



Internet Engineering Task Force (IETF)                     M. Westerlund
Request for Comments: 9751                                      Ericsson
Updates: 8088                                                 March 2025
Category: Standards Track                                               
ISSN: 2070-1721


          Closing the RTP Payload Format Media Types Registry

Abstract

   The working group process and the authors of RTP payload formats have
   sometimes failed to ensure that the media types are registered in the
   IANA "RTP Payload Format Media Types" registry as recommended by RFC
   8088.  To simplify the process and rely only on the "Media Types"
   registry, this document closes the RTP payload- specific registry.
   In addition, it updates the instruction in RFC 8088 to reflect this
   change.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9751.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction
   2.  Update to How to Write an RTP Payload Format
   3.  IANA Considerations
   4.  Security Considerations
   5.  References
     5.1.  Normative References
     5.2.  Informative References
   Acknowledgments
   Author's Address

1.  Introduction

   Sometimes, authors defining new Real-time Transport Protocol (RTP)
   payload formats forgot to specify registration of the format's media
   type in the "RTP Payload Format Media Types" registry [RTP-FORMATS]
   as recommended by [RFC8088].  In practice, this has no real impact.
   This registry is not used for any purpose other than to track which
   media types actually have RTP payload formats, which can be done
   through other means.

   It is required that media types be registered in the "Media Types"
   registry [MEDIA-TYPES] to identify the format in various signalling
   usages, avoid collisions, and reference the defining specifications.

   To resolve this situation, this document:

   *  updates the "RTP Payload Format Media Types" registry to include
      known RTP payload formats at the time of writing,

   *  closes the "RTP Payload Format Media Types" registry to future
      registrations and lists this RFC as a reference, and

   *  removes from [RFC8088] the instruction to register RTP payload
      formats in the "RTP Payload Format Media Types" registry.

   The origins of the "RTP Payload Format Media Types" registry, as
   referenced in [RTP-FORMATS], are unclear.  The registry cites
   [RFC4855] as providing the instructions for its maintenance.
   However, upon reviewing RFC 4855, no text has been found that defines
   the registry's purpose and operational rules.  Further attempts to
   trace the registry's creation have failed to uncover any references
   to its establishment.  It is likely that the registry was created
   based on email correspondence or at the request of an Area Director.
   Consequently, there is no known specification for this registry that
   requires updating upon its closure.

2.  Update to How to Write an RTP Payload Format

   The IANA Considerations section of "How to write an RTP Payload
   Format" (Section 7.4 of [RFC8088]) mandates that RTP payload formats
   shall be registered in the "RTP Payload Format Media Types" registry.
   The following paragraph is updated as shown below, thus removing the
   need for media types to be registered in the "RTP Payload Format
   Media Types" registry.  Note that this update does not impact the
   rest of RFC 8088's status as an Informational RFC.

   OLD:

   |  Since all RTP payload formats contain a media type specification,
   |  they also need an IANA Considerations section.  The media type
   |  name must be registered, and this is done by requesting that IANA
   |  register that media name.  When that registration request is
   |  written, it shall also be requested that the media type is
   |  included under the "RTP Payload Format media types" sub-registry
   |  of the RTP registry (http://www.iana.org/assignments/rtp-
   |  parameters).

   NEW:

   |  Since all RTP payload formats contain a media type specification,
   |  they also need an IANA Considerations section.  The media type
   |  name must be registered, and this is done by requesting that IANA
   |  register that media name in the "Media Types" registry
   |  (https://www.iana.org/assignments/media-types/).

3.  IANA Considerations

   IANA has added the following RTP payload types to the "RTP Payload
   Format Media Types" registry [RTP-FORMATS].

   +=============+==========+===========+==========+==================+
   | Media Type  | Subtype  | Clock     | Channels | Reference        |
   |             |          | Rate (Hz) | (audio)  |                  |
   +=============+==========+===========+==========+==================+
   | application | flexfec  |           |          | RFC 8627         |
   +-------------+----------+-----------+----------+------------------+
   | audio       | EVRCNW   | 16000     |          | RFC 6884         |
   +-------------+----------+-----------+----------+------------------+
   | audio       | EVRCNW0  | 16000     |          | RFC 6884         |
   +-------------+----------+-----------+----------+------------------+
   | audio       | EVRCNW1  | 16000     |          | RFC 6884         |
   +-------------+----------+-----------+----------+------------------+
   | audio       | aptx     |           |          | RFC 7310         |
   +-------------+----------+-----------+----------+------------------+
   | audio       | opus     | 48000     |          | RFC 7587         |
   +-------------+----------+-----------+----------+------------------+
   | audio       | G711-0   |           |          | RFC 7650         |
   +-------------+----------+-----------+----------+------------------+
   | audio       | flexfec  |           |          | RFC 8627         |
   +-------------+----------+-----------+----------+------------------+
   | text        | flexfec  |           |          | RFC 8627         |
   +-------------+----------+-----------+----------+------------------+
   | text        | ttml+xml |           |          | RFC 8759         |
   +-------------+----------+-----------+----------+------------------+
   | video       | VP8      | 90000     |          | RFC 7741         |
   +-------------+----------+-----------+----------+------------------+
   | video       | AV1      | 90000     |          | [AV1-Media-Type] |
   +-------------+----------+-----------+----------+------------------+
   | video       | HEVC     | 90000     |          | RFC 7798         |
   +-------------+----------+-----------+----------+------------------+
   | video       | smpte291 |           |          | RFC 8331         |
   +-------------+----------+-----------+----------+------------------+
   | video       | VVC      | 90000     |          | RFC 9328         |
   +-------------+----------+-----------+----------+------------------+
   | video       | EVC      | 90000     |          | RFC 9584         |
   +-------------+----------+-----------+----------+------------------+
   | video       | flexfec  |           |          | RFC 8627         |
   +-------------+----------+-----------+----------+------------------+

       Table 1: Payload Types Added to the RTP Payload Format Media
                              Types Registry

   IANA has updated the following entries in the "RTP Payload Format
   Media Types" registry [RTP-FORMATS].

    +============+===========+=================+==========+===========+
    | Media Type | Subtype   | Clock Rate (Hz) | Channels | Reference |
    |            |           |                 | (audio)  |           |
    +============+===========+=================+==========+===========+
    | audio      | MP4A-LATM |                 |          | RFC 6416  |
    +------------+-----------+-----------------+----------+-----------+
    | video      | MP4V-ES   | 90000           |          | RFC 6416  |
    +------------+-----------+-----------------+----------+-----------+

         Table 2: Payload Types Updated in RTP Payload Format Media
                               Types Registry

   IANA has also closed the "RTP Payload Format Media Types" registry
   [RTP-FORMATS] to any further registrations.  IANA added the following
   to the registry note:

   NEW:

   |  This registry has been closed; it was considered redundant because
   |  all RTP payload formats are part of the [Media Types registry]
   |  (https://www.iana.org/assignments/media-types).  See RFC 9751 for
   |  further details.

   In addition, IANA updated the note in the "RTP Payload Format Media
   Types" registry [RTP-FORMATS] as follows:

   OLD:

   |  Registration procedures and a registration template can be found
   |  in [RFC4855].

   NEW:

   |  It was previously stated that registration procedures and a
   |  registration template can be found in [RFC4855].  As documented in
   |  RFC 9751, this is not the case.

4.  Security Considerations

   This document has no security considerations as it defines an
   administrative rule change.

5.  References

5.1.  Normative References

   [AV1-Media-Type]
              IANA, "video/AV1",
              <https://www.iana.org/assignments/media-types/video/AV1>.

   [MEDIA-TYPES]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types>.

   [RFC8088]  Westerlund, M., "How to Write an RTP Payload Format",
              RFC 8088, DOI 10.17487/RFC8088, May 2017,
              <https://www.rfc-editor.org/info/rfc8088>.

   [RTP-FORMATS]
              IANA, "RTP Payload Format Media Types",
              <https://www.iana.org/assignments/rtp-parameters>.

5.2.  Informative References

   [RFC4855]  Casner, S., "Media Type Registration of RTP Payload
              Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
              <https://www.rfc-editor.org/info/rfc4855>.

Acknowledgments

   The author thanks Jonathan Lennox, Zaheduzzaman Sarker, Bernard
   Aboba, Elwyn Davies, Wes Hardaker, Gunter Van de Velde, Éric Vyncke,
   Mahesh Jethanandani, and Hyunsik Yang for their reviews and editorial
   fixes.

Author's Address

   Magnus Westerlund
   Ericsson
   Email: magnus.westerlund@ericsson.com
