H.265 Profile for WebRTC
draft-ietf-avtcore-hevc-webrtc-08

AVTCORE Working Group                                           B. Aboba
INTERNET-DRAFT                                                 P. Hancke
Category: Standards Track                          Microsoft Corporation
Expires: September 24, 2026                                       J. Qiu
                                                       Intel Corporation
                                                           23 March 2026

                        H.265 Profile for WebRTC
                 draft-ietf-avtcore-hevc-webrtc-08.txt

Abstract

   RFC 7742 defines WebRTC video processing and codec requirements,
   including guidance for endpoints supporting the VP8 and H.264 codecs,
   which are mandatory to implement.  With support for H.265 under
   development in WebRTC browsers, similar guidance is needed for
   browsers considering support for the H.265 codec, whose RTP payload
   format is defined in RFC 7798.

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 http://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 September 24, 2026.

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Copyright Notice

   Copyright (c) 2026 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2   Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
   2.  H.265 Support . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1   Parameters  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2   Feedback  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2   Packetization . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5. References . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgments   . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

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1.  Introduction

   "RTP Payload Format for High Efficiency Video Coding (HEVC)"
   [RFC7798] defines the encapsulation of H.265 [H.265] within the Real-
   time Transport Protocol (RTP) [RFC3550].  While "WebRTC Video
   Processing and Codec Requirements" [RFC7742] provides guidance for
   endpoints supporting the mandatory to implement VP8 and H.264 codecs,
   it does not cover H.265. With H.265 support shipped within browsers
   ([HEVC-Chrome] and [HEVC-WebKit]) there is a need to for an
   interoperability profile of [RFC7798] for WebRTC implementations
   choosing to support H.265.

1.1.  Terminology

   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.

1.2.  Abbreviations

    AP       Aggregation Packet
    BLA      Broken Link Access
    CRA      Clean Random Access
    FU       Fragmentation Unit
    IDR      Instantaneous Decoding Refresh
    IRAP     Intra Random Access Point
    MANE     Media-Aware Network Element
    MRMT     Multiple RTP streams on Multiple media Transports
    MRST     Multiple RTP streams on a Single media Transport
    NAL      Network Abstraction Layer
    NALU     Network Abstraction Layer Unit
    PACI     PAyload Content Information
    PPS      Picture Parameter Set
    SEI      Supplemental Enhancement Information
    SFM      Selectively Forwarding Middlebox
    SPS      Sequence Parameter Set
    SRST     Single RTP stream on a Single media Transport
    TID      Temporal Identifier
    TSCI     Temporal Scalability Control Information
    VCL      Video Coding Layer
    VPS      Video Parameter Set

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2.  H.265 Support

   Support for the H.265 video codec is OPTIONAL for WebRTC browsers and
   non-browsers.  Implementations supporting H.265 that conform to this
   specification MUST support receiving H.265 and MAY support sending
   H.265.

   For the H.265 [H.265] codec, endpoints MUST support the payload
   formats defined in [RFC7798]. In addition, they MUST support Main
   Profile Level 3.1 (level-id=93) and SHOULD support Main Profile Level
   4 (level-id=120).

   [RFC7798] Section 4.5 defines how TSCI is communicated using PACI
   Extensions defined in [RFC7798] Section 4.4.4.2.  A WebRTC
   implementation that has negotiated use of RTP header extensions
   containing TSCI information (such as the Dependency Descriptor [DD])
   SHOULD NOT send TSCI information within the PACI.  If TSCI
   information is being received in an RTP header extension,
   implementations MUST ignore TSCI information contained in the PACI.

   [RFC7798] Section 4.4.2 describes how APs are carried within RTP
   payloads:

      "An AP consists of a payload header (denoted as PayloadHdr)
      followed by two or more aggregation units... The value of TID MUST
      be the lowest value of TID of all the aggregated NAL units.

         Informative note: All VCL NAL units in an AP have the same TID
         value since they belong to the same access unit.  However, an
         AP may contain non-VCL NAL units for which the TID value in the
         NAL unit header may be different than the TID value of the VCL
         NAL units in the same AP."

   Within an RTP payload, VCL NAL units MUST NOT be aggregated with non-
   VCL NAL units with a lower TID value.  Instead the non-VCL NAL units
   with a lower TID value MUST be packetized within a distinct RTP
   packet.  This ensures that a MANE or SFM can forward VCL and non-VCL
   NAL units to the correct set of participants.

2.1.  Parameters

   Implementations of the H.265 codec have utilized a wide variety of
   optional parameters. The H.265 "media format" includes the following
   fmtp parameters: profile-id, tier-flag, and tx-mode.

   To improve interoperability, the following parameter settings are
   specified:

   level-id: Implementations SHOULD include this parameter within SDP
   and MUST interpret it when receiving it. If no level-id is present, a
   value of 93 (i.e., Level 3.1) MUST be inferred.

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   On a sendrecv m-line, the offered level-id represents the maximum
   that can be both sent and received; on a sendonly m-line, the 
   offered level-id represents the maximum that can be sent; on a
   recvonly m-line, the offered level-id represents the maximum that
   can be received.

   As noted in [RFC7798] Section 5, the "highest level indicated by the
   answer is either equal to or lower than that in the offer."

   tx-mode: Implementations SHOULD include this parameter within SDP.
   If no tx-mode parameter is present, a value of "SRST" MUST be
   inferred.  Implementations MUST support "SRST"; support for "MRST"
   and "MRMT" are OPTIONAL. Implementations that do not support "MRST"
   or "MRMT" MUST NOT include these tx-mode values in SDP.

   sprop-sps, sprop-pps, sprop-vps, sprop-sei: H.265 allows sequence and
   picture information to be sent both in-band and out-of-band.  WebRTC
   implementations MUST signal this information in-band.  This means
   that WebRTC implementations MUST NOT include these parameters in the
   SDP they generate, and SHOULD silently ignore these parameters if
   they are received. An IDR/CRA/BLA sent MUST always be preceded by the
   relevant parameter sets sent in a packet (not necessarily a separate
   packet) with the same RTP timestamp as the IDR/CRA/BLA.

   When the use of the video orientation (CVO) RTP header extension is
   not signaled as part of the SDP, H.265 implementations MAY send and
   SHOULD support proper interpretation of Display Orientation SEI
   messages.

   [RFC7798] Section 8.3 specifies the use of the Reference Picture
   Selection Indication (RPSI) in H.265. Implementations MUST use the
   RPSI feedback message only as a reference picture selection request,
   and MUST NOT use it as positive acknowledgement. Receivers that
   detect that H.265 encoder-decoder synchronization has been lost
   SHOULD generate an RPSI feedback message if support for RPSI has
   been negotiated, unless the receiver has knowledge that the sender
   does not support RPSI. Such knowledge can be established during
   capability exchange or through previously sent RPSI requests that
   were not replied to by the sender through the use of a non-IRAP
   picture. An RTP packet-stream sender that receives an RPSI message
   MUST act on that message, and SHOULD change the reference picture.

   Unless otherwise signaled, WebRTC implementations that support H.265
   MUST encode and decode pixels with an implied 1:1 (square) aspect
   ratio.

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2.2.  Feedback

   [RFC7798] Section 8.3 specifies the use of the Reference Picture
   Selection Indication (RPSI) in H.265. Implementations MUST use the
   RPSI feedback message only as a reference picture selection request,
   and MUST NOT use it as positive acknowledgement. Receivers that
   detect that H.265 encoder-decoder synchronization has been lost
   SHOULD generate an RPSI feedback message if support for RPSI has been
   negotiated, unless the receiver has knowledge that the sender does
   not support RPSI. Such knowledge can be established during capability
   exchange or through previously sent RPSI requests that were not
   replied to by the sender through the use of a non-IRAP picture.  An
   RTP packet-stream sender that receives an RPSI message MUST act on
   that message, and SHOULD change the reference picture.

2.3.  Packetization

   [RFC7798] Section 5 specifiies the packetization rules for H.265.
   In addition to these rules, Prefix SEI NAL units in an IRAP picture
   MUST NOT be packetized before any VPS, SPS and PPS NAL units.
   This ensures they will be assembled as part of IRAP picture without
   being dropped.

3.  Security Considerations

   This document is subject to the security considerations described in
   Section 7 of [RFC7742].

   In addition to those security considerations, H.265 implementers are
   advised to take note of the "Security Considerations" Section 9 of
   [RFC7798], including requirements pertaining to SEI messages.

4.  IANA Considerations

   This document does not require actions by IANA.

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5.  References

5.1.  Normative References

[DD]           Alliance for Open Media (AoMedia), "Dependency Descriptor
               RTP Header Extension",
               https://aomediacodec.github.io/av1-rtp-spec/#dependency-
               descriptor-rtp-header-extension, retrieved September 19,
               2023.

[H.265]        ITU-T, "High efficiency video coding", ITU-T
               Recommendation H.265, April 2013.

[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>.

[RFC3550]      Schulzrinne, H., Casner, S., Frederick, R., and V.
               Jacobson, "RTP: A Transport Protocol for Real-Time
               Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
               July 2003, <https://www.rfc-editor.org/info/rfc3550>.

[RFC7742]      Roach, A. B., "WebRTC Video Processing and Codec
               Requirements", RFC 7742, DOI 10.17487/RFC7742, March
               2016, <https://www.rfc-editor.org/info/rfc7742>.

[RFC7798]      Wang, Y.K., Sanchez, Y., Schierl, T., Wenger, S. and M.
               M. Hannuksela, "RTP Payload Format for High Efficiency
               Video Coding (HEVC)", RFC 7798, DOI 10.17487/RFC7798,
               March 2016, <https://www.rfc-editor.org/info/rfc7798>.

[RFC8174]      Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
               2119 Key Words", RFC 8174, DOI 10.17487/RFC8174, May
               2017, <https://www.rfc-editor.org/info/rfc8174>.

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5.2.  Informative References

[HEVC-Chrome]  "H265 (HEVC) codec support in WebRTC",
               https://chromestatus.com/feature/5153479456456704,
               retrieved March 18, 2026.

[HEVC-WebKit]  "WebKit Features in Safari 18.0",
               https://webkit.org/blog/15865/webkit-features-in-
               safari-18-0/, retrieved March 18, 2026.

Acknowledgments

   We would like to thank Stephan Wenger, Jonathan Lennox, Harald
   Alvestrand, Philip Eliasson and Henrik Bostrom for their discussions
   of this problem space.

   Bernard Aboba who was the driving force behind this specification
   passed away on February 1st, 2025.

Authors' Addresses

   Bernard Aboba
   Microsoft Corporation

   Philipp Hancke
   Email: philipp.hancke@googlemail.com

   Jianlin Qiu
   Intel Corporation

   Email: jianlin.qiu@intel.com

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