RFC 9751

Closing the RTP Payload Format Media Types Registry

📅 published March 2025, from ietf

Closing the RTP Payload Format Media Types Registry ✨

Okay bestie, this is RFC 9751 🎀, and it's a whole vibe. Here's the title block tea 🫖:

Author: M. Westerlund at Ericsson 🫶 Category: Standards Track 👑 Date: March 2025 📅 Stream: Internet Engineering Task Force (IETF) 🌸 ISSN: 2070-1721 ✨ Updates: RFC 8088 (the "How to Write an RTP Payload Format" one) 🧚 Obsoletes: this header doesn't list anything it obsoletes 🙈

Abstract 💜

Okay so the working group process and the RTP payload format authors have sometimes forgotten to get media types registered in the IANA "RTP Payload Format Media Types" registry, even though RFC 8088 recommends it 😭. To make life easier and rely only on the "Media Types" registry, this doc closes the RTP payload-specific registry 💅. It also updates the instruction in RFC 8088 so it matches 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 give feedback on it can be found at https://www.rfc-editor.org/info/rfc9751.

Copyright (c) 2025 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) as they stand on the date this document is published. Please read these carefully, because they explain your rights and restrictions with respect to this document. Code Components pulled out of this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Revised BSD License 🫶.

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 🦋

Okay so, sometimes authors writing new Real-time Transport Protocol (RTP) payload formats just forgot to say their media type should go in the "RTP Payload Format Media Types" registry [RTP-FORMATS], even though [RFC8088] recommends it. 🙈 In practice this has zero real impact, because that registry isn't used for anything except tracking which media types have RTP payload formats, and that can be done some other way 💁‍♀️.

Media types are required to be registered in the "Media Types" registry [MEDIA-TYPES] so that they can identify the format in various signalling usages, avoid collisions, and reference the defining specifications. That's the important one 👑.

To fix this mess, this document:

  • updates the "RTP Payload Format Media Types" registry to include the 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 kind of unclear 🕵️‍♀️. The registry cites [RFC4855] as the source of instructions for maintaining it. However, when people looked at RFC 4855, they found no text defining the registry's purpose or operational rules. Further attempts to trace how the registry was created turned up no references to its establishment. It's likely the registry was created from email correspondence or at the request of an Area Director. So, there's no known specification for this registry that needs updating when it gets closed 💀.

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]) says RTP payload formats shall be registered in the "RTP Payload Format Media Types" registry. The paragraph below is updated as shown, which removes the need for media types to be registered there. Note that this update does not affect 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 also 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 note to the registry:

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, because 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

That's the whole RFC, bestie!! 🌈✨ Thanks for reading, and go be iconic 👑💅

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