Matroska Codec
draft-ietf-cellar-codec-03

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Last updated 2019-10-27
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cellar                                                         S. Lhomme
Internet-Draft                                                          
Intended status: Informational                                 M. Bunkus
Expires: 29 April 2020                                                  
                                                                 D. Rice
                                                         27 October 2019

                             Matroska Codec
                       draft-ietf-cellar-codec-03

Abstract

   This document defines the Matroska codec mappings, including the
   codec ID, layout of data in a "Block Element" and in an optional
   "CodecPrivate Element".

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 29 April 2020.

Copyright Notice

   Copyright (c) 2019 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.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Status of this document . . . . . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Notations and Conventions . . . . . . . . . . . . . . . . . .   5
   6.  Codec Mappings  . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Defining Matroska Codec Support . . . . . . . . . . . . .   5
       6.1.1.  Codec ID  . . . . . . . . . . . . . . . . . . . . . .   5
       6.1.2.  Codec Name  . . . . . . . . . . . . . . . . . . . . .   6
       6.1.3.  Description . . . . . . . . . . . . . . . . . . . . .   7
       6.1.4.  Initialization  . . . . . . . . . . . . . . . . . . .   7
       6.1.5.  Codec BlockAdditions  . . . . . . . . . . . . . . . .   7
       6.1.6.  Citation  . . . . . . . . . . . . . . . . . . . . . .   8
       6.1.7.  Deprecation Date  . . . . . . . . . . . . . . . . . .   8
       6.1.8.  Superseded By . . . . . . . . . . . . . . . . . . . .   8
     6.2.  Recommendations for the Creation of New Codec
           Mappings  . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.3.  Video Codec Mappings  . . . . . . . . . . . . . . . . . .   8
       6.3.1.  V_MS/VFW/FOURCC . . . . . . . . . . . . . . . . . . .   9
       6.3.2.  V_UNCOMPRESSED  . . . . . . . . . . . . . . . . . . .   9
       6.3.3.  V_MPEG4/ISO/SP  . . . . . . . . . . . . . . . . . . .   9
       6.3.4.  V_MPEG4/ISO/ASP . . . . . . . . . . . . . . . . . . .  10
       6.3.5.  V_MPEG4/ISO/AP  . . . . . . . . . . . . . . . . . . .  10
       6.3.6.  V_MPEG4/MS/V3 . . . . . . . . . . . . . . . . . . . .  10
       6.3.7.  V_MPEG1 . . . . . . . . . . . . . . . . . . . . . . .  10
       6.3.8.  V_MPEG2 . . . . . . . . . . . . . . . . . . . . . . .  11
       6.3.9.  V_REAL/RV10 . . . . . . . . . . . . . . . . . . . . .  11
       6.3.10. V_REAL/RV20 . . . . . . . . . . . . . . . . . . . . .  11
       6.3.11. V_REAL/RV30 . . . . . . . . . . . . . . . . . . . . .  12
       6.3.12. V_REAL/RV40 . . . . . . . . . . . . . . . . . . . . .  12
       6.3.13. V_QUICKTIME . . . . . . . . . . . . . . . . . . . . .  12
       6.3.14. V_THEORA  . . . . . . . . . . . . . . . . . . . . . .  13
       6.3.15. V_PRORES  . . . . . . . . . . . . . . . . . . . . . .  13
       6.3.16. V_VP8 . . . . . . . . . . . . . . . . . . . . . . . .  14
       6.3.17. V_VP9 . . . . . . . . . . . . . . . . . . . . . . . .  14
       6.3.18. V_FFV1  . . . . . . . . . . . . . . . . . . . . . . .  14
     6.4.  Audio Codec Mappings  . . . . . . . . . . . . . . . . . .  15
       6.4.1.  A_MPEG/L3 . . . . . . . . . . . . . . . . . . . . . .  15
       6.4.2.  A_MPEG/L2 . . . . . . . . . . . . . . . . . . . . . .  15
       6.4.3.  A_MPEG/L1 . . . . . . . . . . . . . . . . . . . . . .  15
       6.4.4.  A_PCM/INT/BIG . . . . . . . . . . . . . . . . . . . .  16
       6.4.5.  A_PCM/INT/LIT . . . . . . . . . . . . . . . . . . . .  16
       6.4.6.  A_PCM/FLOAT/IEEE  . . . . . . . . . . . . . . . . . .  16
       6.4.7.  A_MPC . . . . . . . . . . . . . . . . . . . . . . . .  16
       6.4.8.  A_AC3 . . . . . . . . . . . . . . . . . . . . . . . .  17
       6.4.9.  A_AC3/BSID9 . . . . . . . . . . . . . . . . . . . . .  17

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       6.4.10. A_AC3/BSID10  . . . . . . . . . . . . . . . . . . . .  17
       6.4.11. A_ALAC  . . . . . . . . . . . . . . . . . . . . . . .  18
       6.4.12. A_DTS . . . . . . . . . . . . . . . . . . . . . . . .  18
       6.4.13. A_DTS/EXPRESS . . . . . . . . . . . . . . . . . . . .  18
       6.4.14. A_DTS/LOSSLESS  . . . . . . . . . . . . . . . . . . .  18
       6.4.15. A_VORBIS  . . . . . . . . . . . . . . . . . . . . . .  19
       6.4.16. A_FLAC  . . . . . . . . . . . . . . . . . . . . . . .  19
       6.4.17. AREAL/144 . . . . . . . . . . . . . . . . . . . . . .  19
       6.4.18. AREAL/288 . . . . . . . . . . . . . . . . . . . . . .  19
       6.4.19. A_REAL/COOK . . . . . . . . . . . . . . . . . . . . .  20
       6.4.20. A_REAL/SIPR . . . . . . . . . . . . . . . . . . . . .  20
       6.4.21. A_REAL/RALF . . . . . . . . . . . . . . . . . . . . .  20
       6.4.22. A_REAL/ATRC . . . . . . . . . . . . . . . . . . . . .  21
       6.4.23. A_MS/ACM  . . . . . . . . . . . . . . . . . . . . . .  21
       6.4.24. A_AAC/MPEG2/MAIN  . . . . . . . . . . . . . . . . . .  21
       6.4.25. A_AAC/MPEG2/LC  . . . . . . . . . . . . . . . . . . .  21
       6.4.26. A_AAC/MPEG2/LC/SBR  . . . . . . . . . . . . . . . . .  22
       6.4.27. A_AAC/MPEG2/SSR . . . . . . . . . . . . . . . . . . .  22
       6.4.28. A_AAC/MPEG4/MAIN  . . . . . . . . . . . . . . . . . .  22
       6.4.29. A_AAC/MPEG4/LC  . . . . . . . . . . . . . . . . . . .  23
       6.4.30. A_AAC/MPEG4/LC/SBR  . . . . . . . . . . . . . . . . .  23
       6.4.31. A_AAC/MPEG4/SSR . . . . . . . . . . . . . . . . . . .  23
       6.4.32. A_AAC/MPEG4/LTP . . . . . . . . . . . . . . . . . . .  23
       6.4.33. A_QUICKTIME . . . . . . . . . . . . . . . . . . . . .  24
       6.4.34. A_QUICKTIME/QDMC  . . . . . . . . . . . . . . . . . .  24
       6.4.35. A_QUICKTIME/QDM2  . . . . . . . . . . . . . . . . . .  24
       6.4.36. A_TTA1  . . . . . . . . . . . . . . . . . . . . . . .  25
       6.4.37. A_WAVPACK4  . . . . . . . . . . . . . . . . . . . . .  25
     6.5.  Subtitle Codec Mappings . . . . . . . . . . . . . . . . .  26
       6.5.1.  S_TEXT/UTF8 . . . . . . . . . . . . . . . . . . . . .  26
       6.5.2.  S_TEXT/SSA  . . . . . . . . . . . . . . . . . . . . .  26
       6.5.3.  S_TEXT/ASS  . . . . . . . . . . . . . . . . . . . . .  26
       6.5.4.  S_TEXT/USF  . . . . . . . . . . . . . . . . . . . . .  26
       6.5.5.  S_TEXT/WEBVTT . . . . . . . . . . . . . . . . . . . .  26
       6.5.6.  S_IMAGE/BMP . . . . . . . . . . . . . . . . . . . . .  27
       6.5.7.  S_DVBSUB  . . . . . . . . . . . . . . . . . . . . . .  27
       6.5.8.  S_VOBSUB  . . . . . . . . . . . . . . . . . . . . . .  27
       6.5.9.  S_HDMV/PGS  . . . . . . . . . . . . . . . . . . . . .  28
       6.5.10. S_HDMV/TEXTST . . . . . . . . . . . . . . . . . . . .  28
       6.5.11. S_KATE  . . . . . . . . . . . . . . . . . . . . . . .  28
     6.6.  Button Codec Mappings . . . . . . . . . . . . . . . . . .  28
       6.6.1.  B_VOBBTN  . . . . . . . . . . . . . . . . . . . . . .  28
   7.  Subtitles . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  Images Subtitles  . . . . . . . . . . . . . . . . . . . .  29
     7.2.  SRT Subtitles . . . . . . . . . . . . . . . . . . . . . .  32
     7.3.  SSA/ASS Subtitles . . . . . . . . . . . . . . . . . . . .  33
     7.4.  USF Subtitles . . . . . . . . . . . . . . . . . . . . . .  37
     7.5.  WebVTT  . . . . . . . . . . . . . . . . . . . . . . . . .  37

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       7.5.1.  Storage of WebVTT in Matroska . . . . . . . . . . . .  37
       7.5.2.  Examples of transformation  . . . . . . . . . . . . .  38
       7.5.3.  Storage of WebVTT in Matroska vs. WebM  . . . . . . .  41
     7.6.  HDMV presentation graphics subtitles  . . . . . . . . . .  42
       7.6.1.  Storage of HDMV presentation graphics
               subtitles . . . . . . . . . . . . . . . . . . . . . .  42
     7.7.  HDMV text subtitles . . . . . . . . . . . . . . . . . . .  42
       7.7.1.  Storage of HDMV text subtitles  . . . . . . . . . . .  42
     7.8.  Digital Video Broadcasting (DVB) subtitles  . . . . . . .  43
       7.8.1.  Storage of DVB subtitles  . . . . . . . . . . . . . .  44
   8.  Block Additional Mapping  . . . . . . . . . . . . . . . . . .  44
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

1.  Introduction

   Matroska aims to become THE standard of multimedia container formats.
   It stores interleaved and timestamped audio/video/subtitle data using
   various codecs.  To interpret the codec data, a mapping between the
   way the data is stored in Matroska and how it is understood by such a
   codec is necessary.

   This document intends to define this mapping for many commonly used
   codecs in Matroska.

2.  Status of this document

   This document is a work-in-progress specification defining the
   Matroska file format as part of the IETF Cellar working group
   (https://datatracker.ietf.org/wg/cellar/charter/).  It uses basic
   elements and concept already defined in the Matroska specifications
   defined by this workgroup.

3.  Security Considerations

   This document inherits security considerations from the EBML and
   Matroska documents.

4.  IANA Considerations

   To be determined.

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5.  Notations and Conventions

   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.

6.  Codec Mappings

   A "Codec Mapping" is a set of attributes to identify, name, and
   contextualize the format and characteristics of encoded data that can
   be contained within Matroska Clusters.

   Each TrackEntry used within Matroska MUST reference a defined "Codec
   Mapping" using the "Codec ID" to identify and describe the format of
   the encoded data in its associated Clusters.  This "Codec ID" is a
   unique registered identifier that represents the encoding stored
   within the Track.  Certain encodings MAY also require some form of
   codec initialization in order to provide its decoder with context and
   technical metadata.

   The intention behind this list is not to list all existing audio and
   video codecs, but rather to list those codecs that are currently
   supported in Matroska and therefore need a well defined "Codec ID" so
   that all developers supporting Matroska will use the same "Codec ID".
   If you feel we missed support for a very important codec, please tell
   us on our development mailing list (cellar at ietf.org).

6.1.  Defining Matroska Codec Support

   Support for a codec is defined in Matroska with the following values.

6.1.1.  Codec ID

   Each codec supported for storage in Matroska MUST have a unique
   "Codec ID".  Each "Codec ID" MUST be prefixed with the string from
   the following table according to the associated type of the codec.
   All characters of a "Codec ID Prefix" MUST be capital letters (A-Z)
   except for the last character of a "Codec ID Prefix" which MUST be an
   underscore ("_").

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                     +------------+-----------------+
                     | Codec Type | Codec ID Prefix |
                     +============+=================+
                     | Video      | "V_"            |
                     +------------+-----------------+
                     | Audio      | "A_"            |
                     +------------+-----------------+
                     | Subtitle   | "S_"            |
                     +------------+-----------------+
                     | Button     | "B_"            |
                     +------------+-----------------+

                                 Table 1

   Each "Codec ID" MUST include a "Major Codec ID" immediately following
   the "Codec ID Prefix".  A "Major Codec ID" MAY be followed by an
   OPTIONAL "Codec ID Suffix" to communicate a refinement of the "Major
   Codec ID".  If a "Codec ID Suffix" is used, then the "Codec ID" MUST
   include a forward slash ("/") as a separator between the "Major Codec
   ID" and the "Codec ID Suffix".  The "Major Codec ID" MUST be composed
   of only capital letters (A-Z) and numbers (0-9).  The "Codec ID
   Suffix" MUST be composed of only capital letters (A-Z), numbers
   (0-9), underscore ("_"), and forward slash ("/").

   The following table provides examples of valid "Codec IDs" and their
   components:

     +----------+----------+-----------+-----------+-----------------+
     | Codec ID | Major    | Separator | Codec ID  | Codec ID        |
     | Prefix   | Codec ID |           | Suffix    |                 |
     +==========+==========+===========+===========+=================+
     | A_       | AAC      | /         | MPEG2/LC/ | A_AAC/MPEG2/LC/ |
     |          |          |           | SBR       | SBR             |
     +----------+----------+-----------+-----------+-----------------+
     | V_       | MPEG4    | /         | ISO/ASP   | V_MPEG4/ISO/ASP |
     +----------+----------+-----------+-----------+-----------------+
     | V_       | MPEG1    |           |           | V_MPEG1         |
     +----------+----------+-----------+-----------+-----------------+

                                  Table 2

6.1.2.  Codec Name

   Each encoding supported for storage in Matroska MUST have a "Codec
   Name".  The "Codec Name" provides a readable label for the encoding.

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6.1.3.  Description

   An optional description for the encoding.  This value is only
   intended for human consumption.

6.1.4.  Initialization

   Each encoding supported for storage in Matroska MUST have a defined
   Initialization.  The Initialization MUST describe the storage of data
   necessary to initialize the decoder, which MUST be stored within the
   "CodecPrivate Element".  When the Initialization is updated within a
   track then that updated Initialization data MUST be written into the
   "CodecState Element" of the first "Cluster" to require it.  If the
   encoding does not require any form of Initialization then "none" MUST
   be used to define the Initialization and the "CodecPrivate Element"
   SHOULD NOT be written and MUST be ignored.  Data that is defined
   Initialization to be stored in the "CodecPrivate Element" is known as
   "Private Data".

6.1.5.  Codec BlockAdditions

   Additional data that contextualizes or supplements a "Block" can be
   stored within the "BlockAdditional Element" of a "BlockMore Element".
   This "BlockAdditional" data MAY be passed to the associated decoder
   along with the content of the "Block Element".  Each
   "BlockAdditional" is coupled with a "BlockAddID" that identifies the
   kind of data it contains.  The following table defines the meanings
   of "BlockAddID" values.

     +------------+-------------------------------------------------+
     | BlockAddID | Definition                                      |
     | Value      |                                                 |
     +============+=================================================+
     | 0          | Invalid.                                        |
     +------------+-------------------------------------------------+
     | 1          | Indicates that the context of the               |
     |            | "BlockAdditional" data is defined by the        |
     |            | corresponding "Codec Mapping".                  |
     +------------+-------------------------------------------------+
     | 2 or       | "BlockAddID" values of 2 and greater are mapped |
     | greater    | to the "BlockAddIDValue" of the                 |
     |            | "BlockAdditionMapping" of the associated Track. |
     +------------+-------------------------------------------------+

                                 Table 3

   The values of "BlockAddID" that are 2 of greater have no semantic
   meaning, but simply associate the "BlockMore Element" with a

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   "BlockAdditionMapping" of the associated Track.  See the section on
   Block Additional Mappings (#block-additional-mapping) for more
   information.

   The following XML depicts the nested Elements of a "BlockGroup
   Element" with an example of BlockAdditions:

   <BlockGroup> <Block>{Binary data of a VP9 video frame in YUV}</Block> <BlockAdditions> <BlockMore> <BlockAddID>1</BlockAddID> <BlockAdditional> {alpha channel encoding to supplement the VP9 frame} </BlockAdditional> </BlockMore> </BlockAdditions> </BlockGroup>

6.1.6.  Citation

   Documentation of the associated normative and informative references
   for the codec is RECOMMENDED.

6.1.7.  Deprecation Date

   A timestamp, expressed in [RFC3339] that notes when support for the
   "Codec Mapping" within Matroska was deprecated.  If a "Codec Mapping"
   is defined with a "Deprecation Date", then it is RECOMMENDED that
   Matroska writers SHOULD NOT use the "Codec Mapping" after the
   "Deprecation Date".

6.1.8.  Superseded By

   A "Codec Mapping" MAY only be defined with a "Superseded By" value,
   if it has an expressed "Deprecation Date".  If used, the "Superseded
   By" value MUST store the "Codec ID" of another "Codec Mapping" that
   has superseded the "Codec Mapping".

6.2.  Recommendations for the Creation of New Codec Mappings

   Creators of new "Codec Mappings" to be used in the context of
   Matroska:

   *  SHOULD assume that all "Codec Mappings" they create might become
      standardized, public, commonly deployed, or usable across multiple
      implementations.

   *  SHOULD employ meaningful values for "Codec ID" and "Codec Name"
      that they have reason to believe are currently unused.

   *  SHOULD NOT prefix their "Codec ID" with "X_" or similar
      constructs.

   These recommendations are based upon Section 3 of [RFC6648].

6.3.  Video Codec Mappings

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6.3.1.  V_MS/VFW/FOURCC

   Codec ID: "V_MS/VFW/FOURCC"

   Codec Name: Microsoft (TM) Video Codec Manager (VCM)

   Description: The private data contains the VCM structure
   BITMAPINFOHEADER including the extra private bytes, as defined by
   Microsoft (https://msdn.microsoft.com/en-us/library/windows/desktop/
   dd318229(v=vs.85).aspx).  The data are stored in little endian format
   (like on IA32 machines).  Where is the Huffman table stored in
   HuffYUV, not AVISTREAMINFO ??? And the FourCC, not in
   AVISTREAMINFO.fccHandler ???

   Initialization: "Private Data" contains the VCM structure
   BITMAPINFOHEADER including the extra private bytes, as defined by
   Microsoft in https://msdn.microsoft.com/en-
   us/library/windows/desktop/dd183376(v=vs.85).aspx
   (https://msdn.microsoft.com/en-us/library/windows/desktop/
   dd183376(v=vs.85).aspx).

   Citation: https://msdn.microsoft.com/en-us/library/windows/desktop/
   dd183376(v=vs.85).aspx (https://msdn.microsoft.com/en-
   us/library/windows/desktop/dd183376(v=vs.85).aspx)

6.3.2.  V_UNCOMPRESSED

   Codec ID: V_UNCOMPRESSED

   Codec Name: Video, raw uncompressed video frames

   Description: All details about the used color specs and bit depth are
   to be put/read from the KaxCodecColourSpace elements.

   Initialization: none

6.3.3.  V_MPEG4/ISO/SP

   Codec ID: V_MPEG4/ISO/SP

   Codec Name: MPEG4 ISO simple profile (DivX4)

   Description: Stream was created via improved codec API (UCI) or even
   transmuxed from AVI (no b-frames in Simple Profile), frame order is
   coding order.

   Initialization: none

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6.3.4.  V_MPEG4/ISO/ASP

   Codec ID: V_MPEG4/ISO/ASP

   Codec Name: MPEG4 ISO advanced simple profile (DivX5, XviD, FFMPEG)

   Description: Stream was created via improved codec API (UCI) or
   transmuxed from MP4, not simply transmuxed from AVI.  Note there are
   differences how b-frames are handled in these native streams, when
   being compared to a VfW created stream, as here there are "no" dummy
   frames inserted, the frame order is exactly the same as the coding
   order, same as in MP4 streams.

   Initialization: none

6.3.5.  V_MPEG4/ISO/AP

   Codec ID: V_MPEG4/ISO/AP

   Codec Name: MPEG4 ISO advanced profile

   Description: Stream was created via improved codec API (UCI) or
   transmuxed from MP4, not simply transmuxed from AVI.  Note there are
   differences how b-frames are handled in these native streams, when
   being compared to a VfW created stream, as here there are "no" dummy
   frames inserted, the frame order is exactly the same as the coding
   order, same as in MP4 streams.

   Initialization: none

6.3.6.  V_MPEG4/MS/V3

   Codec ID: V_MPEG4/MS/V3

   Codec Name: Microsoft (TM) MPEG4 V3

   Description: Microsoft (TM) MPEG4 V3 and derivates, means DivX3,
   Angelpotion, SMR, etc.; stream was created using VfW codec or
   transmuxed from AVI; note that V1/V2 are covered in VfW compatibility
   mode.

   Initialization: none

6.3.7.  V_MPEG1

   Codec ID: V_MPEG1

   Codec Name: MPEG 1

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   Description: The Matroska video stream will contain a demuxed
   Elementary Stream (ES), where block boundaries are still to be
   defined.  Its RECOMMENDED to use MPEG2MKV.exe for creating those
   files, and to compare the results with self-made implementations

   Initialization: none

6.3.8.  V_MPEG2

   Codec ID: V_MPEG2

   Codec Name: MPEG 2

   Description: The Matroska video stream will contain a demuxed
   Elementary Stream (ES), where block boundaries are still to be
   defined.  Its RECOMMENDED to use MPEG2MKV.exe for creating those
   files, and to compare the results with self-made implementations

   Initialization: none

6.3.9.  V_REAL/RV10

   Codec ID: V_REAL/RV10

   Codec Name: RealVideo 1.0 aka RealVideo 5

   Description: Individual slices from the Real container are combined
   into a single frame.

   Initialization: The "Private Data" contains a "real_video_props_t"
   structure in Big Endian byte order as found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.3.10.  V_REAL/RV20

   Codec ID: V_REAL/RV20

   Codec Name: RealVideo G2 and RealVideo G2+SVT

   Description: Individual slices from the Real container are combined
   into a single frame.

   Initialization: The "Private Data" contains a "real_video_props_t"
   structure in Big Endian byte order as found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

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6.3.11.  V_REAL/RV30

   Codec ID: V_REAL/RV30

   Codec Name: RealVideo 8

   Description: Individual slices from the Real container are combined
   into a single frame.

   Initialization: The "Private Data" contains a "real_video_props_t"
   structure in Big Endian byte order as found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.3.12.  V_REAL/RV40

   Codec ID: V_REAL/RV40

   Codec Name: rv40 : RealVideo 9

   Description: Individual slices from the Real container are combined
   into a single frame.

   Initialization: The "Private Data" contains a "real_video_props_t"
   structure in Big Endian byte order as found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.3.13.  V_QUICKTIME

   Codec ID: V_QUICKTIME

   Codec Name: Video taken from QuickTime(TM) files

   Description: Several codecs as stored in QuickTime, e.g.  Sorenson or
   Cinepak.

   Initialization: The "Private Data" contains all additional data that
   is stored in the 'stsd' (sample description) atom in the QuickTime
   file *after* the mandatory video descriptor structure (starting with
   the size and FourCC fields).  For an explanation of the QuickTime
   file format read QuickTime File Format Specification
   (https://developer.apple.com/library/mac/documentation/QuickTime/
   QTFF/QTFFPreface/qtffPreface.html).

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6.3.14.  V_THEORA

   Codec ID: V_THEORA

   Codec Name: Theora

   Initialization: The "Private Data" contains the first three Theora
   packets in order.  The lengths of the packets precedes them.  The
   actual layout is:

   *  Byte 1: number of distinct packets '"#p"' minus one inside the
      CodecPrivate block.  This MUST be '2' for current (as of
      2016-07-08) Theora headers.

   *  Bytes 2..n: lengths of the first '"#p"' packets, coded in Xiph-
      style lacing.  The length of the last packet is the length of the
      CodecPrivate block minus the lengths coded in these bytes minus
      one.

   *  Bytes n+1..: The Theora identification header, followed by the
      commend header followed by the codec setup header.  Those are
      described in the Theora specs (http://www.theora.org/doc/
      Theora.pdf).

6.3.15.  V_PRORES

   Codec ID: V_PRORES

   Codec Name: Apple ProRes

   Initialization: The "Private Data" contains the FourCC as found in
   MP4 movies:

   *  ap4x: ProRes 4444 XQ

   *  ap4h: ProRes 4444

   *  apch: ProRes 422 High Quality

   *  apcn: ProRes 422 Standard Definition

   *  apcs: ProRes 422 LT

   *  apco: ProRes 422 Proxy

   *  aprh: ProRes RAW High Quality

   *  aprn: ProRes RAW Standard Definition

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   this page for more technical details on ProRes
   (http://wiki.multimedia.cx/index.php?title=Apple_ProRes#Frame_layout)

6.3.16.  V_VP8

   Codec ID: V_VP8

   Codec Name: VP8 Codec format

   Description: VP8 is an open and royalty free video compression format
   developed by Google and created by On2 Technologies as a successor to
   VP7.  [RFC6386]

   Codec BlockAdditions: A single-channel encoding of an alpha channel
   MAY be stored in "BlockAdditions".  The "BlockAddId" of the
   "BlockMore" containing these data MUST be 1.

   Initialization: none

6.3.17.  V_VP9

   Codec ID: V_VP9

   Codec Name: VP9 Codec format

   Description: VP9 is an open and royalty free video compression format
   developed by Google as a successor to VP8.  Draft VP9 Bitstream and
   Decoding Process Specification (https://www.webmproject.org/vp9/)

   Codec BlockAdditions: A single-channel encoding of an alpha channel
   MAY be stored in "BlockAdditions".  The "BlockAddId" of the
   "BlockMore" containing these data MUST be 1.

   Initialization: none

6.3.18.  V_FFV1

   Codec ID: V_FFV1

   Codec Name: FF Video Codec 1

   Description: FFV1 is a lossless intra-frame video encoding format
   designed to efficiently compress video data in a variety of pixel
   formats.  Compared to uncompressed video, FFV1 offers storage
   compression, frame fixity, and self-description, which makes FFV1
   useful as a preservation or intermediate video format.  Draft FFV1
   Specification (https://datatracker.ietf.org/doc/draft-ietf-cellar-
   ffv1/)

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   Initialization: For FFV1 versions 0 or 1, "Private Data" SHOULD NOT
   be written.  For FFV1 version 3 or greater, the "Private Data" MUST
   contain the FFV1 Configuration Record structure, as defined in
   https://tools.ietf.org/html/draft-ietf-cellar-ffv1-04#section-4.2
   (https://tools.ietf.org/html/draft-ietf-cellar-ffv1-04#section-4.2),
   and no other data.

6.4.  Audio Codec Mappings

6.4.1.  A_MPEG/L3

   Codec ID: A_MPEG/L3

   Codec Name: MPEG Audio 1, 2, 2.5 Layer III

   Description: The data contain everything needed for playback in the
   MPEG Audio header of each frame.  Corresponding ACM wFormatTag :
   0x0055

   Initialization: none

6.4.2.  A_MPEG/L2

   Codec ID: A_MPEG/L2

   Codec Name: MPEG Audio 1, 2 Layer II

   Description: The data contain everything needed for playback in the
   MPEG Audio header of each frame.  Corresponding ACM wFormatTag :
   0x0050

   Initialization: none

6.4.3.  A_MPEG/L1

   Codec ID: A_MPEG/L1

   Codec Name: MPEG Audio 1, 2 Layer I

   Description: The data contain everything needed for playback in the
   MPEG Audio header of each frame.  Corresponding ACM wFormatTag :
   0x0050

   Initialization: none

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6.4.4.  A_PCM/INT/BIG

   Codec ID: A_PCM/INT/BIG

   Codec Name: PCM Integer Big Endian

   Description: The audio bit depth MUST be read and set from the
   "BitDepth Element".  Audio samples MUST be considered as signed
   values, except if the audio bit depth is "8" which MUST be
   interpreted as unsigned values.  Corresponding ACM wFormatTag : ???

   Initialization: none

6.4.5.  A_PCM/INT/LIT

   Codec ID: A_PCM/INT/LIT

   Codec Name: PCM Integer Little Endian

   Description: The audio bit depth MUST be read and set from the
   "BitDepth Element".  Audio samples MUST be considered as signed
   values, except if the audio bit depth is "8" which MUST be
   interpreted as unsigned values.  Corresponding ACM wFormatTag :
   0x0001

   Initialization: none

6.4.6.  A_PCM/FLOAT/IEEE

   Codec ID: A_PCM/FLOAT/IEEE

   Codec Name: Floating Point, IEEE compatible

   Description: The audio bit depth MUST be read and set from the
   "BitDepth Element" (32 bit in most cases).  The floats are stored as
   defined in [IEEE.754.1985] and in little endian order.  Corresponding
   ACM wFormatTag : 0x0003

   Initialization: none

6.4.7.  A_MPC

   Codec ID: A_MPC

   Codec Name: MPC (musepack) SV8

   Description: The main developer for musepack has requested that we

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   wait until the SV8 framing has been fully defined for musepack before
   defining how to store it in Matroska.

6.4.8.  A_AC3

   Codec ID: A_AC3

   Codec Name: (Dolby[TM]) AC3

   Description: BSID <= 8 !! The private data is void ??? Corresponding
   ACM wFormatTag : 0x2000 ; channel number have to be read from the
   corresponding audio element

6.4.9.  A_AC3/BSID9

   Codec ID: A_AC3/BSID9

   Codec Name: (Dolby[TM]) AC3

   Description: The ac3 frame header has, similar to the mpeg-audio
   header a version field.  Normal ac3 is defined as bitstream id 8 (5
   Bits, numbers are 0-15).  Everything below 8 is still compatible with
   all decoders that handle 8 correctly.  Everything higher are
   additions that break decoder compatibility.  For the samplerates
   24kHz (00); 22,05kHz (01) and 16kHz (10) the BSID is 9 For the
   samplerates 12kHz (00); 11,025kHz (01) and 8kHz (10) the BSID is 10

   Initialization: none

6.4.10.  A_AC3/BSID10

   Codec ID: A_AC3/BSID10

   Codec Name: (Dolby[TM]) AC3

   Description: The ac3 frame header has, similar to the mpeg-audio
   header a version field.  Normal ac3 is defined as bitstream id 8 (5
   Bits, numbers are 0-15).  Everything below 8 is still compatible with
   all decoders that handle 8 correctly.  Everything higher are
   additions that break decoder compatibility.  For the samplerates
   24kHz (00); 22,05kHz (01) and 16kHz (10) the BSID is 9 For the
   samplerates 12kHz (00); 11,025kHz (01) and 8kHz (10) the BSID is 10

   Initialization: none

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6.4.11.  A_ALAC

   Codec ID: A_ALAC

   Codec Name: ALAC (Apple Lossless Audio Codec)

   Initialization: The "Private Data" contains ALAC's magic cookie (both
   the codec specific configuration as well as the optional channel
   layout information).  Its format is described in ALAC's official
   source code (http://alac.macosforge.org/trac/browser/trunk/
   ALACMagicCookieDescription.txt).

6.4.12.  A_DTS

   Codec ID: A_DTS

   Codec Name: Digital Theatre System

   Description: Supports DTS, DTS-ES, DTS-96/26, DTS-HD High Resolution
   Audio and DTS-HD Master Audio.  The private data is void.
   Corresponding ACM wFormatTag : 0x2001

   Initialization: none

6.4.13.  A_DTS/EXPRESS

   Codec ID: A_DTS/EXPRESS

   Codec Name: Digital Theatre System Express

   Description: DTS Express (a.k.a.  LBR) audio streams.  The private
   data is void.  Corresponding ACM wFormatTag : 0x2001

   Initialization: none

6.4.14.  A_DTS/LOSSLESS

   Codec ID: A_DTS/LOSSLESS

   Codec Name: Digital Theatre System Lossless

   Description: DTS Lossless audio that does not have a core substream.
   The private data is void.  Corresponding ACM wFormatTag : 0x2001

   Initialization: none

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6.4.15.  A_VORBIS

   Codec ID: A_VORBIS

   Codec Name: Vorbis

   Initialization: The "Private Data" contains the first three Vorbis
   packet in order.  The lengths of the packets precedes them.  The
   actual layout is: - Byte 1: number of distinct packets '"#p"' minus
   one inside the CodecPrivate block.  This MUST be '2' for current (as
   of 2016-07-08) Vorbis headers.  - Bytes 2..n: lengths of the first
   '"#p"' packets, coded in Xiph-style lacing.  The length of the last
   packet is the length of the CodecPrivate block minus the lengths
   coded in these bytes minus one.  - Bytes n+1..: The Vorbis
   identification header (https://xiph.org/vorbis/doc/
   Vorbis_I_spec.html), followed by the Vorbis comment header
   (https://xiph.org/vorbis/doc/v-comment.html) followed by the codec
   setup header (https://xiph.org/vorbis/doc/Vorbis_I_spec.html).

6.4.16.  A_FLAC

   Codec ID: A_FLAC

   Codec Name: FLAC (Free Lossless Audio Codec)
   (http://flac.sourceforge.net/)

   Initialization: The "Private Data" contains all the header/metadata
   packets before the first data packet.  These include the first header
   packet containing only the word "fLaC" as well as all metadata
   packets.

6.4.17.  A_REAL/14_4

   Codec ID: A_REAL/14_4

   Codec Name: Real Audio 1

   Initialization: The "Private Data" contains either the
   "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure
   (differentiated by their "version" field; Big Endian byte order) as
   found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.4.18.  A_REAL/28_8

   Codec ID: A_REAL/28_8

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   Codec Name: Real Audio 2

   Initialization: The "Private Data" contains either the
   "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure
   (differentiated by their "version" field; Big Endian byte order) as
   found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.4.19.  A_REAL/COOK

   Codec ID: A_REAL/COOK

   Codec Name: Real Audio Cook Codec (codename: Gecko)

   Initialization: The "Private Data" contains either the
   "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure
   (differentiated by their "version" field; Big Endian byte order) as
   found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.4.20.  A_REAL/SIPR

   Codec ID: A_REAL/SIPR

   Codec Name: Sipro Voice Codec

   Initialization: The "Private Data" contains either the
   "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure
   (differentiated by their "version" field; Big Endian byte order) as
   found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.4.21.  A_REAL/RALF

   Codec ID: A_REAL/RALF

   Codec Name: Real Audio Lossless Format

   Initialization: The "Private Data" contains either the
   "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure
   (differentiated by their "version" field; Big Endian byte order) as
   found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

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6.4.22.  A_REAL/ATRC

   Codec ID: A_REAL/ATRC

   Codec Name: Sony Atrac3 Codec

   Initialization: The "Private Data" contains either the
   "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure
   (differentiated by their "version" field; Big Endian byte order) as
   found in librmff
   (https://github.com/mbunkus/mkvtoolnix/blob/master/lib/librmff/
   librmff.h).

6.4.23.  A_MS/ACM

   Codec ID: A_MS/ACM

   Codec Name: Microsoft(TM) Audio Codec Manager (ACM)

   Description: The data are stored in little endian format (like on
   IA32 machines).

   Initialization: The "Private Data" contains the ACM structure
   WAVEFORMATEX including the extra private bytes, as defined by
   Microsoft
   (http://msdn.microsoft.com/library/default.asp?url=/library/en-
   us/multimed/mmstr_625u.asp).

6.4.24.  A_AAC/MPEG2/MAIN

   Codec ID: A_AAC/MPEG2/MAIN

   Codec Name: MPEG2 Main Profile

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.25.  A_AAC/MPEG2/LC

   Codec ID: A_AAC/MPEG2/LC

   Codec Name: Low Complexity

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   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.26.  A_AAC/MPEG2/LC/SBR

   Codec ID: A_AAC/MPEG2/LC/SBR

   Codec Name: Low Complexity with Spectral Band Replication

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.27.  A_AAC/MPEG2/SSR

   Codec ID: A_AAC/MPEG2/SSR

   Codec Name: Scalable Sampling Rate

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.28.  A_AAC/MPEG4/MAIN

   Codec ID: A_AAC/MPEG4/MAIN

   Codec Name: MPEG4 Main Profile

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

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6.4.29.  A_AAC/MPEG4/LC

   Codec ID: A_AAC/MPEG4/LC

   Codec Name: Low Complexity

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.30.  A_AAC/MPEG4/LC/SBR

   Codec ID: A_AAC/MPEG4/LC/SBR

   Codec Name: Low Complexity with Spectral Band Replication

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.31.  A_AAC/MPEG4/SSR

   Codec ID: A_AAC/MPEG4/SSR

   Codec Name: Scalable Sampling Rate

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS
   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.32.  A_AAC/MPEG4/LTP

   Codec ID: A_AAC/MPEG4/LTP

   Codec Name: Long Term Prediction

   Description: Channel number and sample rate have to be read from the
   corresponding audio element.  Audio stream is stripped from ADTS

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   headers and normal Matroska frame based muxing scheme is applied.
   AAC audio always uses wFormatTag 0xFF.

   Initialization: none

6.4.33.  A_QUICKTIME

   Codec ID: A_QUICKTIME

   Codec Name: Audio taken from QuickTime(TM) files

   Description: Several codecs as stored in QuickTime, e.g.  QDesign
   Music v1 or v2.

   Initialization: The "Private Data" contains all additional data that
   is stored in the 'stsd' (sample description) atom in the QuickTime
   file *after* the mandatory sound descriptor structure (starting with
   the size and FourCC fields).  For an explanation of the QuickTime
   file format read QuickTime File Format Specification
   (https://developer.apple.com/library/mac/documentation/QuickTime/
   QTFF/QTFFPreface/qtffPreface.html).

6.4.34.  A_QUICKTIME/QDMC

   Codec ID: A_QUICKTIME/QDMC

   Codec Name: QDesign Music

   Description:

   Initialization: The "Private Data" contains all additional data that
   is stored in the 'stsd' (sample description) atom in the QuickTime
   file *after* the mandatory sound descriptor structure (starting with
   the size and FourCC fields).  For an explanation of the QuickTime
   file format read QuickTime File Format Specification
   (https://developer.apple.com/library/mac/documentation/QuickTime/
   QTFF/QTFFPreface/qtffPreface.html).

   Superseded By: A_QUICKTIME

6.4.35.  A_QUICKTIME/QDM2

   Codec ID: A_QUICKTIME/QDM2

   Codec Name: QDesign Music v2

   Description:

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   Initialization: The "Private Data" contains all additional data that
   is stored in the 'stsd' (sample description) atom in the QuickTime
   file *after* the mandatory sound descriptor structure (starting with
   the size and FourCC fields).  For an explanation of the QuickTime
   file format read QuickTime File Format Specification
   (https://developer.apple.com/library/mac/documentation/QuickTime/
   QTFF/QTFFPreface/qtffPreface.html).

   Superseded By: A_QUICKTIME

6.4.36.  A_TTA1

   Codec ID: A_TTA1

   Codec Name: The True Audio (http://tausoft.org/) lossless audio
   compressor

   Description: TTA format description (http://tausoft.org/wiki/
   True_Audio_Codec_Format) Each frame is kept intact, including the
   CRC32.  The header and seektable are dropped.  SamplingFrequency,
   Channels and BitDepth are used in the TrackEntry. wFormatTag = 0x77A1

   Initialization: none

6.4.37.  A_WAVPACK4

   Codec ID: A_WAVPACK4

   Codec Name: WavPack (http://www.wavpack.com/) lossless audio
   compressor

   Description: The Wavpack packets consist of a stripped header
   followed by the frame data.  For multi-track (> 2 tracks) a frame
   consists of many packets.  For more details, check the WavPack muxing
   description (wavpack.html).

   Codec BlockAdditions: For hybrid "A_WAVPACK4" encodings (that include
   a lossy encoding with a supplemental correction to produce a lossless
   encoding), the correction part is stored in BlockAdditional.  The
   "BlockAddId" of the "BlockMore" containing these data MUST be 1.

   Initialization: none

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6.5.  Subtitle Codec Mappings

6.5.1.  S_TEXT/UTF8

   Codec ID: S_TEXT/UTF8

   Codec Name: UTF-8 Plain Text

   Description: Basic text subtitles.  For more information, please look
   at the Subtitles section (#subtitles).

6.5.2.  S_TEXT/SSA

   Codec ID: S_TEXT/SSA

   Codec Name: Subtitles Format

   Description: The [Script Info] and [V4 Styles] sections are stored in
   the codecprivate.  Each event is stored in its own Block.  For more
   information, see the SSA/ASS section in Subtitles (#subtitles).

6.5.3.  S_TEXT/ASS

   Codec ID: S_TEXT/ASS

   Codec Name: Advanced Subtitles Format

   Description: The [Script Info] and [V4 Styles] sections are stored in
   the codecprivate.  Each event is stored in its own Block.  For more
   information, see the SSA/ASS section in Subtitles (#subtitles).

6.5.4.  S_TEXT/USF

   Codec ID: S_TEXT/USF

   Codec Name: Universal Subtitle Format

   Description: This is mostly defined, but not typed out yet.  It will
   first be available on the USF specification in Subtitles
   (#subtitles).

6.5.5.  S_TEXT/WEBVTT

   Codec ID: S_TEXT/WEBVTT

   Codec Name: Web Video Text Tracks Format (WebVTT)

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   Description: Advanced text subtitles.  For more information, see the
   WebVTT section in Subtitles (#subtitles).

6.5.6.  S_IMAGE/BMP

   Codec ID: S_IMAGE/BMP

   Codec Name: Bitmap

   Description: Basic image based subtitle format; The subtitles are
   stored as images, like in the DVD.  The timestamp in the block header
   of Matroska indicates the start display time, the duration is set
   with the Duration element.  The full data for the subtitle bitmap is
   stored in the Block's data section.

6.5.7.  S_DVBSUB

   Codec ID: S_DVBSUB

   Codec Name: Digital Video Broadcasting (DVB) subtitles

   Description: This is the graphical subtitle format used in the
   Digital Video Broadcasting standard.  For more information, see the
   Digital Video Broadcasting (DVB) section in Subtitles (#subtitles).

6.5.8.  S_VOBSUB

   Codec ID: S_VOBSUB

   Codec Name: VobSub subtitles

   Description: The same subtitle format used on DVDs.  Supported is
   only format version 7 and newer.  VobSubs consist of two files, the
   .idx containing information, and the .sub, containing the actual
   data.  The .idx file is stripped of all empty lines, of all comments
   and of lines beginning with "alt:" or "langidx:".  The line beginning
   with "id:" SHOULD be transformed into the appropriate Matroska track
   language element and is discarded.  All remaining lines but the ones
   containing timestamps and file positions are put into the
   "CodecPrivate" element.

   For each line containing the timestamp and file position data is read
   from the appropriate position in the .sub file.  This data consists
   of a MPEG program stream which in turn contains SPU packets.  The
   MPEG program stream data is discarded, and each SPU packet is put
   into one Matroska frame.

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6.5.9.  S_HDMV/PGS

   Codec ID: S_HDMV/PGS

   Codec Name: HDMV presentation graphics subtitles (PGS)

   Description: This is the graphical subtitle format used on Blu-rays.
   For more information, see HDMV text presentation in Subtitles
   (#subtitles).

6.5.10.  S_HDMV/TEXTST

   Codec ID: S_HDMV/TEXTST

   Codec Name: HDMV text subtitles

   Description: This is the textual subtitle format used on Blu-rays.
   For more information, see HDMV graphics presentation in Subtitles
   (#subtitles).

6.5.11.  S_KATE

   Codec ID: S_KATE

   Codec Name: Karaoke And Text Encapsulation

   Description: A subtitle format developed for ogg.  The mapping for
   Matroska is described on the Xiph wiki
   (http://wiki.xiph.org/index.php/OggKate#Matroska_mapping).  As for
   Theora and Vorbis, Kate headers are stored in the private data as
   xiph-laced packets.

6.6.  Button Codec Mappings

6.6.1.  B_VOBBTN

   Codec ID: B_VOBBTN

   Codec Name: VobBtn Buttons

   Description: Based on MPEG/VOB PCI packets
   (http://dvd.sourceforge.net/dvdinfo/pci_pkt.html).  The file contains
   a header consisting of the string "butonDVD" followed by the width
   and height in pixels (16 bits integer each) and 4 reserved bytes.
   The rest is full PCI packets (http://dvd.sourceforge.net/dvdinfo/
   pci_pkt.html).

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7.  Subtitles

   Because Matroska is a general container format, we try to avoid
   specifying the formats to store in it.  This type of work is really
   outside of the scope of a container-only format.  However, because
   the use of subtitles in A/V containers has been so limited (with the
   exception of DVD) we are taking the time to specify how to store some
   of the more common subtitle formats in Matroska.  This is being done
   to help facilitate their growth.  Otherwise, incompatibilities could
   prevent the standardization and use of subtitle storage.

   This page is not meant to be a complete listing of all subtitle
   formats that will be used in Matroska, it is only meant to be a guide
   for the more common, current formats.  It is possible that we will
   add future formats to this page as they are created, but it is not
   likely as any other new subtitle format designer would likely have
   their own specifications.  Any specification listed here SHOULD be
   strictly adhered to or it SHOULD NOT use the corresponding Codec ID.

   Here is a list of pointers for storing subtitles in Matroska:

   *  Any Matroska file containing only subtitles SHOULD use the
      extension ".mks".

   *  As a general rule of thumb for all codecs, information that is
      global to an entire stream SHOULD be stored in the CodecPrivate
      element.

   *  Start and stop timestamps that are used in a timestamps native
      storage format SHOULD be removed when being placed in Matroska as
      they could interfere if the file is edited afterwards.  Instead,
      the Blocks timestamp and Duration SHOULD be used to say when the
      timestamp is displayed.

   *  Because a "subtitle" stream is actually just an overlay stream,
      anything with a transparency layer could be use, including video.

7.1.  Images Subtitles

   The first image format that is a goal to import into Matroska is the
   VobSub subtitle format.  This subtitle type is generated by exporting
   the subtitles from a DVD.

   The requirement for muxing VobSub into Matroska is v7 subtitles (see
   first line of the .IDX file).  If the version is smaller, you must
   remux them using the SubResync utility from VobSub 2.23 (or MPC) into
   v7 format.  Generally any newly created subs will be in v7 format.

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   The .IFO file will not be used at all.

   If there is more than one subtitle stream in the VobSub set, each
   stream will need to be separated into separate tracks for storage in
   Matroska.  E.g. the VobSub file contains streams for both English and
   German subtitles.  Then the resulting Matroska file SHOULD contain
   two tracks.  That way the language information can be 'dropped' and
   mapped to Matroska's language tags.

   The .IDX file is reformatted (see below) and placed in the
   CodecPrivate.

   Each .BMP will be stored in its own Block.  The Timestamp with be
   stored in the Blocks Timestamp and the duration will be stored in the
   Default Duration.

   Here is an example .IDX file:

    # VobSub index file, v7 (do not modify this line!)
    #
    # To repair desynchronization, you can insert gaps this way:
    # (it usually happens after vob id changes)
    #
    # delay: [sign]hh:mm:ss:ms
    #
    # Where:
    # [sign]: +, - (optional)
    # hh: hours (0 <= hh)
    # mm/ss: minutes/seconds (0 <= mm/ss <= 59)
    # ms: milliseconds (0 <= ms <= 999)
    #
    # Note: You can't position a sub before the previous with a negative
    # value.
    #
    # You can also modify timestamps or delete a few subs you don't
    # like. Just make sure they stay in increasing order.

    # Settings

    # Original frame size
    size: 720x480

    # Origin, relative to the upper-left corner, can be overloaded by
    # alignment
    org: 0, 0

    # Image scaling (hor,ver), origin is at the upper-left corner or at
    # the alignment coord (x, y)

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    scale: 100%, 100%

    # Alpha blending
    alpha: 100%

    # Smoothing for very blocky images (use OLD for no filtering)
    smooth: OFF

    # In millisecs
    fadein/out: 50, 50

    # Force subtitle placement relative to (org.x, org.y)
    align: OFF at LEFT TOP

    # For correcting non-progressive desync. (in millisecs or
    # hh:mm:ss:ms)
    # Note: Not effective in DirectVobSub, use "delay: ... " instead.
    time offset: 0

    # ON: displays only forced subtitles, OFF: shows everything
    forced subs: OFF

    # The original palette of the DVD
    palette: 000000, 7e7e7e, fbff8b, cb86f1, 7f74b8, e23f06, 0a48ea, \
    b3d65a, 6b92f1, 87f087, c02081, f8d0f4, e3c411, 382201, e8840b, \
    fdfdfd

    # Custom colors (transp idxs and the four colors)
    custom colors: OFF, tridx: 0000, colors: 000000, 000000, 000000, \
    000000

    # Language index in use
    langidx: 0

    # English
    id: en, index: 0
    # Uncomment next line to activate alternative name in DirectVobSub /
    # Windows Media Player 6.x
    # alt: English
    # Vob/Cell ID: 1, 1 (PTS: 0)
    timestamp: 00:00:01:101, filepos: 000000000
    timestamp: 00:00:08:708, filepos: 000001000

   First, lines beginning with "#" are removed.  These are comments to
   make text file editing easier, and as this is not a text file, they
   aren't needed.

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   Next remove the "langidx" and "id" lines.  These are used to
   differentiate the subtitle streams and define the language.  As the
   streams will be stored separately anyway, there is no need to
   differentiate them here.  Also, the language setting will be stored
   in the Matroska tags, so there is no need to store it here.

   Finally, the "timestamp" will be used to set the Block's timestamp.
   Once it is set there, there is no need for it to be stored here.
   Also, as it may interfere if the file is edited, it SHOULD NOT be
   stored here.

   Once all of these items are removed, the data to store in the
   CodecPrivate SHOULD look like this:

    size: 720x480
    org: 0, 0
    scale: 100%, 100%
    alpha: 100%
    smooth: OFF
    fadein/out: 50, 50
    align: OFF at LEFT TOP
    time offset: 0
    forced subs: OFF
    palette: 000000, 7e7e7e, fbff8b, cb86f1, 7f74b8, e23f06, 0a48ea, \
    b3d65a, 6b92f1, 87f087, c02081, f8d0f4, e3c411, 382201, e8840b, \
    fdfdfd
    custom colors: OFF, tridx: 0000, colors: 000000, 000000, 000000, \
    000000

   There SHOULD also be two Blocks containing one image each with the
   timestamps "00:00:01:101" and "00:00:08:708".

7.2.  SRT Subtitles

   SRT is perhaps the most basic of all subtitle formats.

   It consists of four parts, all in text..

   1.  A number indicating which subtitle it is in the sequence.  2.
   The time that the subtitle appears on the screen, and then
   disappears.  3.  The subtitle itself.  4.  A blank line indicating
   the start of a new subtitle.

   When placing SRT in Matroska, part 3 is converted to UTF-8 (S_TEXT/
   UTF8) and placed in the data portion of the Block.  Part 2 is used to
   set the timestamp of the Block, and BlockDuration element.  Nothing
   else is used.

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   Here is an example SRT file:

   1
   00:02:17,440 --> 00:02:20,375
   Senator, we're making
   our final approach into Coruscant.

   2
   00:02:20,476 --> 00:02:22,501
   Very good, Lieutenant.

   In this example, the text "Senator, we're making our final approach
   into Coruscant." would be converted into UTF-8 and placed in the
   Block.  The timestamp of the block would be set to "00:02:17,440".
   And the BlockDuration element would be set to "00:00:02,935".

   The same is repeated for the next subtitle.

   Because there are no general settings for SRT, the CodecPrivate is
   left blank.

7.3.  SSA/ASS Subtitles

   SSA stands for Sub Station Alpha.  It's the file format used by the
   popular subtitle editor, SubStation Alpha (http://wiki.multimedia.cx/
   index.php?title=SubStation_Alpha).  This format is widely used by
   fansubbers.

   It allows you to do some advanced display features, like positioning,
   karaoke, style managements...

   For detailed information on SSA/ASS, see the SSA specs
   (http://moodub.free.fr/video/ass-specs.doc).  It includes an SSA
   specs description and the advanced features added by ASS format
   (standing for Advanced SSA).  Because SSA and ASS are so similar,
   they are treated the same here.

   Like SRT, this format is text based with a particular syntax.

   A file consists of 4 or 5 parts, declared ala INI file (but it's not
   an INI !)

   The first, "[Script Info]" contains some information about the
   subtitle file, such as it's title, who created it, type of script and
   a very important one : "PlayResY".  Be careful of this value,
   everything in your script (font size, positioning) is scaled by it.
   Sub Station Alpha uses your desktops Y resolution to write this
   value, so if a friend with a large monitor and a high screen

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   resolution gives you an edited script, you can mess everything up by
   saving the script in SSA with your low-cost monitor.

   The second, "[V4 Styles]", is a list of style definitions.  A style
   describe how will look a text on the screen.  It defines font, font
   size, primary/.../outile colour, position, alignment, etc.

   For example this :

   Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, \
   TertiaryColour, BackColour, Bold, Italic, BorderStyle, Outline, \
   Shadow, Alignment, MarginL, MarginR, MarginV, AlphaLevel, Encoding
   Style: Wolf main,Wolf_Rain,56,15724527,15724527,15724527,4144959,0,\
   0,1,1,2,2,5,5,30,0,0

   The third, "[Events]", is the list of text you want to display at the
   right timing.  You can specify some attribute here.  Like the style
   to use for this event (MUST be defined in the list), the position of
   the text (Left, Right, Vertical Margin), an effect.  Name is mostly
   used by translator to know who said this sentence.  Timing is in
   h:mm:ss.cc (centisec).

   Format: Marked, Start, End, Style, Name, MarginL, MarginR, MarginV, \
   Effect, Text
   Dialogue: Marked=0,0:02:40.65,0:02:41.79,Wolf main,Cher,0000,0000,\
   0000,,Et les enregistrements de ses ondes delta ?
   Dialogue: Marked=0,0:02:42.42,0:02:44.15,Wolf main,autre,0000,0000,\
   0000,,Toujours rien.

   "[Pictures]" or "[Fonts]" part can be found in some SSA file, they
   contains UUE-encoded pictures/font but those features are only used
   by Sub Station Alpha, i.e. no filter (Vobsub/Avery Lee Subtiler
   filter) use them.

   Now, how are they stored in Matroska ?

   *  All text is converted to UTF-8* All the headers are stored in
      CodecPrivate ( Script Info and the Styles list)* Start & End field
      are used to set TimeStamp and the BlockDuration element. the data
      stored is :* Events are stored in the Block in this order:
      ReadOrder, Layer, Style, Name, MarginL, MarginR, MarginV, Effect,
      Text (Layer comes from ASS specs ... it's empty for SSA.)
      "ReadOrder field is needed for the decoder to be able to reorder
      the streamed samples as they were placed originally in the file."

   Here is an example of an SSA file.

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   [Script Info]
   ; This is a Sub Station Alpha v4 script.
   ; For Sub Station Alpha info and downloads,
   ; go to \
   ; [http://www.eswat.demon.co.uk/](http://www.eswat.demon.co.uk/)
   ; or email \
   ; [kotus@eswat.demon.co.uk](mailto:kotus@eswat.demon.co.uk)
   Title: Wolf's rain 2
   Original Script: Anime-spirit Ishin-francais
   Original Translation: Coolman
   Original Editing: Spikewolfwood
   Original Timing: Lord_alucard
   Original Script Checking: Spikewolfwood
   ScriptType: v4.00
   Collisions: Normal
   PlayResY: 1024
   PlayDepth: 0
   Wav: 0, 128697,D:\Alex\Anime\- Fansub -\- TAFF -\WR_-_02_Wav.wav
   Wav: 0, 120692,H:\team truc\WR_-_02.wav
   Wav: 0, 116504,E:\sub\wolf's_rain\WOLF'S RAIN 02.wav
   LastWav: 3
   Timer: 100,0000

   [V4 Styles]
   Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, \
   TertiaryColour, BackColour, Bold, Italic, BorderStyle, Outline, \
   Shadow, Alignment, MarginL, MarginR, MarginV, AlphaLevel, Encoding
   Style: Default,Arial,20,65535,65535,65535,-2147483640,-1,0,1,3,0,2,\
   30,30,30,0,0
   Style: Titre_episode,Akbar,140,15724527,65535,65535,986895,-1,0,1,1,\
   0,3,30,30,30,0,0
   Style: Wolf main,Wolf_Rain,56,15724527,15724527,15724527,4144959,0,\
   0,1,1,2,2,5,5,30,0,0

   [Events]
   Format: Marked, Start, End, Style, Name, MarginL, MarginR, MarginV, \
   Effect, Text
   Dialogue: Marked=0,0:02:40.65,0:02:41.79,Wolf main,Cher,0000,0000,\
   0000,,Et les enregistrements de ses ondes delta ?
   Dialogue: Marked=0,0:02:42.42,0:02:44.15,Wolf main,autre,0000,0000,\
   0000,,Toujours rien.

   Here is what would be placed into the CodecPrivate element.

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   [Script Info]
   ; This is a Sub Station Alpha v4 script.
   ; For Sub Station Alpha info and downloads,
   ; go to \
   ; [http://www.eswat.demon.co.uk/](http://www.eswat.demon.co.uk/)
   ; or email \
   ; [kotus@eswat.demon.co.uk](mailto:kotus@eswat.demon.co.uk)
   Title: Wolf's rain 2
   Original Script: Anime-spirit Ishin-francais
   Original Translation: Coolman
   Original Editing: Spikewolfwood
   Original Timing: Lord_alucard
   Original Script Checking: Spikewolfwood
   ScriptType: v4.00
   Collisions: Normal
   PlayResY: 1024
   PlayDepth: 0
   Wav: 0, 128697,D:\Alex\Anime\- Fansub -\- TAFF -\WR_-_02_Wav.wav
   Wav: 0, 120692,H:\team truc\WR_-_02.wav
   Wav: 0, 116504,E:\sub\wolf's_rain\WOLF'S RAIN 02.wav
   LastWav: 3
   Timer: 100,0000

   [V4 Styles]
   Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, \
   TertiaryColour, BackColour, Bold, Italic, BorderStyle, Outline, \
   Shadow, Alignment, MarginL, MarginR, MarginV, AlphaLevel, Encoding
   Style: Default,Arial,20,65535,65535,65535,-2147483640,-1,0,1,3,0,2,\
   30,30,30,0,0
   Style: Titre_episode,Akbar,140,15724527,65535,65535,986895,-1,0,1,1,\
   0,3,30,30,30,0,0
   Style: Wolf main,Wolf_Rain,56,15724527,15724527,15724527,4144959,0,\
   0,1,1,2,2,5,5,30,0,0

   And here are the two blocks that would be generated.

   Block's timestamp: 00:02:40.650 BlockDuration: 00:00:01.140

   1,,Wolf main,Cher,0000,0000,0000,,Et les enregistrements de ses \
   ondes delta ?

   Block's timestamp: 00:02:42.420 BlockDuration: 00:00:01.730

   2,,Wolf main,autre,0000,0000,0000,,Toujours rien.

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7.4.  USF Subtitles

   Under construction

7.5.  WebVTT

   The "Web Video Text Tracks Format" (short: WebVTT) is developed by
   the World Wide Web Consortium (W3C) (https://www.w3.org/).  Its
   specifications are freely available (https://w3c.github.io/webvtt/).

   The guiding principles for the storage of WebVTT in Matroska are:

   *  Consistency: store data in a similar way to other subtitle codecs

   *  Simplicity: making decoding and remuxing as easy as possible for
      existing infrastructures

   *  Completeness: keeping as much data as possible from the original
      WebVTT file

7.5.1.  Storage of WebVTT in Matroska

7.5.1.1.  CodecID: codec identification

   The CodecID to use is "S_TEXT/WEBVTT".

7.5.1.2.  CodecPrivate: storage of global WebVTT blocks

   This element contains all global blocks before the first subtitle
   entry.  This starts at the ""WEBVTT"" file identification marker but
   excludes the optional byte order mark.

7.5.1.3.  Storage of non-global WebVTT blocks

   Non-global WebVTT blocks (e.g.  "NOTE") before a WebVTT Cue Text are
   stored in Matroska's BlockAddition element together with the Matroska
   Block containing the WebVTT Cue Text these blocks precede (see below
   for the actual format).

7.5.1.4.  Storage of Cues in Matroska blocks

   Each WebVTT Cue Text is stored directly in the Matroska Block.

   A muxer MUST change all WebVTT Cue Timestamps present within the Cue
   Text to be relative to the Matroska Block's timestamp.

   The Cue's start timestamp is used as the Matroska Block's timestamp.

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   The difference between the Cue's end timestamp and its start
   timestamp is used as the Matroska Block's duration.

7.5.1.5.  BlockAdditions: storing non-global WebVTT blocks, Cue Settings
          Lists and Cue identifiers

   Each Matroska Block may be accompanied by one BlockAdditions element.
   Its format is as follows:

   1.  The first line contains the WebVTT Cue Text's optional Cue
       Settings List followed by one line feed character (U+0x000a).
       The Cue Settings List may be empty in which case the line
       consists of the line feed character only.

   2.  The second line contains the WebVTT Cue Text's optional Cue
       Identifier followed by one line feed character (U+0x000a).  The
       line may be empty indicating that there was no Cue Identifier in
       the source file in which case the line consists of the line feed
       character only.

   3.  The third and all following lines contain all WebVTT Comment
       Blocks that precede the current WebVTT Cue Block.  These may be
       absent.

   If there is no Matroska BlockAddition element stored together with
   the Matroska Block then all three components (Cue Settings List, Cue
   Identifier, Cue Comments) MUST be assumed to be absent.

7.5.2.  Examples of transformation

   Here's an example how a WebVTT is transformed.

7.5.2.1.  Example WebVTT file

   Let's take the following example file:

   WEBVTT with text after the signature

   STYLE
   ::cue {
     background-image: linear-gradient(to bottom, dimgray, lightgray);
     color: papayawhip;
   }
   /* Style blocks cannot use blank lines nor "dash dash greater \
   than" */

   NOTE comment blocks can be used between style blocks.

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   STYLE
   ::cue(b) {
     color: peachpuff;
   }

   REGION
   id:bill
   width:40%
   lines:3
   regionanchor:0%,100%
   viewportanchor:10%,90%
   scroll:up

   NOTE
   Notes always span a whole block and can cover multiple
   lines. Like this one.
   An empty line ends the block.

   hello
   00:00:00.000 --> 00:00:10.000
   Example entry 1: Hello <b>world</b>.

   NOTE style blocks cannot appear after the first cue.

   00:00:25.000 --> 00:00:35.000
   Example entry 2: Another entry.
   This one has multiple lines.

   00:01:03.000 --> 00:01:06.500 position:90% align:right size:35%
   Example entry 3: That stuff to the right of the timestamps are cue \
   settings.

   00:03:10.000 --> 00:03:20.000
   Example entry 4: Entries can even include timestamps.
   For example:<00:03:15.000>This becomes visible five seconds
   after the first part.

7.5.2.2.  Example of CodecPrivate

   The resulting CodecPrivate element will look like this:

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   WEBVTT with text after the signature

   STYLE
   ::cue {
     background-image: linear-gradient(to bottom, dimgray, lightgray);
     color: papayawhip;
   }
   /* Style blocks cannot use blank lines nor "dash dash greater \
   than" */

   NOTE comment blocks can be used between style blocks.

   STYLE
   ::cue(b) {
     color: peachpuff;
   }

   REGION
   id:bill
   width:40%
   lines:3
   regionanchor:0%,100%
   viewportanchor:10%,90%
   scroll:up

   NOTE
   Notes always span a whole block and can cover multiple
   lines. Like this one.
   An empty line ends the block.

7.5.2.3.  Storage of Cue 1

   Example Cue 1: timestamp 00:00:00.000, duration 00:00:10.000, Block's
   content:

   Example entry 1: Hello <b>world</b>.

   BlockAddition's content starts with one empty line as there's no Cue
   Settings List:

   hello

7.5.2.4.  Storage of Cue 2

   Example Cue 2: timestamp 00:00:25.000, duration 00:00:10.000, Block's
   content:

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   Example entry 2: Another entry.
   This one has multiple lines.

   BlockAddition's content starts with two empty lines as there's
   neither a Cue Settings List nor a Cue Identifier:

   NOTE style blocks cannot appear after the first cue.

7.5.2.5.  Storage of Cue 3

   Example Cue 3: timestamp 00:01:03.000, duration 00:00:03.500, Block's
   content:

   Example entry 3: That stuff to the right of the timestamps are cue \
   settings.

   BlockAddition's content ends with an empty line as there's no Cue
   Identifier and there were no WebVTT Comment blocks:

   position:90% align:right size:35%

7.5.2.6.  Storage of Cue 4

   Example Cue 4: timestamp 00:03:10.000, duration 00:00:10.000, Block's
   content:

   Example entry 4: Entries can even include timestamps.  For
   example:00:00:05.000 (00:00:05.000)This becomes visible five seconds
   after the first part.

   This Block does not need a BlockAddition as the Cue did not contain
   an Identifier, nor a Settings List, and it wasn't preceded by Comment
   blocks.

7.5.3.  Storage of WebVTT in Matroska vs. WebM

   Note: the storage of WebVTT in Matroska is not the same as the design
   document for storage of WebVTT in WebM.  There are several reasons
   for this including but not limited to: the WebM document is old (from
   February 2012) and was based on an earlier draft of WebVTT and
   ignores several parts that were added to WebVTT later; WebM does
   still not support subtitles at all (http://www.webmproject.org/docs/
   container/); the proposal suggests splitting the information across
   multiple tracks making demuxer's and remuxer's life very difficult.

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7.6.  HDMV presentation graphics subtitles

   The specifications for the HDMV presentation graphics subtitle format
   (short: HDMV PGS) can be found in the document "Blu-ray Disc Read-
   Only Format; Part 3 -- Audio Visual Basic Specifications" in section
   9.14 "HDMV graphics streams".

7.6.1.  Storage of HDMV presentation graphics subtitles

   The CodecID to use is "S_HDMV/PGS".  A CodecPrivate element is not
   used.

7.6.1.1.  Storage of HDMV PGS Segments in Matroska Blocks

   Each HDMV PGS Segment (short: Segment) will be stored in a Matroska
   Block.  A Segment is the data structure described in section 9.14.2.1
   "Segment coding structure and parameters" of the Blu-ray
   specifications.

   Each Segment contains a presentation timestamp.  This timestamp will
   be used as the timestamp for the Matroska Block.

   A Segment is normally shown until a subsequent Segment is
   encountered.  Therefore the Matroska Block MAY have no Duration.  In
   that case a player MUST display a Segment within a Matroska Block
   until the next Segment is encountered.

   A muxer MAY use a Duration, e.g. by calculating the distance between
   two subsequent Segments.  If a Matroska Block has a Duration, a
   player MUST display that Segment only for the duration of the Block's
   Duration.

7.7.  HDMV text subtitles

   The specifications for the HDMV text subtitle format (short: HDMV
   TextST) can be found in the document "Blu-ray Disc Read-Only Format;
   Part 3 -- Audio Visual Basic Specifications" in section 9.15 "HDMV
   text subtitle streams".

7.7.1.  Storage of HDMV text subtitles

   The CodecID to use is "S_HDMV/TEXTST".

   A CodecPrivate Element is required.  It MUST contain the stream's
   Dialog Style Segment as described in section 9.15.4.2 "Dialog Style
   Segment" of the Blu-ray specifications.

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7.7.1.1.  Storage of HDMV TextST Dialog Presentation Segments in
          Matroska Blocks

   Each HDMV Dialog Presentation Segment (short: Segment) will be stored
   in a Matroska Block.  A Segment is the data structure described in
   section 9.15.4.3 "Dialog presentation segment" of the Blu-ray
   specifications.

   Each Segment contains a start and an end presentation timestamp
   (short: start PTS & end PTS).  The start PTS will be used as the
   timestamp for the Matroska Block.  The Matroska Block MUST have a
   Duration, and that Duration is the difference between the end PTS and
   the start PTS.

   A player MUST use the Matroska Block's timestamp and Duration instead
   of the Segment's start and end PTS for determining when and how long
   to show the Segment.

7.7.1.2.  Character set

   When TextST subtitles are stored inside Matroska, the only allowed
   character set is UTF-8.

   Each HDMV text subtitle stream in a Blu-ray can use one of a handful
   of character sets.  This information is not stored in the MPEG2
   Transport Stream itself but in the accompanying Clip Information
   file.

   Therefore a muxer MUST parse the accompanying Clip Information file.
   If the information indicates a character set other than UTF-8, it
   MUST re-encode all text Dialog Presentation Segments from the
   indicated character set to UTF-8 prior to storing them in Matroska.

7.8.  Digital Video Broadcasting (DVB) subtitles

   The specifications for the Digital Video Broadcasting subtitle
   bitstream format (short: DVB subtitles) can be found in the document
   "ETSI EN 300 743 - Digital Video Broadcasting (DVB); Subtitling
   systems".  The storage of DVB subtitles in MPEG transport streams is
   specified in the document "ETSI EN 300 468 - Digital Video
   Broadcasting (DVB); Specification for Service Information (SI) in DVB
   systems".

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7.8.1.  Storage of DVB subtitles

7.8.1.1.  CodecID

   The CodecID to use is "S_DVBSUB".

7.8.1.2.  CodecPrivate

   The CodecPrivate element is five bytes long and has the following
   structure:

   *  2 bytes: composition page ID (bit string, left bit first)

   *  2 bytes: ancillary page ID (bit string, left bit first)

   *  1 byte: subtitling type (bit string, left bit first)

   The semantics of these bytes are the same as the ones described in
   section 6.2.41 "Subtitling descriptor" of ETSI EN 300 468.

7.8.1.3.  Storage of DVB subtitles in Matroska Blocks

   Each Matroska Block consists of one or more DVB Subtitle Segments as
   described in segment 7.2 "Syntax and semantics of the subtitling
   segment" of ETSI EN 300 743.

   Each Matroska Block SHOULD have a Duration indicating how long the
   DVB Subtitle Segments in that Block SHOULD be displayed.

8.  Block Additional Mapping

   Extra data or metadata can be added to each "Block" using
   "BlockAdditional" data.  Each "BlockAdditional" contains a
   "BlockAddID" that identifies the kind of data it contains.  When the
   "BlockAddID" is set to "1" the contents of the "BlockAdditional
   Element" are define by the Codec Mappings defines (see
   Section 6.1.5).  When the "BlockAddID" is set a value greater than
   "1", then the contents of the "BlockAdditional Element" are defined
   by the "BlockAdditionalMapping Element" within the associated "Track
   Element" where the "BlockAddID Element" of "BlockAdditional Element"
   equals the "BlockAddIDValue" of the associated Track's
   "BlockAdditionalMapping Element".  That "BlockAdditionalMapping
   Element" then identifies a particular Block Additional Mapping by the
   "BlockAddIDType".

   The following XML depicts a use of a Block Additional Mapping to
   associate a timecode value with a "Block":

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   <Segment> <!--Mandatory elements ommitted for readability--> <Tracks> <TrackEntry> <TrackNumber>1</TrackNumber> <TrackUID>568001708</TrackUID> <TrackType>1</TrackType> <BlockAdditionalMapping> <BlockAddIDValue>2</BlockAddIDValue><!--arbitrary value used in BlockAddID--> <BlockAddIDName>timecode</BlockAddIDName> <BlockAddIDType>12</BlockAddIDType> </BlockAdditionalMapping> <CodecID>V_FFV1</CodecID> <Video> <PixelWidth>1920</PixelWidth> <PixelHeight>1080</PixelHeight> </Video> </TrackEntry> </Tracks> <Cluster> <Timestamp>3000</Timestamp> <BlockGroup> <Block>{binary video frame}</Block> <BlockAdditions> <BlockMore> <BlockAddID>2</BlockAddID><!--arbitrary value from BlockAdditionalMapping--> <BlockAdditional>01:00:00:00</BlockAdditional> </BlockMore> </BlockAdditions> </BlockGroup> </Cluster> </Segment>

   Block Additional Mappings detail how additional data MAY be stored in
   the "BlockMore Element" with a "BlockAdditionMapping Element" within
   the "Track Element" which identifies the "BlockAdditional" content.
   Block Additional Mappings define the "BlockAddIDType" value reserved
   to identify that type of data as well as providing an optional label
   stored within the "BlockAddIDName Element".  When the Block
   Additional Mapping is dependent on additional contextual information
   then the Mapping SHOULD describe how such additional contextual
   information is stored within the "BlockAddIDExtraData Element".

   The following Block Additional Mappings are defined.

9.  Normative References

   [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>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC6648]  Saint-Andre, P., Crocker, D., and M. Nottingham,
              "Deprecating the "X-" Prefix and Similar Constructs in
              Application Protocols", BCP 178, RFC 6648,
              DOI 10.17487/RFC6648, June 2012,
              <https://www.rfc-editor.org/info/rfc6648>.

   [RFC6386]  Bankoski, J., Koleszar, J., Quillio, L., Salonen, J.,
              Wilkins, P., and Y. Xu, "VP8 Data Format and Decoding
              Guide", RFC 6386, DOI 10.17487/RFC6386, November 2011,
              <https://www.rfc-editor.org/info/rfc6386>.

   [IEEE.754.1985]
              Institute of Electrical and Electronics Engineers,
              "Standard for Binary Floating-Point Arithmetic", August
              1985.

   [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>.

Authors' Addresses

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   Steve Lhomme

   Email: slhomme@matroska.org

   Moritz Bunkus

   Email: moritz@bunkus.org

   Dave Rice

   Email: dave@dericed.com

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