Track Switching in Media over QUIC Transport
draft-gurel-moq-track-switching-00

MOQ                                                             Z. Gurel
Internet-Draft                                        Ozyegin University
Intended status: Standards Track                                A. Begen
Expires: 8 January 2025                                  Networked Media
                                                             7 July 2024

              Track Switching in Media over QUIC Transport
                   draft-gurel-moq-track-switching-00

Abstract

   This document defines a solution for switching tracks in media.  More
   particularly, the solution provides a seamless switching that ensures
   there is no overlapping or gap between the download and/or
   transmission of two tracks when they are alternatives to each other.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 8 January 2025.

Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terms and Definitions . . . . . . . . . . . . . . . . . .   2
     1.2.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Switching Tracks  . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  The Problem and Solution Approaches . . . . . . . . . . .   5
       2.1.1.  Solution 1 (altTrackGroup)  . . . . . . . . . . . . .   6
       2.1.2.  Solution 2 (Switch Track Alias) . . . . . . . . . . .   7
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document outlines a solution for switching tracks in media
   delivery over Media Over QUIC Transport (MOQT) [MoQTransport].
   Switching tracks is necessary for a variety of reasons, such as
   changing the quality, the language of the media, or the type of the
   media (e.g., switching from a video to an audio track).  The solution
   described in this document ensures that there is no overlapping or
   gap between the download and/or transmission of two tracks when they
   are alternatives to each other.

1.1.  Terms and Definitions

   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.

   Client:  The party initiating a MoQ transport session.

   Server:  The party accepting an incoming transport session.

   Endpoint:  A Client or Server.

   Producer:  An endpoint sending media over the network.

   Consumer:  An endpoint receiving media over the network.

   Transport session:  A raw QUIC connection or a WebTransport session.

   Congestion:  Packet loss and queuing caused by degraded or overloaded

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      networks.

   Group:  A temporal sequence of objects.  A group represents a join
      point in a track.

   Object:  An object is an addressable unit whose payload is a sequence
      of bytes.

   Track:  An encoded bitstream.  Tracks contain a sequential series of
      one or more groups and are the subscribable entity with MOQT.

1.2.  Notational Conventions

   This document uses the conventions detailed in ([RFC9000],
   Section 1.3) when describing the binary encoding.

   As a quick reference, the following list provides a non-normative
   summary of the parts of RFC9000 field syntax that are used in this
   specification.

   x (L):  Indicates that x is L bits long

   x (i):  Indicates that x holds an integer value using the variable-
      length encoding as described in ([RFC9000], Section 16)

   x (..):  Indicates that x can be any length including zero bits long.
      Values in this format always end on a byte boundary.

   x (L) ...:  Indicates that x is repeated zero or more times and that
      each instance has a length of L

   This document extends the RFC9000 syntax and with the additional
   field types:

   x (b):  Indicates that x consists of a variable length integer
      encoding as described in ([RFC9000], Section 16), followed by that
      many bytes of binary data

   To reduce unnecessary use of bandwidth, variable length integers
   SHOULD be encoded using the least number of bytes possible to
   represent the required value.

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2.  Switching Tracks

   In MOQT communications, the publisher announces the availability of
   multiple encodings of a media content in different tracks, which are
   alternatives of each other and indicated so in the catalog
   [CommonCatalogFormat].  The subscriber subscribes to one of the
   tracks from an altGroup in the catalog.  During the session, the
   subscriber may switch from a currently consumed track to any other
   alternate track from the catalog due to, for example, changes in
   available bandwidth.  To do this, the subscriber can subscribe to a
   new track and unsubscribe from the old track.  Such an action is done
   by sending a SUBSCRIBE message to the relay.  An example of the
   different tracks indicated in the catalog is shown below.

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   {
       "tracks":[
           {
             "name": "hd",
             "selectionParams": {
               "width": 1920, "height": 1080,
               "bitrate": 5000000, "framerate": 30
             },
             "altGroup": 1
           },
           {
             "name": "md",
             "selectionParams": {
               "width": 720, "height": 640,
               "bitrate": 3000000, "framerate": 30
             },
             "altGroup": 1
           },
           {
             "name": "sd",
             "selectionParams": {
               "width": 192, "height": 144,
               "bitrate": 500000, "framerate": 30
             },
             "altGroup": 1
           },
           {
             "name": "audio",
             "selectionParams": {
               "codec": "opus", "samplerate": 48000,
               "channelConfig": "2", "bitrate": 32000
             }
           }
         }
       ]
   }

               Figure 1: An example of the different tracks.

2.1.  The Problem and Solution Approaches

   Relays do not have access/visibility to the catalog.  Therefore, they
   are unaware when two tracks are alternates.  An example of the
   existing SUBSCRIBE message format is shown below.

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   SUBSCRIBE Message {
     Subscribe ID (i),
     Track Alias (i),
     Track Namespace (b),
     Track Name (b),
     Filter Type (i),
     [StartGroup (i),
      StartObject (i)],
     [EndGroup (i),
      EndObject (i)],
     Number of Parameters (i),
     Subscribe Parameters (..) ...
   }

                     Figure 2: MOQT SUBSCRIBE message.

   Existing SUBSCRIBE message that the subscriber transmits to the relay
   only contains information of the current track and does not indicate
   that the client is switching to a new track for the same media
   content.  Therefore, when receiving a SUBSCRIBE message from the
   subscriber for switching to the new track, the relay may download and
   transmit both the new track and the old track of the same media
   content, which can create a bitrate spike and in turn can aggravate
   an already congested link.  Additionally, the player/client
   application on the subscriber will have to process (e.g., parse and
   decode) the same media content in overlapping times, which is a waste
   of computational power.

2.1.1.  Solution 1 (altTrackGroup)

   A new parameter altTrackGroup can be added to every SUBSCRIBE
   message. altTrackGroup is the identifier for a group of alternative
   tracks within the scope of a track namespace.  The value of the
   altTrackGroup identifier may be the same as the altGroup identifier
   used in the catalog or a different one.  An example of a SUBSCRIBE
   message that includes the identifier altTrackGroup is shown below.

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   SUBSCRIBE Message {
     Subscribe ID (i),
     Track Alias (i),
     Track Namespace (b),
     Track Name (b),
     Filter Type (i),
     [StartGroup (i),
      StartObject (i)],
     [EndGroup (i),
      EndObject (i)],
     [altTrackGroup (i)],
     Number of Parameters (i),
     Subscribe Parameters (..) ...
   }

            Figure 3: MOQT SUBSCRIBE message with altTrackGroup.

2.1.2.  Solution 2 (Switch Track Alias)

   The SUBSCRIBE message can contain an identifier Switch Track Alias
   such that the Switch Track Alias = Track Alias of the active
   subscription.  This way, this ID in the SUBSCRIBE message can
   indicate to the relay that this switching request is for an
   alternative track of the same media content of the current track and
   assists the relay in seamless switching.  An example of a SUBSCRIBE
   message that includes the identifier Switch Track Alias is shown
   below.

   SUBSCRIBE Message {
     Subscribe ID (i),
     Track Alias (i),
     Track Namespace (b),
     Track Name (b),
     Filter Type (i),
     [StartGroup (i),
      StartObject (i)],
     [EndGroup (i),
      EndObject (i)],
     [Switch Track Alias (i)],
     Number of Parameters (i),
     Subscribe Parameters (..) ...
   }

         Figure 4: MOQT SUBSCRIBE message with Switch Track Alias.

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3.  Security Considerations

   TODO: Expand this section.

4.  IANA Considerations

   TODO: Expand this section.

5.  References

5.1.  Normative References

   [MoQTransport]
              Curley, L., Pugin, K., Nandakumar, S., Vasiliev, V., and
              I. Swett, "Media over QUIC Transport", Work in Progress,
              Internet-Draft, draft-ietf-moq-transport-04, 29 May 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-moq-
              transport-04>.

   [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/rfc/rfc2119>.

   [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/rfc/rfc8174>.

5.2.  Informative References

   [CommonCatalogFormat]
              Nandakumar, S., Law, W., and M. Zanaty, "Common Catalog
              Format for moq-transport", Work in Progress, Internet-
              Draft, draft-ietf-moq-catalogformat-00, 17 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-moq-
              catalogformat-00>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/rfc/rfc9000>.

Authors' Addresses

   Zafer Gurel
   Ozyegin University
   Email: zafer.gurel@ozu.edu.tr

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   Ali Begen
   Networked Media
   Email: ali.begen@networked.media

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