downloads. When
Playlists are large and a Client already has the previous version,
the transfer cost can be reduced considerably by sending only the
newest information in response to a Playlist update request.
A Server advertises support for Playlist Delta Updates that skip
older Media Segments by adding the CAN-SKIP-UNTIL attribute to the
EXT-X-SERVER-CONTROL tag. A Server can also offer support for
Playlist Delta Updates that skip older EXT-X-DATERANGE tags by adding
the CAN-SKIP-DATERANGES attribute to the EXT-X-SERVER-CONTROL tag.
When a Server receives a request for a Playlist containing the CAN-
SKIP-UNTIL attribute but no EXT-X-ENDLIST tag, and the requested URI
contains an _HLS_skip directive whose value is YES or v2, it MUST
respond with a Playlist Delta Update.
The Playlist Delta Update is a version of the Playlist in which Media
Segments that are further from the end of the last (Parent) Media
Segment in the Playlist than the Skip Boundary (Section 4.4.3.8), as
well as their associated tags, are replaced by an EXT-X-SKIP tag
(Section 4.4.5.2).
When the _HLS_skip directive has a value of v2, the Playlist Delta
Update additionally MUST NOT contain EXT-X-DATERANGE tags that were
added to the Playlist more than CAN-SKIP-UNTIL seconds before the
Playlist request. The RECENTLY-REMOVED-DATERANGES attribute of the
EXT-X-SKIP tag MUST list the date ranges that were removed from the
Playlist within CAN-SKIP-UNTIL seconds of the Playlist request.
All tags that were not skipped MUST remain in the Playlist Delta
Update.
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A Server MUST ignore the _HLS_skip directive if the Playlist does not
contain the CAN-SKIP-UNTIL attribute, or if it contains an EXT-
X-ENDLIST tag.
6.2.5.2. Blocking Playlist Reload
A Server MAY offer Blocking Playlist Reloads, which enable immediate
client discovery of Playlist updates as an alternative to polling.
A Server advertises support for Blocking Playlist Reload by adding
the CAN-BLOCK-RELOAD=YES attribute to the EXT-X-SERVER-CONTROL tag.
A Client requests a Blocking Playlist Reload using an _HLS_msn
directive with a decimal-integer value M. When the Playlist URI
contains an _HLS_msn directive and no _HLS_part directive, the Server
MUST defer responding to the request until the Playlist contains a
Media Segment with a Media Sequence Number of M or later or it
responds with an error.
The Playlist URI MAY also contain an _HLS_part directive with a
decimal-integer value N. When the Playlist URI contains both an
_HLS_msn directive and an _HLS_part directive, the Server MUST defer
responding to the request until the Playlist contains the Partial
Segment with Part Index N and with a Media Sequence Number of M or
later or it responds with an error.
If the Client requests a Part Index greater than that of the final
Partial Segment of the Parent Segment, the Server MUST treat the
request as one for Part Index 0 of the following Parent Segment.
The Server MUST deliver the entire Playlist, even if the requested
Media Segment is not the last one in the Playlist, and even if it is
no longer in the Playlist.
A Server MUST ignore _HLS_msn and _HLS_part if the Playlist contains
an EXT-X-ENDLIST tag.
If the _HLS_msn is greater than the Media Sequence Number of the last
Media Segment in the current Playlist plus two, or if the _HLS_part
exceeds the last Partial Segment in the current Playlist by the
Advance Part Limit, then the server SHOULD immediately return Bad
Request, such as HTTP 400. The Advance Part Limit is three divided
by the Part Target Duration if the Part Target Duration is less than
one second, or three otherwise.
If the Playlist URI contains an _HLS_part directive but no _HLS_msn
directive, the Server MUST return Bad Request, such as HTTP 400.
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A Server that cannot provide the requested Playlist after blocking
for more than three Target Durations SHOULD return Service
Unavailable, such as HTTP 503.
6.2.6. Providing Preload Hints
The Server MAY add EXT-X-PRELOAD-HINT tags (Section 4.4.5.3) to the
Playlist to allow Clients playing the stream to request upcoming
resources in advance.
A hinted resource MUST be available for request when its EXT-X-
PRELOAD-HINT tag is added to the Playlist.
When processing requests for a URI or a byte range of a URI that
includes one or more Partial Segments that are not yet completely
available to be sent - such as requests made in response to an EXT-X-
PRELOAD-HINT tag - the server MUST refrain from transmitting any
bytes belonging to a Partial Segment until all bytes of that Partial
Segment can be transmitted at the full speed of the link to the
client. If the requested range includes more than one Partial
Segment then the server MUST enforce this delivery guarantee for each
Partial Segment in turn. This enables the client to perform accurate
Adaptive Bit Rate (ABR) measurements.
The Server SHOULD NOT hint a byte range that it does not expect its
clients to require in the near term.
The server SHOULD respond with "Not Found" (such as HTTP 404) to a
request for a resource that it cannot find and that is not specified
by an EXT-X-PRELOAD-HINT tag in an active Media Playlist.
A server MAY choose not to publish previously-hinted resources if the
planned segmentation changes, such as the case of early return from
an ad. The server SHOULD respond to client requests for those
resources with "Not Found" (such as HTTP 404).
If a Partial Segment is created as a sub-range of a larger resource
and its length is not known at the time that its hint is added to the
Playlist, the BYTERANGE-LENGTH attribute SHOULD be omitted. The
BYTERANGE-OFFSET SHOULD indicate the Partial Segment's starting
offset into the larger resource.
The Server SHOULD NOT add more than one EXT-X-PRELOAD-HINT tag with
the same TYPE to a Playlist.
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6.3. Client Responsibilities
6.3.1. General Client Responsibilities
How the client obtains the URI to the Playlist file is outside the
scope of this document; it is presumed to have done so.
The client obtains the Playlist file from the URI. If the Playlist
file so obtained is a Multivariant Playlist, the client can select a
Variant Stream to load from the Multivariant Playlist.
Clients MUST ensure that loaded Playlists comply with Section 4 and
that the EXT-X-VERSION tag, if present, specifies a protocol version
supported by the client; if either check fails, the client MUST NOT
attempt to use the Playlist, or unintended behavior could occur.
When parsing Playlist elements that are subject to variable
substitution, a Variable Reference whose Variable Name has been
provided by an EXT-X-DEFINE tag that precedes the Variable Reference
MUST be replaced by the corresponding Variable Value. Such
replacements themselves are NOT subject to variable substitution.
When parsing Playlist elements that are subject to variable
substitution, a Variable Reference whose Variable Name has NOT been
provided by an EXT-X-DEFINE tag preceding the Variable Reference MUST
trigger a parsing error.
If any URI element in a Playlist contains an URI scheme that the
client cannot handle, the client MUST stop playback. All clients
MUST support HTTP schemes.
To support forward compatibility, when parsing Playlists, clients
MUST:
* ignore any unrecognized tags.
* ignore any attribute/value pair with an unrecognized
AttributeName.
* ignore any tag containing an attribute/value pair of type
enumerated-string whose AttributeName is recognized but whose
AttributeValue is not recognized, unless the definition of the
attribute says otherwise.
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When identifying playable Renditions, Clients SHOULD consider an
audio Rendition having unrecognized CHANNELS parameters to be
playable if its associated CODECS attribute is supported. However,
an equivalent Rendition with the same audio codec and recognized
CHANNELS parameters SHOULD be preferred if it is present in the
Multivariant Playlist.
When all Variant Streams have a SCORE attribute, the client SHOULD
use the SCORE value to choose a Variant Stream after all other
playability constraints have been applied. If several Variant
Streams have the highest SCORE value then other criteria MAY be used
to chose among them.
Algorithms used by the client to switch between Variant Streams are
beyond the scope of this document.
6.3.2. Loading the Media Playlist File
Every time a Media Playlist is loaded or reloaded from a Playlist
URI, the client MUST determine the next Media Segment to load, as
described in Section 6.3.5, if it intends to play the presentation
normally (i.e., in Playlist order at the nominal playback rate).
If the Media Playlist contains the EXT-X-MEDIA-SEQUENCE tag, the
client SHOULD assume that each Media Segment in it will become
unavailable at the time that the Playlist file was loaded plus the
duration of the Playlist file.
A client MAY use the segment Media Sequence Number to track the
location of a Media Segment within a Playlist when the Playlist is
reloaded.
A client MUST NOT assume that segments with the same Media Sequence
Number in different Variant Streams or Renditions have the same
position in the presentation; Playlists MAY have independent Media
Sequence Numbers. Instead, a client MUST use the relative position
of each segment on the Playlist timeline and its Discontinuity
Sequence Number to locate corresponding segments.
Clients using Delivery Directives (Section 6.2.5) MUST ensure that
all query parameters appear in UTF-8 order within the URI. This
improves Server cache utilization.
A client MUST load the Media Playlist file of every Rendition
selected for playback in order to locate the media specific to that
Rendition. But, to prevent unnecessary load on the server, it SHOULD
NOT load the Playlist file of any other Rendition.
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For some Variant Streams, it is possible to select Renditions that do
not include the Rendition specified by the EXT-X-STREAM-INF tag. As
noted above, the client SHOULD NOT load that Rendition in those
cases.
6.3.3. Playing the Media Playlist File
The client SHALL choose which Media Segment to play first from the
Media Playlist when playback starts. If the EXT-X-ENDLIST tag is not
present and the client intends to play the media normally, the client
SHOULD NOT choose a segment closer to the end of the Playlist than
described by the HOLD-BACK and PART-HOLD-BACK attributes. Doing so
can trigger playback stalls.
Normal playback can be achieved by playing Media Segments or Partial
Segments in the order that they appear in the Playlist. The client
MAY present the available media in any way it wishes, including
normal playback, random access, and trick modes.
The client SHOULD NOT attempt to load Media Segments that have been
marked with an EXT-X-GAP tag, or to load Partial Segments with a
GAP=YES attribute. Instead, clients are encouraged to look for
another Variant Stream of the same Rendition which does not have the
same gap, and play that instead.
The encoding parameters for samples in a Media Segment and across
multiple Media Segments in a Media Playlist SHOULD remain consistent.
However, clients SHOULD deal with encoding changes as they are
encountered, for example, by scaling video content to accommodate a
resolution change. If the Variant Stream includes a RESOLUTION
attribute, clients SHOULD display all video within a rectangle with
the same proportions as that resolution.
Clients SHOULD be prepared to handle multiple tracks of a particular
type (e.g., audio or video). A client with no other preference
SHOULD choose the track with the lowest numerical track identifier
that it can play.
Clients SHOULD ignore private streams inside Transport Streams that
they do not recognize. Private streams can be used to support
different devices with the same stream, although stream authors
SHOULD be sensitive to the additional network load that this imposes.
The client MUST be prepared to reset its parser(s) and decoder(s)
before playing a Media Segment that has an EXT-X-DISCONTINUITY tag
applied to it; otherwise, playback errors can occur.
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The client SHOULD attempt to load Media Segments in advance of when
they will be required for uninterrupted playback to compensate for
temporary variations in latency and throughput.
The client MAY use the value of the EXT-X-PROGRAM-DATE-TIME tag to
display the program origination time to the user. If the value
includes time zone information, the client SHALL take it into
account; if it does not, the client MAY assume the time to be local.
Note that dates in Playlists can refer to when the content was
produced (or to other times), which have no relation to the time of
playback.
If the first EXT-X-PROGRAM-DATE-TIME tag in a Playlist appears after
one or more Media Segment URIs, the client SHOULD extrapolate
backward from that tag (using EXTINF durations and/or media
timestamps) to associate dates with those segments. To associate a
date with any other Media Segment that does not have an EXT-X-
PROGRAM-DATE-TIME tag applied to it directly, the client SHOULD
extrapolate forward from the last EXT-X-PROGRAM-DATE-TIME tag
appearing before that segment in the Playlist.
6.3.4. Reloading the Media Playlist File
The client MUST periodically reload a Media Playlist file to learn
what media is currently available, unless it contains an EXT-X-
PLAYLIST-TYPE tag with a value of VOD, or a value of EVENT and the
EXT-X-ENDLIST tag is also present.
However, the client MUST NOT attempt to reload the Playlist file more
frequently than specified by this section, in order to limit the
collective load on the server.
When a client loads a Playlist file for the first time or reloads a
Playlist file and finds that it has changed since the last time it
was loaded, the client MUST wait for at least the duration of the
last segment in the Playlist before attempting to reload the Playlist
file again, measured from the last time the client began loading the
Playlist file.
If the client reloads a Playlist file and finds that it has not
changed, then it MUST wait for a period of one-half the Target
Duration before retrying. If the Playlist file remains unchanged
when reloaded and it has been at least 1.5 times the Target Duration
since the last time the client loaded a changed Playlist then the
client MAY conclude that the server is not behaving properly and
switch to a different Variant Stream or trigger a playback error.
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After reloading a Media Playlist, the client SHOULD verify that each
Media Segment in it has the same URI (and byte range, if specified)
as the Media Segment with the same Media Sequence Number in the
previous Media Playlist. It SHOULD halt playback if it does not, as
this normally indicates a server error.
In order to reduce server load, the client SHOULD NOT reload the
Playlist files of Variant Streams or alternate Renditions that are
not currently being played. If it decides to switch playback to a
different Variant Stream, it SHOULD stop reloading the Playlist of
the old Variant Stream and begin loading the Playlist of the new
Variant Stream. It can use the EXTINF durations and the constraints
in Section 6.2.4 to determine the approximate location of
corresponding media. Once media from the new Variant Stream has been
loaded, the timestamps in the Media Segments can be used to
synchronize the old and new timelines precisely.
A client MUST NOT attempt to use the Media Sequence Number to
synchronize between streams (see Section 6.3.2).
6.3.5. Determining the Next Segment to Load
The client MUST examine the Media Playlist file every time it is
loaded or reloaded to determine the next Media Segment to load, as
the set of available media MAY have changed.
The first segment to load is generally the segment that the client
has chosen to play first (see Section 6.3.3).
In order to play the presentation normally, the next Media Segment to
load is the one with the lowest Media Sequence Number that is greater
than the Media Sequence Number of the last Media Segment loaded.
6.3.6. Decrypting Encrypted Media Segments
If a Media Playlist file contains an EXT-X-KEY tag that specifies a
Key file URI, the client can obtain that Key file and use the key
inside it to decrypt all Media Segments to which that EXT-X-KEY tag
applies.
A client MUST ignore any EXT-X-KEY tag with an unsupported or
unrecognized KEYFORMAT attribute, to allow for cross-device
addressability. If the Playlist contains a Media Segment to which
only EXT-X-KEY tags with unrecognized or unsupported KEYFORMAT
attributes are applied, playback SHOULD fail.
A client MUST NOT attempt to decrypt any segments whose EXT-X-KEY tag
has a METHOD attribute that it does not recognize.
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If the encryption METHOD is AES-128, AES-128 CBC decryption SHALL be
applied to individual Media Segments, whose encryption format is
described in Section 4.4.4.4.
If the encryption METHOD is AES-128 and the Media Segment is part of
an I-frame Playlist (Section 4.4.3.6) and it has an EXT-X-BYTERANGE
tag applied to it, special care needs to be taken in loading and
decrypting the segment, because the resource identified by the URI is
encrypted in 16-byte blocks from the start of the resource.
The decrypted I-frame can be recovered by first widening its byte
range, as specified by the EXT-X-BYTERANGE tag, so that it starts and
ends on 16-byte boundaries from the start of the resource.
Next, the byte range is widened further to include a 16-byte block at
the beginning of the range. This 16-byte block allows the correct IV
for the following block to be calculated.
The widened byte range can then be loaded and decrypted with AES-128
CBC using an arbitrary IV. The number of bytes added to the
beginning and the end of the original byte range are discarded from
the decrypted bytes; what remains is the decrypted I-frame.
If the encryption METHOD indicates Sample Encryption, decryption
SHALL be applied to encrypted media samples within the Media Segment.
An EXT-X-KEY tag with a METHOD of NONE indicates that the Media
Segments it applies to are not encrypted.
6.3.7. Requesting Playlist Delta Updates
If a Media Playlist file contains an EXT-X-SERVER-CONTROL tag with a
CAN-SKIP-UNTIL attribute and no EXT-X-ENDLIST tag, a Client MAY use
the _HLS_skip Delivery Directive to request Playlist Delta Updates.
A Client SHOULD NOT request a Playlist Delta Update unless it already
has a version of the Playlist that is no older than one-half of the
Skip Boundary.
The client can request a Playlist Delta Update that skips older Media
Segments by adding an "_HLS_skip=YES" directive to the Media Playlist
URI when it requests the Playlist.
Alternately, if the EXT-X-SERVER-CONTROL tag contains a CAN-SKIP-
DATERANGES=YES attribute, the client can request a Playlist Delta
Update that skips both older Segments and older EXT-X-DATERANGE tags
by adding an "_HLS_skip=v2" directive to the Media Playlist URI when
it requests the Playlist.
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A Client MUST merge the contents of a Playlist Delta Update with its
previous version of the Playlist to form an up-to-date version of the
Playlist. If a Client receives a Playlist containing an EXT-X-SKIP
tag and finds that it does not already have all of the information
that was skipped, it MUST obtain a complete copy of the Playlist by
reissuing its Playlist request without the _HLS_skip directive.
6.3.8. Issuing Blocking Requests
Clients MUST NOT request Blocking Playlist Reloads unless the
Playlist contains an EXT-X-SERVER-CONTROL tag with a CAN-BLOCK-
RELOAD=YES attribute.
If Blocking Playlist Reloads are supported, Clients SHOULD use the
_HLS_msn Delivery Directive (and _HLS_part, if the Playlist contains
Partial Segments) to obtain Playlist updates in preference to the
polling regime described in Section 6.3.4.
If up-to-date information on the next expected Media Sequence Number
of a Rendition is not available, a Client SHOULD use a tune-in
algorithm such as the one described in Appendix C to obtain a recent
version of the Playlist.
Clients MUST ignore EXT-X-PRELOAD-HINT tags with unrecognized TYPE
attributes. Clients SHOULD ignore all but the first EXT-X-PRELOAD-
HINT tag in a Playlist with a particular TYPE attribute.
When processing a Playlist containing an EXT-X-PRELOAD-HINT tag with
TYPE=PART, a Client with sufficient space in its download pipeline
that is not already loading the hinted resource SHOULD request it.
This will typically happen at the same time as its blocking request
for the next Playlist update.
When processing a Playlist containing an EXT-X-PRELOAD-HINT tag with
TYPE=MAP, a Client with sufficient space in its download pipeline
that has not already cached the hinted Media Initialization
Section SHOULD request it.
A Client SHOULD cancel a request for a hinted resource if it is not
present in a subsequent Playlist update, such as in an EXT-X-PRELOAD-
HINT tag or as part of another tag such as EXT-X-PART. The client
SHOULD ignore the results of such requests.
A Client SHOULD recognize when a Partial Segment indicated by an EXT-
X-PART tag is a sub-range of a hint download and obtain the Partial
Segment from the hint download. Clients SHOULD recognize contiguous
ranges between existing Partial Segments and Partial Segment hints
and avoid duplicate downloads.
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7. Content Steering
Content Steering allows content providers to group redundant Variant
Streams into "Pathways" and to dynamically prioritize access to
different Pathways. Provision of Pathways by servers is OPTIONAL.
Client support for Content Steering is OPTIONAL. Clients that
support Content Steering MUST follow the rules in this section.
Enabling Content Steering of downloadable (offline) content requires
that each downloadable Rendition have a STABLE-VARIANT-ID or STABLE-
RENDITION-ID, that each Pathway offer Renditions with the same stable
IDs, and that Renditions with the same stable ID have bit-for-bit
identical Media Segments.
7.1. Steering Manifest
Content Steering is accomplished by having clients periodically read
a Steering Manifest from a Steering Server. The Steering Manifest
identifies the available Pathways and their priority order.
The Steering Manifest response is a JSON object:
{
"VERSION": number, // REQUIRED, must be an integer
"TTL": number, // REQUIRED, number of seconds
"RELOAD-URI": string, // OPTIONAL, URI
"PATHWAY-PRIORITY": // REQUIRED, array of Pathway IDs
[
One or more Pathway IDs in order of preference
],
"PATHWAY-CLONES": // OPTIONAL, array of Pathway Clone objects
[
One or more Pathway Clone objects. See Section 7.2.
]
}
A client MUST ignore any key of the Steering Manifest that it does
not recognize. Note that manifest keys are case-sensitive.
This specification defines Steering Manifest VERSION 1. A client
MUST refuse to use a Steering Manifest with an unrecognized VERSION
number.
The TTL specifies how many seconds the client MUST wait before
reloading the Steering Manifest. The recommended value is 300
seconds (5 minutes). The Steering Server MAY vary the TTL by client
to distribute server load.
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The RELOAD-URI, if present, specifies the URI the client MUST use the
next time it obtains the Steering Manifest. The RELOAD-URI MAY be
relative to the current Steering Manifest URI.
PATHWAY-PRIORITY is an array of Pathway IDs. A Pathway ID is a non-
empty string containing characters from the set [a..z], [A..Z],
[0..9], '.', '-', and '_'.
Elements in the PATHWAY-PRIORITY array are ordered by Pathway
preference, with the first being most preferred. A Steering Manifest
MUST contain at least one Pathway. A Pathway ID in the PATHWAY-
PRIORITY array MUST NOT appear more than once. Clients MUST ignore
unrecognized Pathway IDs in the PATHWAY-PRIORITY array.
Note that it is important for the most-preferred Pathway of the
initial Steering Manifest to agree with the Multivariant Playlist.
Immediately redirecting a player to a different Pathway on startup
will delay playback and increase network utilization.
7.2. Pathway Cloning
A steering server can introduce novel Pathways by cloning existing
ones. A Pathway Clone is produced by taking an existing Pathway and
applying well-defined replacements to the Rendition URIs of every
Pathway member.
A Pathway Clone object is a JSON object:
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{
"BASE-ID": string, // REQUIRED. Pathway ID of the Base Pathway
"ID": string, // REQUIRED. Pathway ID for the Pathway Clone
"URI-REPLACEMENT": // REQUIRED. URI replacement rules
{
"HOST": string, // OPTIONAL. Hostname for cloned URIs
"PARAMS": // OPTIONAL. Query parameters for cloned URIs
{
JSON object where keys are query parameter names
and values are query parameter values
},
"PER-VARIANT-URIS": // OPTIONAL. URI overrides per Variant Stream
{
JSON object where keys are STABLE-VARIANT-ID strings
and values are replacement absolute URIs
},
"PER-RENDITION-URIS": // OPTIONAL. URI overrides per Rendition
{
JSON object where keys are STABLE-RENDITION-ID strings
and values are replacement absolute URIs
}
}
}
Clone a Pathway by following these steps:
Identify the Base Pathway, whose ID is the Pathway Clone BASE-ID
string.
Duplicate the Base Pathway. This is functionally equivalent to
(a) duplicating all EXT-X-STREAM-INF and EXT-X-I-FRAME-STREAM-INF
tags whose PATHWAY-ID attributes specify the base PathwayID, (b)
duplicating any EXT-X-MEDIA tags whose GROUP-ID appears as the
AUDIO, VIDEO or SUBTITLE attribute of one of the duplicated EXT-X-
STREAM-INF / EXT-X-I-FRAME-STREAM-INF tags, and (c) giving each
duplicated Rendition Group a new group ID.
Set the ID of the new Pathway to the Pathway Clone ID string. For
every Rendition URI in the new Pathway, resolve it against its
base if necessary and then replace its hostname with the Pathway
Clone HOST string (if present).
Append each name/value pair of the PARAMS object (if present), in
the UTF-8 order of the names, as a query parameter to every
Rendition URI in the new Pathway. If a parameter of the same name
is already present in the Rendition URI, replace it with the one
from the PARAMS object.
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If the STABLE-VARIANT-ID of a Variant Stream on the new Pathway
appears in PER-VARIANT-URIS, set its URI to be the corresponding
value in PER-VARIANT-URIS.
If the STABLE-RENDITION-ID of a Rendition referred to by a Variant
Stream on the new Pathway appears in PER-RENDITION-URIS, set its
URI to be the corresponding value in PER-RENDITION-URIS.
A Pathway Clone MAY use another Pathway Clone as its base if it
appears earlier in the PATHWAY-CLONES array.
The Pathway ID that is defined by a Pathway Clone MAY appear in the
PATHWAY-PRIORITY list, in any position.
The HOST string of a Pathway Clone MUST be non-empty if it is
present.
The name of a PARAMS object name/value pair MUST be non-empty. The
names and values in a PARAMS object MUST be able to form a valid URI
query parameter. Any reserved characters in those strings MUST be
percent-encoded [RFC3986].
A client that does not have the definition of a Pathway specified by
the BASE-ID string of a Pathway Clone object MUST ignore the Pathway
Clone. The client has the definition of a Pathway if it appears in
the original playlist, or appears in the Pathway Clones array from
the current Steering Manifest.
Client support of Pathway Cloning is OPTIONAL. A steering server
SHOULD ensure that the PATHWAY-PRIORITY list always contains at least
one Pathway defined in the Multivariant Playlist.
7.3. Steering Query Parameters
The client sends a request with the Steering Manifest URI to obtain
the Steering Manifest. It SHOULD add the following query parameters
to the URI:
_HLS_pathway="<CURRENT-PATHWAY-ID>"
_HLS_throughput=<THROUGHPUT>
CURRENT-PATHWAY-ID is the ID of the Pathway currently applied by the
client.
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THROUGHPUT is an integer number of bits per second. It represents a
current prediction of media download throughput made by the client
for the applied Pathway. The exact method of bit rate estimation
will vary by client.
HTTP proxy caches SHOULD be configured to exclude highly variable
query parameters such as _HLS_throughput from their cache keys, or
treat the Steering Manifest response as non-cacheable.
7.4. Steering Client Responsibilities
A Pathway is applied by first choosing a particular Pathway ID. The
set of Variant Streams to which the client is allowed to switch is
then restricted to those belonging to that Pathway. If a client is
currently playing a Variant Stream that does not belong to the
applied Pathway, it MUST switch to one that does.
A client that supports Content Steering MUST implement the following
algorithm:
1. When playing a Multivariant Playlist with an EXT-X-CONTENT-
STEERING tag, load the Steering Manifest. A client that wishes
to play before it obtains the Steering Manifest SHOULD apply the
Pathway specified by the PATHWAY-ID of the EXT-X-CONTENT-STEERING
tag. If the EXT-X-CONTENT-STEERING tag does not contain a
PATHWAY-ID attribute, the client MAY use any Pathway until it
obtains the Steering Manifest.
2. When a Steering Manifest is received, perform Pathway Cloning on
any members of the PATHWAY-CLONES array. Then, perform a Content
Steering evaluation (step 5).
3. If all the Variant Streams from the current Pathway fail with a
network error, mark the current Pathway as penalized, and perform
a Content Steering evaluation (step 5).
4. If the client decides that the Pathway has been penalized long
enough that it may have recovered, it SHOULD un-penalize the
Pathway and perform a Content Steering evaluation (step 5).
5. Content Steering evaluation: If no Pathway is currently applied,
or the current Pathway is not the first in the PATHWAY-PRIORITY
list, or is no longer on the list, or is being penalized, then
apply the first non-penalized Pathway on the list. If no such
Pathway is available, the client SHOULD remain on the current
Pathway.
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6. When the current Steering Manifest expires, as defined by the TTL
attribute, issue a new Steering Manifest request for the URI
specified by RELOAD-URI or the previous server URI if none. The
RELOAD-URI may be absolute or relative to the previous server
URI. If the client receives HTTP 410 Gone in response to a
manifest request, it MUST NOT issue another request for that URI
for the remainder of the playback session. It MAY continue to
use the most-recently obtained set of Pathways. If the client
receives HTTP 429 Too Many Requests with a Retry-After header in
response to a manifest request, it SHOULD wait until the time
specified by the Retry-After header to reissue the request.
7. If the Steering Manifest cannot be loaded and parsed correctly,
the client SHOULD continue to use the previous values and attempt
to reload it after waiting for the previously-specified TTL (or 5
minutes if none).
8. Protocol Version Compatibility
Protocol compatibility is specified by the EXT-X-VERSION tag. A
Playlist that contains tags or attributes that are not compatible
with protocol version 1 MUST include an EXT-X-VERSION tag.
A client MUST NOT attempt playback if it does not support the
protocol version specified by the EXT-X-VERSION tag, or unintended
behavior could occur.
A Media Playlist MUST indicate an EXT-X-VERSION of 2 or higher if it
contains:
* The IV attribute of the EXT-X-KEY tag.
A Media Playlist MUST indicate an EXT-X-VERSION of 3 or higher if it
contains:
* Floating-point EXTINF duration values.
A Media Playlist MUST indicate an EXT-X-VERSION of 4 or higher if it
contains:
* The EXT-X-BYTERANGE tag.
* The EXT-X-I-FRAMES-ONLY tag.
A Media Playlist MUST indicate an EXT-X-VERSION of 5 or higher if it
contains:
* An EXT-X-KEY tag with a METHOD of SAMPLE-AES.
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* The KEYFORMAT and KEYFORMATVERSIONS attributes of the EXT-X-KEY
tag.
* The EXT-X-MAP tag.
A Media Playlist MUST indicate an EXT-X-VERSION of 6 or higher if it
contains:
* The EXT-X-MAP tag in a Media Playlist that does not contain EXT-
X-I-FRAMES-ONLY.
Note that in protocol version 6, the semantics of the EXT-
X-TARGETDURATION tag changed slightly. In protocol version 5 and
earlier it indicated the maximum segment duration; in protocol
version 6 and later it indicates the maximum segment duration rounded
to the nearest integer number of seconds.
A Multivariant Playlist MUST indicate an EXT-X-VERSION of 7 or higher
if it contains:
* "SERVICE" values for the INSTREAM-ID attribute of the EXT-X-MEDIA
tag.
A Playlist MUST indicate an EXT-X-VERSION of 8 or higher if it
contains:
* Variable substitution.
A Playlist MUST indicate an EXT-X-VERSION of 9 or higher if it
contains:
* The EXT-X-SKIP tag.
A Playlist MUST indicate an EXT-X-VERSION of 10 or higher if it
contains:
* An EXT-X-SKIP tag that replaces EXT-X-DATERANGE tags in a Playlist
Delta Update.
The EXT-X-MEDIA tag and the AUDIO, VIDEO, and SUBTITLES attributes of
the EXT-X-STREAM-INF tag are backward compatible to protocol version
1, but playback on older clients may not be desirable. A server MAY
consider indicating an EXT-X-VERSION of 4 or higher in the
Multivariant Playlist but is not required to do so.
The PROGRAM-ID attribute of the EXT-X-STREAM-INF and the EXT-X-I-
FRAME-STREAM-INF tags was removed in protocol version 6.
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The EXT-X-ALLOW-CACHE tag was removed in protocol version 7.
9. Playlist Examples
In some examples a '\' is used to indicate that the tag continues on
the following line with whitespace removed.
9.1. Simple Media Playlist
#EXTM3U
#EXT-X-TARGETDURATION:10
#EXT-X-VERSION:3
#EXTINF:9.009,
http://media.example.com/first.ts
#EXTINF:9.009,
http://media.example.com/second.ts
#EXTINF:3.003,
http://media.example.com/third.ts
#EXT-X-ENDLIST
9.2. Live Media Playlist Using HTTPS
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:8
#EXT-X-MEDIA-SEQUENCE:2680
#EXTINF:7.975,
https://priv.example.com/fileSequence2680.ts
#EXTINF:7.941,
https://priv.example.com/fileSequence2681.ts
#EXTINF:7.975,
https://priv.example.com/fileSequence2682.ts
9.3. Playlist with Encrypted Media Segments
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#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:7794
#EXT-X-TARGETDURATION:15
#EXT-X-KEY:METHOD=AES-128,URI="https://priv.example.com/key.php?r=52"
#EXTINF:2.833,
http://media.example.com/fileSequence52-A.ts
#EXTINF:15.0,
http://media.example.com/fileSequence52-B.ts
#EXTINF:13.333,
http://media.example.com/fileSequence52-C.ts
#EXT-X-KEY:METHOD=AES-128,URI="https://priv.example.com/key.php?r=53"
#EXTINF:15.0,
http://media.example.com/fileSequence53-A.ts
9.4. Multivariant Playlist
#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1280000,AVERAGE-BANDWIDTH=1000000
http://example.com/low.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2560000,AVERAGE-BANDWIDTH=2000000
http://example.com/mid.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=7680000,AVERAGE-BANDWIDTH=6000000
http://example.com/hi.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
http://example.com/audio-only.m3u8
9.5. Multivariant Playlist with I-Frames
#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1280000
low/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=86000,URI="low/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2560000
mid/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=150000,URI="mid/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=7680000
hi/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=550000,URI="hi/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
audio-only.m3u8
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9.6. Multivariant Playlist with Alternative Audio
In this example, the CODECS attributes have been condensed for space.
#EXTM3U
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="English", \
DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="en", \
URI="main/english-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Deutsch", \
DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="de", \
URI="main/german-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Commentary", \
DEFAULT=NO,AUTOSELECT=NO,LANGUAGE="en", \
URI="commentary/audio-only.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",AUDIO="aac"
low/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",AUDIO="aac"
mid/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",AUDIO="aac"
hi/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5",AUDIO="aac"
main/english-audio.m3u8
9.7. Multivariant Playlist with Alternative Video
This example shows three different video Renditions (Main,
Centerfield, and Dugout) and three different Variant Streams (low,
mid, and high). In this example, clients that did not support the
EXT-X-MEDIA tag and the VIDEO attribute of the EXT-X-STREAM-INF tag
would only be able to play the video Rendition "Main".
Since the EXT-X-STREAM-INF tag has no AUDIO attribute, all video
Renditions would be required to contain the audio.
In this example, the CODECS attributes have been condensed for space.
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#EXTM3U
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Main", \
DEFAULT=YES,URI="low/main/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Centerfield", \
DEFAULT=NO,URI="low/centerfield/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Dugout", \
DEFAULT=NO,URI="low/dugout/audio-video.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",VIDEO="low"
low/main/audio-video.m3u8
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Main", \
DEFAULT=YES,URI="mid/main/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Centerfield", \
DEFAULT=NO,URI="mid/centerfield/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Dugout", \
DEFAULT=NO,URI="mid/dugout/audio-video.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",VIDEO="mid"
mid/main/audio-video.m3u8
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Main", \
DEFAULT=YES,URI="hi/main/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Centerfield", \
DEFAULT=NO,URI="hi/centerfield/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Dugout", \
DEFAULT=NO,URI="hi/dugout/audio-video.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",VIDEO="hi"
hi/main/audio-video.m3u8
9.8. Session Data in a Multivariant Playlist
In this example, only the EXT-X-SESSION-DATA is shown:
#EXT-X-SESSION-DATA:DATA-ID="com.example.lyrics",URI="lyrics.json"
#EXT-X-SESSION-DATA:DATA-ID="com.example.title",LANGUAGE="en", \
VALUE="This is an example"
#EXT-X-SESSION-DATA:DATA-ID="com.example.title",LANGUAGE="es", \
VALUE="Este es un ejemplo"
9.9. CHARACTERISTICS Attribute Containing Multiple Characteristics
Certain characteristics are valid in combination, as in:
CHARACTERISTICS=
"public.accessibility.transcribes-spoken-dialog,public.easy-to-read"
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9.10. EXT-X-DATERANGE Carrying SCTE-35 Tags
This example shows two EXT-X-DATERANGE tags that describe a single
Date Range, with an SCTE-35 "out" splice_insert() command that is
subsequently updated with an SCTE-35 "in" splice_insert() command.
#EXTM3U
...
#EXT-X-DATERANGE:ID="splice-6FFFFFF0", \
START-DATE="2014-03-05T11:15:00Z",PLANNED-DURATION=59.993, \
SCTE35-OUT=0xFC002F0000000000FF000014056FFFFFF000E011622DCAFF0 \
00052636200000000000A0008029896F50000008700000000
... Media Segment declarations for 60s worth of media
#EXT-X-DATERANGE:ID="splice-6FFFFFF0",DURATION=59.993, \
SCTE35-IN=0xFC002A0000000000FF00000F056FFFFFF000401162802E610 \
0000000000A0008029896F50000008700000000
...
9.11. Low-Latency Playlist
This example shows the end of a Playlist that contains Partial
Segments. Note that EXT-X-PART tags have been removed from earlier
Parent Segments. The Playlist also includes a Preload Hint, a
Rendition Report, and a mid-roll advertisement.
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#EXTM3U
#EXT-X-TARGETDURATION:4
...
#EXTINF:4.00008,
fileSequence268.mp4
#EXTINF:4.00008,
fileSequence269.mp4
#EXTINF:4.00008,
fileSequence270.mp4
#EXT-X-PART:DURATION=2.00004,INDEPENDENT=YES,URI="filePart271.0.mp4"
#EXT-X-PART:DURATION=2.00004,URI="filePart271.1.mp4"
#EXTINF:4.00008,
fileSequence271.mp4
#EXT-X-PART:DURATION=2.00004,INDEPENDENT=YES,URI="filePart272.0.mp4"
#EXT-X-PART:DURATION=0.50001,URI="filePart272.1.mp4"
#EXTINF:2.50005,
fileSequence272.mp4
#EXT-X-DISCONTINUITY
#EXT-X-PART:DURATION=2.00004,INDEPENDENT=YES,URI="midRoll273.0.mp4"
#EXT-X-PART:DURATION=2.00004,URI="midRoll273.1.mp4"
#EXTINF:4.00008,
midRoll273.mp4
#EXT-X-PART:DURATION=2.00004,INDEPENDENT=YES,URI="midRoll274.0.mp4"
#EXT-X-PRELOAD-HINT:TYPE=PART,URI="midRoll274.1.mp4"
#EXT-X-RENDITION-REPORT:URI="/1M/LL-HLS.m3u8",LAST-MSN=274,LAST-PART=1
9.12. Content Steering Playlist and Manifest
This example shows a Multivariant Playlist and a corresponding
Steering Manifest. The Multivariant Playlist URI is
https://example.com/videos/video12/mv.m3u8. Line breaks have been
added for legibility.
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#EXTM3U
#EXT-X-CONTENT-STEERING:SERVER-URI="/steering?video=00012", \
PATHWAY-ID="CDN-A"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="A",NAME="English",DEFAULT=YES, \
URI="eng.m3u8",LANGUAGE="en",STABLE-RENDITION-ID="Audio-37262"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="B",NAME="ENGLISH",DEFAULT=YES, \
URI="https://b.example.com/content/videos/video12/eng.m3u8", \
LANGUAGE="en",STABLE-RENDITION-ID="Audio-37262"
#EXT-X-STREAM-INF:BANDWIDTH=1280000,AUDIO="A",PATHWAY-ID="CDN-A", \
STABLE-VARIANT-ID="Video-128"
low/video.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=7680000,AUDIO="A",PATHWAY-ID="CDN-A", \
STABLE-VARIANT-ID="Video-768"
hi/video.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1280000,AUDIO="B",PATHWAY-ID="CDN-B", \
STABLE-VARIANT-ID="Video-128"
https://backup.example.com/content/videos/video12/low/video.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=7680000,AUDIO="B",PATHWAY-ID="CDN-B", \
STABLE-VARIANT-ID="Video-768"
https://backup.example.com/content/videos/video12/hi/video.m3u8
{
"VERSION": 1,
"TTL": 300,
"RELOAD-URI": "https://example.com/steering?video=00012&session=123",
"PATHWAY-PRIORITY": [
"CDN-A",
"CDN-B"
]
}
9.13. Content Steering Manifest with Pathway Clone
This example extends the previous example with a Steering Manifest
that includes a Pathway Clone.
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{
"VERSION": 1,
"TTL": 300,
"PATHWAY-PRIORITY": [
"CDN-A-CLONE",
"CDN-A"
],
"PATHWAY-CLONES": [
{
"BASE-ID": "CDN-A",
"ID": "CDN-A-CLONE",
"URI-REPLACEMENT":
{
"HOST": "backup2.example.com",
"PARAMS":
{
"token": "dkfs1239414"
}
"PER-RENDITION-URIS": {
"Audio-37262": "https://q.example.com/video12/eng.m3u8"
}
}
}
]
}
The Pathway Clone with ID "CDN-A-CLONE" will have the URIs:
https://backup2.example.com/videos/video12/low/video.m3u8?token=dkfs1239414
https://backup2.example.com/videos/video12/hi/video.m3u8?token=dkfs1239414
https://q.example.com/video12/eng.m3u8
10. Contributors
Significant contributions to the design of this protocol were made by
Jim Batson, David Biderman, Bill May, Roger Pantos, Alan Tseng, and
Eryk Vershen. Stuart Cheshire helped edit the specification.
Significant contributions to the update of this protocol were made by
Bill May, Eryk Vershen, and Peng Zhou.
In particular, Bill May co-authored the first edition of HTTP Live
Streaming, [RFC8216], and continues to provide valuable guidance and
input.
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11. IANA Considerations
11.1. vnd.apple.mpegurl
IANA has registered the following media type [RFC2046]:
Type name: application
Subtype name: vnd.apple.mpegurl
Required parameters: none
Optional parameters: none
Encoding considerations: encoded as UTF-8, which is 8-bit text. This
media type may require encoding on transports not capable of handling
8-bit text. See Section 4 for more information.
Security considerations: See Section 12.
Compression: this media type does not employ compression.
Interoperability considerations: There are no byte-ordering issues
since files are 8-bit text. Applications could encounter
unrecognized tags, which SHOULD be ignored.
Published specification: see Section 4.
Applications that use this media type: Multimedia applications such
as the iPhone media player in iOS 3.0 and later and QuickTime Player
in Mac OS X version 10.6 and later.
Fragment identifier considerations: no Fragment Identifiers are
defined for this media type.
Query parameter considerations: the definition of all query
parameters for resources of this media type which begin with the
string "_HLS_" are reserved by this specification. Currently-defined
query parameters are specified in Section 6.2.5 and Appendix D.3.
Additional information:
Deprecated alias names for this type: none
Magic number(s): #EXTM3U
File extension(s): .m3u8, .m3u (see Section 4)
Macintosh file type code(s): none
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Person & email address to contact for further information: David
Singer, singer AT apple.com.
Intended usage: LIMITED USE
Restrictions on usage: none
Author: Roger Pantos
Change Controller: David Singer
11.2. vnd.apple.steering-list
IANA has registered the following media type [RFC2046]:
Type name: application
Subtype name: vnd.apple.steering-list
Required parameters: none
Optional parameters: none
Encoding considerations: encoded as JSON (UTF-8), which is 8-bit
text. This media type may require encoding on transports not capable
of handling 8-bit text. See Section 7.1 for more information.
Security considerations: See Section 12.
Compression: this media type does not employ compression.
Interoperability considerations: There are no byte-ordering issues
since files are 8-bit text. Applications could encounter
unrecognized keys, which SHOULD be ignored.
Published specification: see Section 7.1.
Applications that use this media type: Multimedia applications such
as the iPhone media player in iOS 15.0 and later and QuickTime Player
in macOS Monterey and later.
Fragment identifier considerations: no Fragment Identifiers are
defined for this media type.
Query parameter considerations: the definition of all query
parameters for resources of this media type which begin with the
string "_HLS_" are reserved by this specification. Currently-defined
query parameters are specified in Section 7.3.
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Additional information:
Deprecated alias names for this type: none
Magic number(s): none
File extension(s): .json (see Section 7.1)
Macintosh file type code(s): none
Person & email address to contact for further information: David
Singer, singer AT apple.com.
Intended usage: LIMITED USE
Restrictions on usage: none
Author: Roger Pantos
Change Controller: David Singer
12. Security Considerations
Since the protocol generally uses HTTP to transfer data, most of the
same security considerations apply. See Section 15 of HTTP
[RFC7230].
Media file parsers are typically subject to "fuzzing" attacks.
Implementors SHOULD pay particular attention to code that will parse
data received from a server and ensure that all possible inputs are
handled correctly.
Playlist files contain URIs, which clients will use to make network
requests of arbitrary entities. Clients SHOULD range-check responses
to prevent buffer overflows. See also the Security Considerations
section of "Uniform Resource Identifier (URI): Generic Syntax"
[RFC3986].
Apart from URI resolution, this format does not employ any form of
active content.
Clients SHOULD limit each playback session to a reasonable number of
concurrent downloads (for example, four) to avoid contributing to
denial-of-service attacks.
HTTP requests often include session state ("cookies"), which may
contain private user data. Implementations MUST follow cookie
restriction and expiry rules specified by "HTTP State Management
Mechanism" [RFC6265] to protect themselves from attack. See also the
Security Considerations section of that document, and "Use of HTTP
State Management" [RFC2964].
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Encryption keys are specified by URI. The delivery of these keys
SHOULD be secured by a mechanism such as HTTP Over TLS [RFC2818]
(formerly SSL) in conjunction with a secure realm or a session token.
13. References
13.1. Normative References
[AC_3] Advanced Television Systems Committee, "Digital Audio
Compression (AC-3) (E-AC-3)", ATSC Standard A/52:2010, 22
November 2010, <http://atsc.org/wp-
content/uploads/2015/03/A52-201212-17.pdf>.
[AES_128] National Institute of Standards and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, DOI
10.6028/NIST.FIPS.197, November 2001,
<http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf>.
[CEA608] Consumer Technology Association, "Line 21 Data Services",
ANSI/CTA Standard 608-E, April 2008,
<https://standards.cta.tech/kwspub/published_docs/ANSI-
CTA-608-E-R-2014-Preview.pdf>.
[CEA708] Consumer Technology Association, "Digital Television (DTV)
Closed Captioning", ANSI/CTA Standard CEA-708-E, August
2013, <https://standards.cta.tech/kwspub/published_docs/
ANSI-CTA-708-E-Preview.pdf>.
[CICP] International Organization for Standardization,
"Information technology - MPEG systems technologies - Part
8: Coding-independent code points", ISO/IEC International
Standard 23001-8:2016, 2016, <https://www.iso.org/obp/
ui/#iso:std:iso-iec:23001:-8:ed-2:v1:en>.
[CMAF] International Organization for Standardization,
"Information technology -- Multimedia application format
(MPEG-A) -- Part 19: Common media application format
(CMAF) for segmented media", ISO/IEC International
Standard 23000-19:2017, December 2017,
<https://www.iso.org/standard/71975.html>.
[COMMON_ENC]
International Organization for Standardization,
"Information technology -- MPEG systems technologies --
Part 7: Common encryption in ISO base media file format
files", ISO/IEC International Standard 23001-7:2016,
February 2016, <http://www.iso.org/iso/
catalogue_detail.htm?csnumber=68042>.
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[HDCP] Digital Content Protection LLC, "High-bandwidth Digital
Content Protection System - Mapping HDCP to HDMI",
February 2013, <http://www.digital-
cp.com/sites/default/files/specifications/
HDCP%20on%20HDMI%20Specification%20Rev2_2_Final1.pdf>.
[H_264] International Telecommunications Union, "Advanced video
coding for generic audiovisual services", January 2012,
<http://www.itu.int/rec/T-REC-H.264>.
[IMSC1] W3C, "TTML Profiles for Internet Media Subtitles and
Captions 1.0 (IMSC1)", April 2016,
<https://www.w3.org/TR/ttml-imsc1/>.
[ISOBMFF] International Organization for Standardization,
"Information technology -- Coding of audio-visual objects
-- Part 12: ISO base media file format", ISO/IEC
International Standard 14496-12:2015, December 2015,
<http://www.iso.org/iso/
catalogue_detail.htm?csnumber=68960>.
[ISO_13818]
International Organization for Standardization, "Generic
coding of moving pictures and associated audio
information", ISO/IEC International Standard 13818:2007,
October 2007,
<http://www.iso.org/iso/catalogue_detail?csnumber=44169>.
[ISO_13818_3]
International Organization for Standardization, "Generic
coding of moving pictures and associated audio information
-- Part 3: Audio", ISO/IEC International
Standard 13818-3:1998, April 1998,
<http://www.iso.org/iso/home/store/catalogue_tc/
catalogue_detail.htm?csnumber=26797>.
[ISO_13818_7]
International Organization for Standardization, "Generic
coding of moving pictures and associated audio information
-- Part 7: Advanced Audio Coding (AAC)", ISO/IEC
International Standard 13818-7:2006, January 2006,
<http://www.iso.org/iso/home/store/catalogue_tc/
catalogue_detail.htm?csnumber=43345>.
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[ISO_14496]
International Organization for Standardization,
"Information technology -- Coding of audio-visual objects
-- Part 3: Audio", ISO/IEC International
Standard 14496-3:2009, 2009,
<http://www.iso.org/iso/catalogue_detail?csnumber=53943>.
[ISO_8601] International Organization for Standardization, "Data
elements and interchange formats -- Information
interchange -- Representation of dates and times", ISO/IEC
International Standard 8601:2004, December 2004,
<http://www.iso.org/iso/catalogue_detail?csnumber=40874>.
[MP4_TIMED_TEXT]
International Organization for Standardization,
"Information technology -- Coding of audio-visual objects
-- Part 30: Timed text and other visual overlays in ISO
base media file format", ISO/IEC International
Standard 14496-30:2014, March 2014,
<https://www.iso.org/standard/63107.html>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC2964] Moore, K. and N. Freed, "Use of HTTP State Management",
BCP 44, RFC 2964, DOI 10.17487/RFC2964, October 2000,
<https://www.rfc-editor.org/info/rfc2964>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
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[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.
[RFC6381] Gellens, R., Singer, D., and P. Frojdh, "The 'Codecs' and
'Profiles' Parameters for "Bucket" Media Types", RFC 6381,
DOI 10.17487/RFC6381, August 2011,
<https://www.rfc-editor.org/info/rfc6381>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8216] Pantos, R., Ed. and W. May, "HTTP Live Streaming",
RFC 8216, DOI 10.17487/RFC8216, August 2017,
<https://www.rfc-editor.org/info/rfc8216>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8673] Pratt, C., Thakore, D., and B. Stark, "HTTP Random Access
and Live Content", RFC 8673, DOI 10.17487/RFC8673,
November 2019, <https://www.rfc-editor.org/info/rfc8673>.
[SCTE35] Society of Cable Telecommunications Engineers, "Digital
Program Insertion Cueing Message for Cable", ANSI/SCTE 35,
August 2014, <http://www.scte.org/documents/pdf/Standards/
ANSI_SCTE%2035%202014.pdf>.
[US_ASCII] American National Standards Institute, "Coded Character
Sets - 7-Bit American National Standard Code for
Information Interchange (7-Bit ASCII)", ANSI X3.4, 30
December 1986.
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[WebVTT] World Wide Web Consortium (W3C), ""WebVTT: The Web Video
Text Tracks Format", Draft Community Group Report", July
2013, <http://dev.w3.org/html5/webvtt/>.
13.2. Informative References
[ID3] ID3.org, "The ID3 audio file data tagging format",
<https://id3.org/Developer%20Information>.
[M3U] "M3U (MP3 URL)", <http://wikipedia.org/wiki/M3U>.
[MCT] Apple Inc., "QuickTime File Format Specification - Media
Characteristic Tags", <https://developer.apple.com/library
/archive/documentation/QuickTime/QTFF/QTFFChap2/
qtff2.html>.
[MP4RA] International Organization for Standardization, "Official
Registration Authority for the ISOBMFF family of
standards", <https://mp4ra.org>.
[SampleEnc]
Apple Inc., "MPEG-2 Stream Encryption Format for HTTP Live
Streaming",
<https://developer.apple.com/library/ios/documentation/
AudioVideo/Conceptual/HLS_Sample_Encryption/>.
[UNICODE] The Unicode Consortium, "The Unicode Standard",
<https://www.unicode.org/versions/latest/>.
Appendix A. Changes from RFC 8216
Several changes have been made since the publication of RFC 8216
[RFC8216].
A "Multivariant Playlist" was formerly called a "Master Playlist".
The following tags have been added: EXT-X-GAP, EXT-X-BITRATE, EXT-X-
SERVER-CONTROL, EXT-X-SKIP, EXT-X-PART-INF, EXT-X-PART, EXT-X-
PRELOAD-HINT, EXT-X-RENDITION-REPORT, and EXT-X-CONTENT-STEERING.
The EXT-X-DEFINE tag was introduced to support variable substitution.
IMSC has been added to the set of recognized subtitle formats.
The VIDEO-RANGE, ALLOWED-CPC, STABLE-VARIANT-ID, PATHWAY-ID, and
SUPPLEMENTAL-CODECS attributes have been added to the EXT-X-STREAM-
INF and EXT-X-I-FRAME-STREAM-INF tags.
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The STABLE-RENDITION-ID attribute has been added to the EXT-X-MEDIA
tag.
The CUE attribute has been added to the EXT-X-DATERANGE tag.
TYPE-1 has been added as a defined value for the HDCP-LEVEL
attribute.
Redefined the CHANNELS attribute value.
The minimum new segment publication latency has been removed from
server timing model.
The Availability Duration of a Media Segment now depends on the
presence of an EXT-X-ENDLIST tag.
The recommended playlist offset to join a live stream has changed.
The minimum delay before reloading a Playlist file has changed.
The definition of peak segment bit rate was changed to ensure every
segment is included in at least one contiguous set.
Media Metadata tags such as EXT-X-DATERANGE may be removed from
playlists.
Partial Segments were defined as a means to reduce publishing
latency. Earlier versions of this specification had different rules
for the minimum allowable Partial Segment duration for streams that
contain gaps.
Delivery Directives were introduced, including support for Playlist
Delta Updates and Blocking Playlist Reload.
A Low-Latency Server Configuration Profile was added to Appendix B.
Correct the reference for the semantics of the CHARACTERISTICS
attribute.
Appendix C was added.
Content Steering (Section 7) was defined to allow alternate Pathways
to the presentation, including Pathway Cloning.
The IANA media type vnd.apple.steering-list (Section 11.2) was added.
Interstitials (Appendix D) were defined to simplify inserting bumpers
or advertising content.
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The type enumerated-string-list was added to the possible
AttributeValues.
Clarified the expected availability of Partial Segments.
There have been a number of minor editorial changes.
Appendix B. Server Configuration Profiles
Server Configuration Profiles specify additional requirements that
optimize delivery of HTTP Live Streaming for certain use cases.
B.1. Low-Latency Server Configuration Profile
Playing at a reduced delay from live requires certain stream and
transport features to support the timely delivery of media. Clients
SHOULD verify that the server meets these requirements before playing
at a delay-from-live of less than two Target Durations. Because the
Low-Latency extensions are additions rather than replacements,
clients can and SHOULD fall back to regular-latency playback if they
discover that the server does not meet the requirements of this
configuration profile.
This profile places the following requirements on stream production:
All Media Playlists have EXT-X-PROGRAM-DATE-TIME tags. This
allows more-precise mapping between Segments across Renditions.
Note that real-time clocks are NOT required to be synchronized
between client and server.
Each (non-Partial) Media Segment in a Media Playlist will contain
at least one independent frame.
A Playlist that contains an EXT-X-PART tag but no EXT-X-ENDLIST
tag will also contain an EXT-X-PRELOAD-HINT tag that specifies the
next Partial Segment that is expected to be added to the Playlist.
If the Partial Segment specified by an EXT-X-PRELOAD-HINT tag has
a different Media Initialization Section than the last Partial
Segment in the Playlist, the Playlist will also contain an EXT-X-
PRELOAD-HINT tag with TYPE=MAP that hints the Media Initialization
Section of the hinted Partial Segment.
Each Media Playlist contains one EXT-X-RENDITION-REPORT tag for
each Media Playlist (Rendition) in the Multivariant Playlist,
except for the Media Playlist to which the EXT-X-RENDITION-REPORT
tag is being added, and Playlists that contain the EXT-X-I-FRAMES-
ONLY tag.
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This profile places the following requirements on stream delivery:
HTTP-delivered Playlists and Segments are served via HTTP/2.
Efficient delivery requires HTTP/2 priority control (dependencies
and weights) and support for Ping frames.
Each server offers the entire set of Variant Streams in the
Multivariant Playlist. This allows rapid bit rate switching
without connection reestablishment.
Servers support HTTP Range requests if Media Playlists contain the
BYTERANGE, BYTERANGE-START, or BYTERANGE-LENGTH attributes.
TCP connections support Selective Acknowledgment (SACK) across the
entire route from client to server. This improves the performance
of TCP loss recovery
Playlist requests are idempotent.
Playlists are delivered in GZIP format. This speeds up Media
Playlist reload and Rendition switching.
All Renditions in a Multivariant Playlist are updated in sync,
within an accuracy of one Part Target Duration.
CDNs and other proxy caches recognize blocking requests for
Playlists and Media Segments whose cache fill is already pending,
and hold the duplicate requests until they can be delivered from
that cache fill. This minimizes the load on the active origin.
HTTP caches used to deliver Playlists or Segments will set the Age
HTTP Response header.
In addition, the following configurations are recommended:
TCP connections should set Explicit Congestion Notification (ECN)
during congestion. They should also use TCP timestamps, TAIL LOSS
probe, and TCP RACK. These configurations improve the performance
of TCP loss recovery. See RFC 2018, RFC 3168, RFC 7323, and IETF
draft-ietf-tcpm-rack for more information about these TCP options.
Servers should support TLS 1.3 or higher. This reduces time to
connect. Servers should also support TLS 1.3 0-RTT connections
for Media Playlists and Media Segments.
Blocking Playlist Reload allows longer caching of Playlists
without detriment to Clients. Successful responses to blocking
Playlist requests should be cached for six Target Durations.
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Unsuccessful responses (such as 404s) should be cached for four
Target Durations. Successful responses to non-blocking Playlist
requests should be cached for half the Target Duration.
Unsuccessful responses to non-blocking Playlist requests should be
cached for for one Target Duration.
Successful responses to blocking Media segment requests should be
cached for six Target Durations. Unsuccessful responses should be
cached for one Target Duration.
Origin servers should use Cache-Control headers to communicate the
desired cache lifetime.
The recommended Target Duration is six seconds.
The recommended GOP size is between one and two seconds. Smaller
GOPs allow faster switching between Renditions.
Appendix C. Low-Latency CDN Tune-in
Clients SHOULD support delivery of low-latency streams through CDNs
and other HTTP caches. Correctly implementing PART-HOLD-BACK, the
server-recommended playback delay from live, requires that the client
first obtain a reasonably up-to-date version of the Media Playlist.
There are various approaches that a client may take to obtain a
recent version of a Media Playlist. The following algorithm
typically requires two Playlist requests to obtain a Playlist that is
within one Part Target Duration of the current Playlist:
1. Send a request for the Media Playlist that does not include an
_HLS_msn or _HLS_part directive.
2. Record the first Playlist response, including its received time
and Age header. If there's no Age header in the first Playlist
response, consider the Playlist to be up to date. (No Age header
means that the response came directly from the origin, rather
than being held for a period of time in an intervening HTTP
cache.)
3. If there is an Age header in the first Playlist response, set the
goalDuration to match the Age value. Increase the goalDuration
by one second if the Part Target Duration is less than 1.0.
4. While the Age value is greater than or equal to the floor of the
Part Target Duration:
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A. Set currentGoal to be the goalDuration plus the amount of
time since the first Playlist response.
B. If the current version of the Playlist has at least
currentGoal more media in it than the first Playlist,
consider the current Playlist to be up to date.
C. Use the Target Duration and the Part Target Duration to
estimate how many more segments and parts the server will add
to the Playlist to contribute at least currentGoal more media
to it.
D. Request the Media Playlist again, using the _HLS_msn and
_HLS_part directives to obtain the Playlist that has the
estimated additional duration of media since the first
Playlist.
E. Update the current Playlist and the Age value from the
Playlist response.
Appendix D. Interstitials
Content vendors can insert separate interstitial content into their
primary presentations in order to display advertising, branding, or
other information to viewers.
D.1. Overview
Servers can schedule interstitials by placing EXT-X-DATERANGE tags
into the Media Playlists of the primary asset.
Interstitials themselves are self-contained media assets. They can
be scheduled anywhere on the timeline of a primary media asset.
While interstitials MUST be VOD assets, they can be scheduled against
either VOD or live primary content (including Low-Latency HLS streams
(Appendix B.1)).
Interstitials are specified by URI. The client SHOULD load the
resource specified by the URI after it buffers the primary asset to
the scheduled interstitial playback time. This allows for late
binding to interstitial content. Since an interstitial is described
by a single URI, a server can respond to it with a limited number of
HTTP redirects without a major impact on performance.
An interstitial request can either be for a single interstitial asset
or a list of assets. In the second case, the composition of the list
MAY be determined when the server responds to the interstitial
request.
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Each interstitial asset is a Playlist, usually a Multivariant
Playlist. The primary media asset and the interstitial asset both
provide sets of Variant Streams. The two sets MAY have different
characteristics. The bit rates of the Variant Streams of the
interstital asset may not exactly match those of the primary asset,
but they SHOULD allow for effective bit rate adaptation in similar
network conditions. It is RECOMMENDED that the set of languages in
Rendition Groups of a specific type within the interstitial asset
match those used in the primary media asset. Interstitials MAY use
the different codecs from the primary content, although using
different codecs will cause transition delays on certain devices.
Devices that do not implement HLS interstitial support SHOULD ignore
server-generated interstitial events when playing a primary asset.
Interstitials scheduled inside other interstitials MUST be ignored by
clients.
D.2. EXT-X-DATERANGE Schema for Interstitials
The server MAY insert EXT-X-DATERANGE tags according to the rules in
this section to tell the client to schedule interstitial playback.
An Interstitial EXT-X-DATERANGE tag MUST have a CLASS attribute whose
value is "com.apple.hls.interstitial". This class defines the
following attributes:
X-ASSET-URI
The value of the X-ASSET-URI is a quoted-string absolute URI for a
single interstitial asset. An Interstitial EXT-X-DATERANGE tag
MUST have either the X-ASSET-URI attribute or the X-ASSET-LIST
attribute. It MUST NOT have both.
X-ASSET-LIST
The value of the X-ASSET-LIST is a quoted-string URI to a JSON
object.
The JSON object MUST contain a key/value pair whose key is
"ASSETS" and whose value is a JSON array of Asset-Description JSON
objects. (Note that keys in a JSON object are case-sensitive.)
Each Asset-Description JSON object MUST have a "URI" member whose
value is a quoted-string absolute URI for a single interstitial
asset, and a "DURATION" member whose value is a decimal-floating-
point indicating the duration of the interstitial asset in
seconds.
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The client SHOULD play the interstitial assets back-to-back in the
order that they appear in the ASSETS array.
X-RESUME-OFFSET
The value of X-RESUME-OFFSET is a decimal-floating-point of
seconds that specifies where primary playback is to resume
following the playback of the interstitial. It is expressed as a
time offset from where the interstitial playback was scheduled on
the primary player timeline. A typical value for X-RESUME-OFFSET
is zero. This attribute is OPTIONAL.
If the X-RESUME-OFFSET is not present, its value is considered to
be the duration of the interstitial. This is appropriate for live
content, where playback is to be kept at a constant delay from the
live edge, or for VOD playback where the HLS interstitial is
intended to exactly replace content in the primary asset.
X-PLAYOUT-LIMIT
The value of X-PLAYOUT-LIMIT is a decimal-floating-point of
seconds that specifies a limit for the playout time of the entire
interstitial. If it is present, the client SHOULD end the
interstitial if playback reaches that offset from its start.
Otherwise the interstitial MUST end upon reaching the end of the
interstitial asset(s). This attribute is OPTIONAL.
X-SNAP
The value of the X-SNAP attribute is an enumerated-string-list of
Snap Identifiers. The defined Snap Identifiers are: OUT and IN.
This attribute is OPTIONAL.
If the list contains OUT then the client SHOULD locate the segment
boundary closest to the START-DATE of the interstitial in the
Media Playlist of the primary content and transition to the
interstitial at that boundary. If more than one Media Playlist is
contributing to playback (audio plus video for example), the
client SHOULD transition at the earliest segment boundary.
If the list contains IN then the client SHOULD locate the segment
boundary closest to the scheduled resumption point from the
interstitial in the Media Playlist of the primary content and
resume playback of primary content at that boundary. If more than
one Media Playlist is contributing to playback, the client SHOULD
transition at the latest segment boundary.
X-RESTRICT
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The value of the X-RESTRICT attribute is an enumerated-string-list
of Navigation Restriction Identifiers. The defined Navigation
Restriction Identifiers are: SKIP and JUMP. These restrictions
are enforced at the player UI level. This attribute is OPTIONAL.
If the list contains SKIP then while the interstitial is being
played, the client MUST NOT allow the user to seek forward from
the current playhead position or set the rate to greater than the
regular playback rate until playback reaches the end of the
interstitial.
If the list contains JUMP then the client MUST NOT allow the user
to seek from a position in the primary asset earlier than the
START-DATE attribute to a position after it without first playing
the interstitial asset, even if the interstitial at START-DATE was
played through earlier. If the user attempts to seek across more
than one interstitial, the client SHOULD choose at least one
interstitial to play before allowing the seek to complete.
X-<client-attribute>
Client-defined attributes are allowed. See the discussion under
EXT-X-DATERANGE (Section 4.4.5.1).
A client with specific knowledge of the presentation rules for an
asset MAY override restrictions specified by the X-RESTRICT attribute
if such an action is consistent with those rules.
For an Interstitial EXT-X-DATERANGE tag, the action whose trigger
time is controlled by the CUE attribute is the playback of the
interstitial.
An Interstitial whose EXT-X-DATERANGE tag does not contain a CUE
attribute SHOULD be scheduled for playback at the start of the Date
Range.
Multiple interstitials that are scheduled for the same time SHOULD be
played in the order that their EXT-X-DATERANGE tags appear in the
Playlist. In that case, X-RESUME-OFFSET values are cumulative.
Multiple interstitials that are scheduled for the same time MUST
occur in the same order in all Media Playlists of a Multivariant
Playlist.
If present, the duration (or planned duration) of the Date Range
SHOULD be the duration of the interstitial asset(s), even if a CUE
attribute allows the interstitial to start at some time other than
the START-DATE.
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D.3. Interstitial query parameters
Packagers producing Interstitial EXT-X-DATERANGE tags SHOULD ensure
that X-ASSET-URI and X-ASSET-LIST requests contain an
_HLS_interstitial_id query parameter whose value is the (quoted) ID
attribute value of the EXT-X-DATERANGE tag. This supports
interoperability between content vendors and decisioning servers.
Certain clients support setting the X-PLAYBACK-SESSION-ID request
header with a common, globally-unique value on every HTTP request
associated with a particular playback session. Such clients SHOULD
add an _HLS_primary_id query parameter to interstitial requests whose
value matches the X-PLAYBACK-SESSION-ID of the primary playback
session. This provides useful context for decisioning servers.
Clients that cannot set the X-PLAYBACK-SESSION-ID request header
SHOULD create a globally-unique value for every primary playback
session, and provide this value as an _HLS_primary_id query parameter
on both the request for the primary asset and interstitial requests
made on behalf of that asset.
Interstitial requests are X-ASSET-URI requests, X-ASSET-LIST
requests, and requests for a URI from an X-ASSET-LIST Asset-
Description JSON object.
Clients starting playback of a live stream in an interstitial SHOULD
ensure that X-ASSET-LIST requests contain an _HLS_start_offset query
parameter whose value is the offset in seconds of the playback start
point from the beginning of the interstitial. This allows servers to
customize interstitial content based on the starting offset.
D.4. Client Behavior
If an interstitial specifies a non-zero resume offset and the user
tries to seek to a time between the start of the interstitial and its
resumption point on the primary asset timeline, the client SHOULD
begin playback from the start of the interstitial.
If a request for either an interstitial asset URI or an asset list
URI returns an error, the client SHOULD cancel playback of the
interstitial with a resume offset of 0.
If the JSON object returned by the asset list URI has an empty array
as the value of the "ASSETS" key, the client SHOULD apply the resume
offset without playing any interstitial content.
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Clients SHOULD allow a generous amount of time (up to a minute) for a
server to respond to requests for interstitial assets or asset lists,
to enable the server to perform back-end decisioning. Servers MUST
respond quickly enough to avoid playback disruptions on the client.
D.5. Example: Interstitial EXT-X-DATERANGE
In this playlist an EXT-X-DATERANGE tag schedules a 15-second ad to
play four seconds into a six-second primary asset. The client will
play the interstitial and then resume playback of the primary asset
where it left off. Seeking and scanning forward will be disabled
during interstitial playback. The EXT-X-DATERANGE tag includes a
vendor-defined beacon attribute that can be processed by the client.
#EXTM3U
#EXT-X-TARGETDURATION:6
#EXT-X-PROGRAM-DATE-TIME:2020-01-02T21:55:40.000Z
#EXTINF:6,
main1.0.ts
#EXT-X-ENDLIST
#EXT-X-DATERANGE:ID="ad1",CLASS="com.apple.hls.interstitial",
START-DATE="2020-01-02T21:55:44.000Z",DURATION=15.0,
X-ASSET-URI="http://example.com/ad1.m3u8",X-RESUME-OFFSET=0,
X-RESTRICT="SKIP,JUMP",X-COM-EXAMPLE-BEACON=123
Author's Address
Roger Pantos (editor)
Apple Inc.
Cupertino, California
United States
Email: http-live-streaming-review@group.apple.com
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