rfc9628.original   rfc9628.txt 
AVTCore Working Group J. Uberti Internet Engineering Task Force (IETF) J. Uberti
Internet-Draft S. Holmer Request for Comments: 9628 S. Holmer
Intended status: Standards Track M. Flodman Category: Standards Track M. Flodman
Expires: 12 December 2021 D. Hong ISSN: 2070-1721 D. Hong
Google Google
J. Lennox J. Lennox
8x8 / Jitsi 8x8 / Jitsi
10 June 2021 August 2024
RTP Payload Format for VP9 Video RTP Payload Format for VP9 Video
draft-ietf-payload-vp9-16
Abstract Abstract
This specification describes an RTP payload format for the VP9 video This specification describes an RTP payload format for the VP9 video
codec. The payload format has wide applicability, as it supports codec. The payload format has wide applicability as it supports
applications from low bit-rate peer-to-peer usage, to high bit-rate applications from low bitrate peer-to-peer usage to high bitrate
video conferences. It includes provisions for temporal and spatial video conferences. It includes provisions for temporal and spatial
scalability. scalability.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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 This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 12 December 2021. 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/rfc9628.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
2. Conventions, Definitions and Acronyms . . . . . . . . . . . . 3 2. Conventions
3. Media Format Description . . . . . . . . . . . . . . . . . . 3 3. Media Format Description
4. Payload Format . . . . . . . . . . . . . . . . . . . . . . . 5 4. Payload Format
4.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . 5 4.1. RTP Header Usage
4.2. VP9 Payload Descriptor . . . . . . . . . . . . . . . . . 6 4.2. VP9 Payload Descriptor
4.2.1. Scalability Structure (SS): . . . . . . . . . . . . . 11 4.2.1. Scalability Structure (SS)
4.3. Frame Fragmentation . . . . . . . . . . . . . . . . . . . 13 4.3. Frame Fragmentation
4.4. Scalable encoding considerations . . . . . . . . . . . . 13 4.4. Scalable Encoding Considerations
4.5. Examples of VP9 RTP Stream . . . . . . . . . . . . . . . 13 4.5. Examples of VP9 RTP Stream
4.5.1. Reference picture use for scalable structure . . . . 14 4.5.1. Reference Picture Use for Scalable Structure
5. Feedback Messages and Header Extensions . . . . . . . . . . . 14 5. Feedback Messages and Header Extensions
5.1. Reference Picture Selection Indication (RPSI) . . . . . . 15 5.1. Reference Picture Selection Indication (RPSI)
5.2. Full Intra Request (FIR) . . . . . . . . . . . . . . . . 15 5.2. Full Intra Request (FIR)
5.3. Layer Refresh Request (LRR) . . . . . . . . . . . . . . . 15 5.3. Layer Refresh Request (LRR)
6. Payload Format Parameters . . . . . . . . . . . . . . . . . . 16 6. Payload Format Parameters
6.1. SDP Parameters . . . . . . . . . . . . . . . . . . . . . 18 6.1. SDP Parameters
6.1.1. Mapping of Media Subtype Parameters to SDP . . . . . 18 6.1.1. Mapping of Media Subtype Parameters to SDP
6.1.2. Offer/Answer Considerations . . . . . . . . . . . . . 19 6.1.2. Offer/Answer Considerations
7. Media Type Definition . . . . . . . . . . . . . . . . . . . . 19 7. Media Type Definition
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 8. Security Considerations
9. Congestion Control . . . . . . . . . . . . . . . . . . . . . 21 9. Congestion Control
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 10. IANA Considerations
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 11. References
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 11.1. Normative References
12.1. Normative References . . . . . . . . . . . . . . . . . . 22 11.2. Informative References
12.2. Informative References . . . . . . . . . . . . . . . . . 23 Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses
1. Introduction 1. Introduction
This specification describes an RTP [RFC3550] payload specification This document describes an RTP [RFC3550] payload specification
applicable to the transmission of video streams encoded using the VP9 applicable to the transmission of video streams encoded using the VP9
video codec [VP9-BITSTREAM]. The format described in this document video codec [VP9-BITSTREAM]. The format described in this document
can be used both in peer-to-peer and video conferencing applications. can be used both in peer-to-peer and video conferencing applications.
The VP9 video codec was developed by Google, and is the successor to The VP9 video codec was developed by Google and is the successor to
its earlier VP8 [RFC6386] codec. Above the compression improvements its earlier VP8 [RFC6386] codec. Above the compression improvements
and other general enhancements above VP8, VP9 is also designed in a and other general enhancements to VP8, VP9 is also designed in a way
way that allows spatially-scalable video encoding. that allows spatially scalable video encoding.
2. Conventions, Definitions and Acronyms 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Media Format Description 3. Media Format Description
The VP9 codec can maintain up to eight reference frames, of which up The VP9 codec can maintain up to eight reference frames, of which up
to three can be referenced by any new frame. to three can be referenced by any new frame.
VP9 also allows a frame to use another frame of a different VP9 also allows a frame to use another frame of a different
resolution as a reference frame. (Specifically, a frame may use any resolution as a reference frame. (Specifically, a frame may use any
references whose width and height are between 1/16th that of the references whose width and height are between 1/16th that of the
current frame and twice that of the current frame, inclusive.) This current frame and twice that of the current frame, inclusive.) This
allows internal resolution changes without requiring the use of key allows internal resolution changes without requiring the use of
frames. keyframes.
These features together enable an encoder to implement various forms These features together enable an encoder to implement various forms
of coarse-grained scalability, including temporal, spatial and of coarse-grained scalability, including temporal, spatial, and
quality scalability modes, as well as combinations of these, without quality scalability modes, as well as combinations of these, without
the need for explicit scalable coding tools. the need for explicit scalable coding tools.
Temporal layers define different frame rates of video; spatial and Temporal layers define different frame rates of video; spatial and
quality layers define different and possibly dependent quality layers define different and possibly dependent
representations of a single input frame. Spatial layers allow a representations of a single input frame. Spatial layers allow a
frame to be encoded at different resolutions, whereas quality layers frame to be encoded at different resolutions, whereas quality layers
allow a frame to be encoded at the same resolution but at different allow a frame to be encoded at the same resolution but at different
qualities (and thus with different amounts of coding error). VP9 qualities (and, thus, with different amounts of coding error). VP9
supports quality layers as spatial layers without any resolution supports quality layers as spatial layers without any resolution
changes; hereinafter, the term "spatial layer" is used to represent changes; hereinafter, the term "spatial layer" is used to represent
both spatial and quality layers. both spatial and quality layers.
This payload format specification defines how such temporal and This payload format specification defines how such temporal and
spatial scalability layers can be described and communicated. spatial scalability layers can be described and communicated.
Temporal and spatial scalability layers are associated with non- Temporal and spatial scalability layers are associated with non-
negative integer IDs. The lowest layer of either type has an ID of negative integer IDs. The lowest layer of either type has an ID of 0
0, and is sometimes referred to as the "base" temporal or spatial and is sometimes referred to as the "base" temporal or spatial layer.
layer.
Layers are designed, and MUST be encoded, such that if any layer, and Layers are designed, and MUST be encoded, such that if any layer, and
all higher layers, are removed from the bitstream along either the all higher layers, are removed from the bitstream along either the
spatial or temporal dimension, the remaining bitstream is still spatial or temporal dimension, the remaining bitstream is still
correctly decodable. correctly decodable.
For terminology, this document uses the term "frame" to refer to a For terminology, this document uses the term "frame" to refer to a
single encoded VP9 frame for a particular resolution/quality, and single encoded VP9 frame for a particular resolution and/or quality,
"picture" to refer to all the representations (frames) at a single and "picture" to refer to all the representations (frames) at a
instant in time. A picture thus consists of one or more frames, single instant in time. Thus, a picture consists of one or more
encoding different spatial layers. frames, encoding different spatial layers.
Within a picture, a frame with spatial layer ID equal to SID, where Within a picture, a frame with spatial-layer ID equal to S, where S >
SID > 0, can depend on a frame of the same picture with a lower 0, can depend on a frame of the same picture with a lower spatial-
spatial layer ID. This "inter-layer" dependency can result in layer ID. This "inter-layer" dependency can result in additional
additional coding gain compared to the case where only traditional coding gain compared to the case where only "inter-picture"
"inter-picture" dependency is used, where a frame depends on dependency is used, where a frame depends on a previously coded frame
previously coded frame in time. For simplicity, this payload format in time. For simplicity, this payload format assumes that, within a
assumes that, within a picture and if inter-layer dependency is used, picture and if inter-layer dependency is used, a spatial-layer S
a spatial layer SID frame can depend only on the immediately previous frame can depend only on the immediately previous spatial-layer S-1
spatial layer SID-1 frame, when S > 0. Additionally, if inter- frame, when S > 0. Additionally, if inter-picture dependency is
picture dependency is used, a spatial layer SID frame is assumed to used, a spatial-layer S frame is assumed to only depend on a
only depend on a previously coded spatial layer SID frame. previously coded spatial-layer S frame.
Given above simplifications for inter-layer and inter-picture Given the above simplifications for inter-layer and inter-picture
dependencies, a flag (the D bit described below) is used to indicate dependencies, a flag (the D bit described below) is used to indicate
whether a spatial layer SID frame depends on the spatial layer SID-1 whether a spatial-layer SID frame depends on the spatial-layer SID-1
frame. Given the D bit, a receiver only needs to additionally know frame. Given the D bit, a receiver only needs to additionally know
the inter-picture dependency structure for a given spatial layer the inter-picture dependency structure for a given spatial-layer
frame in order to determine its decodability. Two modes of frame in order to determine its decodability. Two modes of
describing the inter-picture dependency structure are possible: describing the inter-picture dependency structure are possible:
"flexible mode" and "non-flexible mode". An encoder can only switch "flexible mode" and "non-flexible mode". An encoder can only switch
between the two on the first packet of a key frame with temporal between the two on the first packet of a keyframe with a temporal-
layer ID equal to 0. layer ID equal to 0.
In flexible mode, each packet can contain up to 3 reference indices, In flexible mode, each packet can contain up to three reference
which identify all frames referenced by the frame transmitted in the indices, which identify all frames referenced by the frame
current packet for inter-picture prediction. This (along with the D transmitted in the current packet for inter-picture prediction. This
bit) enables a receiver to identify if a frame is decodable or not (along with the D bit) enables a receiver to identify if a frame is
and helps it understand the temporal layer structure. Since this is decodable or not and helps it understand the temporal-layer
signaled in each packet it makes it possible to have very flexible structure. Since this is signaled in each packet, it makes it
temporal layer hierarchies, and scalability structures which are possible to have very flexible temporal-layer hierarchies and
changing dynamically. scalability structures, which are changing dynamically.
In non-flexible mode, frames are encoded using a fixed, recurring In non-flexible mode, frames are encoded using a fixed, recurring
pattern of dependencies; the set of pictures that recur in this pattern of dependencies; the set of pictures that recur in this
pattern is known as a Picture Group (PG). In this mode, the inter- pattern is known as a "Picture Group" (or "PG"). In this mode, the
picture dependencies (the reference indices) of the Picture Group inter-picture dependencies (the reference indices) of the PG MUST be
MUST be pre-specified as part of the scalability structure (SS) data. pre-specified as part of the Scalability Structure (SS) data. Each
Each packet has an index to refer to one of the described pictures in packet has an index to refer to one of the described pictures in the
the PG, from which the pictures referenced by the picture transmitted PG from which the pictures referenced by the picture transmitted in
in the current packet for inter-picture prediction can be identified. the current packet for inter-picture prediction can be identified.
(Note: A "Picture Group", as used in this document, is not the same
thing as the term "Group of Pictures" as it is traditionally used in
video coding, i.e. to mean an independently-decoadable run of
pictures beginning with a keyframe.)
The SS data can also be used to specify the resolution of each | Note: A "Picture Group" or "PG", as used in this document, is
spatial layer present in the VP9 stream for both flexible and non- | not the same thing as the term "Group of Pictures" as it is
flexible modes. | commonly used in video coding, i.e., to mean an independently
| decodable run of pictures beginning with a keyframe.
|
| The SS data can also be used to specify the resolution of each
| spatial layer present in the VP9 stream for both flexible and
| non-flexible modes.
4. Payload Format 4. Payload Format
This section describes how the encoded VP9 bitstream is encapsulated This section describes how the encoded VP9 bitstream is encapsulated
in RTP. To handle network losses usage of RTP/AVPF [RFC4585] is in RTP. To handle network losses, usage of RTP/AVPF [RFC4585] is
RECOMMENDED. All integer fields in the specifications are encoded as RECOMMENDED. All integer fields in this specification are encoded as
unsigned integers in network octet order. unsigned integers in network octet order.
4.1. RTP Header Usage 4.1. RTP Header Usage
The general RTP payload format for VP9 is depicted below. The general RTP payload format for VP9 is depicted below.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | sequence number | |V=2|P|X| CC |M| PT | sequence number |
skipping to change at page 6, line 4 skipping to change at line 231
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : | | : |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
+ | + |
: VP9 payload : : VP9 payload :
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : OPTIONAL RTP padding | | : OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
The VP9 payload descriptor will be described in Section 4.2; the VP9 Figure 1: General RTP Payload Format for VP
payload is described in [VP9-BITSTREAM]. OPTIONAL RTP padding MUST
NOT be included unless the P bit is set.
Marker bit (M): MUST be set to 1 for the final packet of the highest See Section 4.2 for more information on the VP9 payload descriptor;
spatial layer frame (the final packet of the picture), and 0 the VP9 payload is described in [VP9-BITSTREAM]. OPTIONAL RTP
otherwise. Unless spatial scalability is in use for this picture, padding MUST NOT be included unless the P bit is set.
this will have the same value as the E bit described below. Note
this bit MUST be set to 1 for the target spatial layer frame if a Marker bit (M): This bit MUST be set to 1 for the final packet of
stream is being rewritten to remove higher spatial layers. the highest spatial-layer frame (the final packet of the picture);
otherwise, it MUST be set to 0. Unless spatial scalability is in
use for this picture, this bit will have the same value as the E
bit described in Section 4.2. Note this bit MUST be set to 1 for
the target spatial-layer frame if a stream is being rewritten to
remove higher spatial layers.
Payload Type (PT): In line with the policy in Section 3 of Payload Type (PT): In line with the policy in Section 3 of
[RFC3551], applications using the VP9 RTP payload profile MUST [RFC3551], applications using the VP9 RTP payload profile MUST
assign a dynamic payload type number to be used in each RTP assign a dynamic payload type number to be used in each RTP
session and provide a mechanism to indicate the mapping. See session and provide a mechanism to indicate the mapping. See
Section 6.1 for the mechanism to be used with the Session Section 6.1 for the mechanism to be used with the Session
Description Protocol (SDP) [RFC8866]. Description Protocol (SDP) [RFC8866].
Timestamp: The RTP timestamp [RFC3550] indicates the time when the Timestamp: The RTP timestamp [RFC3550] indicates the time when the
input frame was sampled, at a clock rate of 90 kHz. If the input input frame was sampled, at a clock rate of 90 kHz. If the input
picture is encoded with multiple layer frames, all of the frames picture is encoded with multiple-layer frames, all of the frames
of the picture MUST have the same timestamp. of the picture MUST have the same timestamp.
If a frame has the VP9 show_frame field set to 0 (i.e., it is If a frame has the VP9 show_frame field set to 0 (i.e., it is
meant only to populate a reference buffer, without being output) meant only to populate a reference buffer without being output),
its timestamp MAY alternatively be set to be the same as the its timestamp MAY alternatively be set to be the same as the
subsequent frame with show_frame equal to 1. (This will be subsequent frame with show_frame equal to 1. (This will be
convenient for playing out pre-encoded content packaged with VP9 convenient for playing out pre-encoded content packaged with VP9
"superframes", which typically bundle show_frame==0 frames with a "superframes", which typically bundle show_frame==0 frames with a
subsequent show_frame==1 frame.) Every frame with show_frame==1, subsequent show_frame==1 frame.) Every frame with show_frame==1,
however, MUST have a unique timestamp modulo the 2^32 wrap of the however, MUST have a unique timestamp modulo the 2^32 wrap of the
field. field.
The remaining RTP Fixed Header Fields (V, P, X, CC, sequence number, The remaining RTP Fixed Header Fields (V, P, X, CC, sequence number,
SSRC and CSRC identifiers) are used as specified in Section 5.1 of SSRC, and CSRC identifiers) are used as specified in Section 5.1 of
[RFC3550]. [RFC3550].
4.2. VP9 Payload Descriptor 4.2. VP9 Payload Descriptor
In flexible mode (with the F bit below set to 1), the first octets In flexible mode (with the F bit below set to 1), the first octets
after the RTP header are the VP9 payload descriptor, with the after the RTP header are the VP9 payload descriptor, with the
following structure. following structure.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
skipping to change at page 7, line 21 skipping to change at line 294
M: | EXTENDED PID | (RECOMMENDED) M: | EXTENDED PID | (RECOMMENDED)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
L: | TID |U| SID |D| (Conditionally RECOMMENDED) L: | TID |U| SID |D| (Conditionally RECOMMENDED)
+-+-+-+-+-+-+-+-+ -\ +-+-+-+-+-+-+-+-+ -\
P,F: | P_DIFF |N| (Conditionally REQUIRED) - up to 3 times P,F: | P_DIFF |N| (Conditionally REQUIRED) - up to 3 times
+-+-+-+-+-+-+-+-+ -/ +-+-+-+-+-+-+-+-+ -/
V: | SS | V: | SS |
| .. | | .. |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 2 Figure 2: Flexible Mode Format for VP9 Payload Descriptor
In non-flexible mode (with the F bit below set to 0), the first In non-flexible mode (with the F bit below set to 0), the first
octets after the RTP header are the VP9 payload descriptor, with the octets after the RTP header are the VP9 payload descriptor, with the
following structure. following structure.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|I|P|L|F|B|E|V|Z| (REQUIRED) |I|P|L|F|B|E|V|Z| (REQUIRED)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
I: |M| PICTURE ID | (RECOMMENDED) I: |M| PICTURE ID | (RECOMMENDED)
skipping to change at page 7, line 43 skipping to change at line 316
M: | EXTENDED PID | (RECOMMENDED) M: | EXTENDED PID | (RECOMMENDED)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
L: | TID |U| SID |D| (Conditionally RECOMMENDED) L: | TID |U| SID |D| (Conditionally RECOMMENDED)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| TL0PICIDX | (Conditionally REQUIRED) | TL0PICIDX | (Conditionally REQUIRED)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
V: | SS | V: | SS |
| .. | | .. |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 3 Figure 3: Non-flexible Mode Format for VP9 Payload Descriptor
I: Picture ID (PID) present. When set to one, the OPTIONAL PID MUST I: Picture ID (PID) present. When set to 1, the OPTIONAL PID MUST
be present after the mandatory first octet and specified as below. be present after the mandatory first octet and specified as below.
Otherwise, PID MUST NOT be present. If the V bit was set in the Otherwise, PID MUST NOT be present. If the V bit was set in the
stream's most recent start of a keyframe (i.e. the SS field was stream's most recent start of a keyframe (i.e., the SS field was
present) and the F bit is set to 0 (i.e. non-flexible scalability present) and the F bit is set to 0 (i.e., non-flexible scalability
mode is in use), then this bit MUST be set on every packet. mode is in use), then this bit MUST be set on every packet.
P: Inter-picture predicted frame. When set to zero, the frame does P: Inter-picture predicted frame. When set to 0, the frame does not
not utilize inter-picture prediction. In this case, up-switching utilize inter-picture prediction. In this case, up-switching to a
to a current spatial layer's frame is possible from directly lower current spatial layer's frame is possible from a directly lower
spatial layer frame. P SHOULD also be set to zero when encoding a spatial-layer frame. P SHOULD also be set to 0 when encoding a
layer synchronization frame in response to an LRR layer synchronization frame in response to a Layer Refresh Request
[I-D.ietf-avtext-lrr] message (see Section 5.3). When P is set to (LRR) [RFC9627] message (see Section 5.3). When P is set to 0,
zero, the TID field (described below) MUST also be set to 0 (if the TID field (described below) MUST also be set to 0 (if
present). Note that the P bit does not forbid intra-picture, present). Note that the P bit does not forbid intra-picture,
inter-layer prediction from earlier frames of the same picture, if inter-layer prediction from earlier frames of the same picture, if
any. any.
L: Layer indices present. When set to one, the one or two octets L: Layer indices present. When set to 1, the one or two octets
following the mandatory first octet and the PID (if present) is as following the mandatory first octet and the PID (if present) is as
described by "Layer indices" below. If the F bit (described described by "Layer indices" below. If the F bit (described
below) is set to 1 (indicating flexible mode), then only one octet below) is set to 1 (indicating flexible mode), then only one octet
is present for the layer indices. Otherwise if the F bit is set is present for the layer indices. Otherwise, if the F bit is set
to 0 (indicating non-flexible mode), then two octets are present to 0 (indicating non-flexible mode), then two octets are present
for the layer indices. for the layer indices.
F: Flexible mode. F set to one indicates flexible mode and if the P F: Flexible mode. When set to 1, this indicates flexible mode; if
bit is also set to one, then the octets following the mandatory the P bit is also set to 1, then the octets following the
first octet, the PID, and layer indices (if present) are as mandatory first octet, the PID, and layer indices (if present) are
described by "Reference indices" below. This MUST only be set to as described by "reference indices" below. This bit MUST only be
1 if the I bit is also set to one; if the I bit is set to zero, set to 1 if the I bit is also set to 1; if the I bit is set to 0,
then this MUST also be set to zero and ignored by receivers. then this bit MUST also be set to 0 and ignored by receivers.
(Flexible mode's Reference indices are defined as offsets from the (Flexible mode's reference indices are defined as offsets from the
Picture ID field, so they would have no meaning if I were not Picture ID field, so they would have no meaning if I were not
set.) The value of this F bit MUST only change on the first set.) The value of the F bit MUST only change on the first packet
packet of a key picture. A key picture is a picture whose base of a key picture. A "key picture" is a picture whose base
spatial layer frame is a key frame, and which thus completely spatial-layer frame is a keyframe, and thus one which completely
resets the encoder state. This packet will have its P bit equal resets the encoder state. This packet will have its P bit equal
to zero, SID or L bit (described below) equal to zero, and B bit to 0, SID or L bit (described below) equal to 0, and B bit
(described below) equal to 1. (described below) equal to 1.
B: Start of a frame. MUST be set to 1 if the first payload octet of B: Start of a frame. This bit MUST be set to 1 if the first payload
the RTP packet is the beginning of a new VP9 frame, and MUST NOT octet of the RTP packet is the beginning of a new VP9 frame;
be 1 otherwise. Note that this frame might not be the first frame otherwise, it MUST NOT be 1. Note that this frame might not be
of a picture. the first frame of a picture.
E: End of a frame. MUST be set to 1 for the final RTP packet of a E: End of a frame. This bit MUST be set to 1 for the final RTP
VP9 frame, and 0 otherwise. This enables a decoder to finish packet of a VP9 frame; otherwise, it MUST be 0. This enables a
decoding the frame, where it otherwise may need to wait for the decoder to finish decoding the frame, where it otherwise may need
next packet to explicitly know that the frame is complete. Note to wait for the next packet to explicitly know that the frame is
that, if spatial scalability is in use, more frames from the same complete. Note that, if spatial scalability is in use, more
picture may follow; see the description of the B bit above. frames from the same picture may follow; see the description of
the B bit above.
V: Scalability structure (SS) data present. When set to one, the V: Scalability Structure (SS) data present. When set to 1, the
OPTIONAL SS data MUST be present in the payload descriptor. OPTIONAL SS data MUST be present in the payload descriptor.
Otherwise, the SS data MUST NOT be present. Otherwise, the SS data MUST NOT be present.
Z: Not a reference frame for upper spatial layers. If set to 1, Z: Not a reference frame for upper spatial layers. If set to 1,
indicates that frames with higher spatial layers SID+1 and greater indicates that frames with higher spatial layers SID+1 and greater
of the current and following pictures do not depend on the current of the current and following pictures do not depend on the current
spatial layer SID frame. This enables a decoder which is spatial-layer SID frame. This enables a decoder that is targeting
targeting a higher spatial layer to know that it can safely a higher spatial layer to know that it can safely discard this
discard this packet's frame without processing it, without having packet's frame without processing it, without having to wait for
to wait for the "D" bit in the higher-layer frame (see below). the D bit in the higher-layer frame (see below).
The mandatory first octet is followed by the extension data fields The mandatory first octet is followed by the extension data fields
that are enabled: that are enabled:
M: The most significant bit of the first octet is an extension flag. M: The most significant bit of the first octet is an extension flag.
The field MUST be present if the I bit is equal to one. If M is The field MUST be present if the I bit is equal to one. If M is
set, the PID field MUST contain 15 bits; otherwise, it MUST set, the PID field MUST contain 15 bits; otherwise, it MUST
contain 7 bits. See PID below. contain 7 bits. See PID below.
Picture ID (PID): Picture ID represented in 7 or 15 bits, depending Picture ID (PID): Picture ID represented in 7 or 15 bits, depending
on the M bit. This is a running index of the pictures, where the on the M bit. This is a running index of the pictures, where the
sender increments the value by 1 for each picture it sends. (Note sender increments the value by 1 for each picture it sends.
however that because a middlebox can discard pictures where (Note, however, that because a middlebox can discard pictures
permitted by the scalability structure, Picture IDs as received by where permitted by the SS, Picture IDs as received by a receiver
a receiver might not be contiguous.) This field MUST be present might not be contiguous.) This field MUST be present if the I bit
if the I bit is equal to one. If M is set to zero, 7 bits carry is equal to one. If M is set to 0, 7 bits carry the PID; else, if
the PID; else if M is set to one, 15 bits carry the PID in network M is set to 1, 15 bits carry the PID in network byte order. The
byte order. The sender may choose between a 7- or 15-bit index. sender may choose between a 7- or 15-bit index. The PID SHOULD
The PID SHOULD start on a random number, and MUST wrap after start on a random number and MUST wrap after reaching the maximum
reaching the maximum ID (0x7f or 0x7fff depending on the index ID (0x7f or 0x7fff depending on the index size chosen). The
size chosen). The receiver MUST NOT assume that the number of receiver MUST NOT assume that the number of bits in the PID stays
bits in PID stay the same through the session. If this field the same through the session. If this field transitions from 7
transitions from 7-bits to 15-bits, the value is zero-extended bits to 15 bits, the value is zero-extended (i.e., the value after
(i.e. the value after 0x6e is 0x006f); if the field transitions 0x6e is 0x006f); if the field transitions from 15 bits to 7 bits,
from 15 bits to 7 bits, it is truncated (i.e. the value after it is truncated (i.e., the value after 0x1bbe is 0xbf).
0x1bbe is 0xbf).
In the non-flexible mode (when the F bit is set to 0), this PID is In the non-flexible mode (when the F bit is set to 0), this PID is
used as an index to the picture group (PG) specified in the SS used as an index to the PG specified in the SS data below. In
data below. In this mode, the PID of the key frame corresponds to this mode, the PID of the keyframe corresponds to the first
the first specified frame in the PG. Then subsequent PIDs are specified frame in the PG. Then subsequent PIDs are mapped to
mapped to subsequently specified frames in the PG (modulo N_G, subsequently specified frames in the PG (modulo N_G, specified in
specified in the SS data below), respectively. the SS data below), respectively.
All frames of the same picture MUST have the same PID value. All frames of the same picture MUST have the same PID value.
Frames (and their corresponding pictures) with the VP9 show_frame Frames (and their corresponding pictures) with the VP9 show_frame
field equal to 0 MUST have distinct PID values from subsequent field equal to 0 MUST have distinct PID values from subsequent
pictures with show_frame equal to 1. Thus, a Picture as defined pictures with show_frame equal to 1. Thus, a picture (as defined
in this specification is different than a VP9 Superframe. in this specification) is different than a VP9 superframe.
All frames of the same picture MUST have the same value for All frames of the same picture MUST have the same value for
show_frame. show_frame.
Layer indices: This information is optional but RECOMMENDED whenever Layer indices: This field is optional but RECOMMENDED whenever
encoding with layers. For both flexible and non-flexible modes, encoding with layers. For both flexible and non-flexible modes,
one octet is used to specify a layer frame's temporal layer ID one octet is used to specify a layer frame's temporal-layer ID
(TID) and spatial layer ID (SID) as shown both in Figure 2 and (TID) and spatial-layer ID (SID) as shown both in Figure 2 and
Figure 3. Additionally, a bit (U) is used to indicate that the Figure 3. Additionally, a bit (U) is used to indicate that the
current frame is a "switching up point" frame. Another bit (D) is current frame is a "switching up point" frame. Another bit (D) is
used to indicate whether inter-layer prediction is used for the used to indicate whether inter-layer prediction is used for the
current frame. current frame.
In the non-flexible mode (when the F bit is set to 0), another In the non-flexible mode (when the F bit is set to 0), another
octet is used to represent temporal layer 0 index (TL0PICIDX), as octet is used to represent Temporal Layer 0 Picture Index (8 bits)
depicted in Figure 3. The TL0PICIDX is present so that all (TL0PICIDX), as depicted in Figure 3. The TL0PICIDX is present so
minimally required frames - the base temporal layer frames - can that all minimally required frames (the base temporal-layer
be tracked. frames) can be tracked.
The TID and SID fields indicate the temporal and spatial layers The TID and SID fields indicate the temporal and spatial layers
and can help middleboxes and endpoints quickly identify which and can help middleboxes and endpoints quickly identify which
layer a packet belongs to. layer a packet belongs to.
TID: The temporal layer ID of current frame. In the case of non- TID: The temporal-layer ID of the current frame. In the case of
flexible mode, if PID is mapped to a picture in a specified PG, non-flexible mode, if a PID is mapped to a picture in a
then the value of TID MUST match the corresponding TID value of specified PG, then the value of the TID MUST match the
the mapped picture in the PG. corresponding TID value of the mapped picture in the PG.
U: Switching up point. If this bit is set to 1 for the current U: Switching up point. If this bit is set to 1 for the current
picture with temporal layer ID equal to TID, then "switch up" picture with a temporal-layer ID equal to value T, then
to a higher frame rate is possible as subsequent higher "switching up" to a higher frame rate is possible as subsequent
temporal layer pictures will not depend on any picture before higher temporal-layer pictures will not depend on any picture
the current picture (in coding order) with temporal layer ID before the current picture (in coding order) with a temporal-
greater than TID. layer ID value greater than T.
SID: The spatial layer ID of current frame. Note that frames SID: The spatial-layer ID of the current frame. Note that frames
with spatial layer SID > 0 may be dependent on decoded spatial with spatial-layer SID > 0 may be dependent on decoded spatial-
layer SID-1 frame within the same picture. Different frames of layer SID-1 frame within the same picture. Different frames of
the same picture MUST have distinct spatial layer IDs, and the same picture MUST have distinct spatial-layer IDs, and
frames' spatial layers MUST appear in increasing order within frames' spatial layers MUST appear in increasing order within
the frame. the frame.
D: Inter-layer dependency used. MUST be set to one if and only D: Inter-layer dependency is used. D MUST be set to 1 if and
if the current spatial layer SID frame depends on spatial layer only if the current spatial-layer SID frame depends on spatial-
SID-1 frame of the same picture, otherwise MUST be set to zero. layer SID-1 frame of the same picture; otherwise, it MUST be
For the base layer frame (with SID equal to 0), this D bit MUST set to 0. For the base-layer frame (with SID equal to 0), the
be set to zero. D bit MUST be set to 0.
TL0PICIDX: 8 bits temporal layer zero index. TL0PICIDX is only TL0PICIDX: Temporal Layer 0 Picture Index (8 bits). TL0PICIDX is
present in the non-flexible mode (F = 0). This is a running only present in the non-flexible mode (F = 0). This is a
index for the temporal base layer pictures, i.e., the pictures running index for the temporal base-layer pictures, i.e., the
with TID set to 0. If TID is larger than 0, TL0PICIDX pictures with a TID set to 0. If the TID is larger than 0,
indicates which temporal base layer picture the current picture TL0PICIDX indicates which temporal base-layer picture the
depends on. TL0PICIDX MUST be incremented by 1 when TID is current picture depends on. TL0PICIDX MUST be incremented by 1
equal to 0. The index SHOULD start on a random number, and when the TID is equal to 0. The index SHOULD start on a random
MUST restart at 0 after reaching the maximum number 255. number and MUST restart at 0 after reaching the maximum number
255.
Reference indices: When P and F are both set to one, indicating a Reference indices: When P and F are both set to 1, indicating a non-
non-key frame in flexible mode, then at least one reference index keyframe in flexible mode, then at least one reference index MUST
MUST be specified as below. Additional reference indices (total be specified as below. Additional reference indices (a total of
of up to 3 reference indices are allowed) may be specified using up to three reference indices are allowed) may be specified using
the N bit below. When either P or F is set to zero, then no the N bit below. When either P or F is set to 0, then no
reference index is specified. reference index is specified.
P_DIFF: The reference index (in 7 bits) specified as the relative P_DIFF: The reference index (in 7 bits) specified as the relative
PID from the current picture. For example, when P_DIFF=3 on a PID from the current picture. For example, when P_DIFF=3 on a
packet containing the picture with PID 112 means that the packet containing the picture with PID 112 means that the
picture refers back to the picture with PID 109. This picture refers back to the picture with PID 109. This
calculation is done modulo the size of the PID field, i.e., calculation is done modulo the size of the PID field, i.e.,
either 7 or 15 bits. A P_DIFF value of 0 is invalid. either 7 or 15 bits. A P_DIFF value of 0 is invalid.
N: 1 if there is additional P_DIFF following the current P_DIFF. N: 1 if there is additional P_DIFF following the current P_DIFF.
4.2.1. Scalability Structure (SS): 4.2.1. Scalability Structure (SS)
The scalability structure (SS) data describes the resolution of each The SS data describes the resolution of each frame within a picture
frame within a picture as well as the inter-picture dependencies for as well as the inter-picture dependencies for a PG. If the VP9
a picture group (PG). If the VP9 payload descriptor's "V" bit is payload descriptor's V bit is set, the SS data is present in the
set, the SS data is present in the position indicated in Figure 2 and position indicated in Figures 2 and 3.
Figure 3.
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
V: | N_S |Y|G|-|-|-| V: | N_S |Y|G|-|-|-|
+-+-+-+-+-+-+-+-+ -\ +-+-+-+-+-+-+-+-+ -\
Y: | WIDTH | (OPTIONAL) . Y: | WIDTH | (OPTIONAL) .
+ + . + + .
| | (OPTIONAL) . | | (OPTIONAL) .
+-+-+-+-+-+-+-+-+ . - N_S + 1 times +-+-+-+-+-+-+-+-+ . - N_S + 1 times
| HEIGHT | (OPTIONAL) . | HEIGHT | (OPTIONAL) .
+ + . + + .
| | (OPTIONAL) . | | (OPTIONAL) .
+-+-+-+-+-+-+-+-+ -/ +-+-+-+-+-+-+-+-+ -/
G: | N_G | (OPTIONAL) G: | N_G | (OPTIONAL)
+-+-+-+-+-+-+-+-+ -\ +-+-+-+-+-+-+-+-+ -\
N_G: | TID |U| R |-|-| (OPTIONAL) . N_G: | TID |U| R |-|-| (OPTIONAL) .
+-+-+-+-+-+-+-+-+ -\ . - N_G times +-+-+-+-+-+-+-+-+ -\ . - N_G times
| P_DIFF | (OPTIONAL) . - R times . | P_DIFF | (OPTIONAL) . - R times .
+-+-+-+-+-+-+-+-+ -/ -/ +-+-+-+-+-+-+-+-+ -/ -/
Figure 4 Figure 4: VP9 Scalability Structure
N_S: N_S + 1 indicates the number of spatial layers present in the N_S: Number of Spatial Layers Minus 1. N_S + 1 indicates the number
VP9 stream. of spatial layers present in the VP9 stream.
Y: Each spatial layer's frame resolution present. When set to one, Y: Each spatial layer's frame resolution is present. When set to 1,
the OPTIONAL WIDTH (2 octets) and HEIGHT (2 octets) MUST be the OPTIONAL WIDTH (2 octets) and HEIGHT (2 octets) MUST be
present for each layer frame. Otherwise, the resolution MUST NOT present for each layer frame. Otherwise, the resolution MUST NOT
be present. be present.
G: PG description present flag. G: The PG description present flag.
-: Bit reserved for future use. MUST be set to zero and MUST be -: A bit reserved for future use. It MUST be set to 0 and MUST be
ignored by the receiver. ignored by the receiver.
N_G: N_G indicates the number of pictures in a Picture Group (PG). N_G: N_G indicates the number of pictures in a PG. If N_G is
If N_G is greater than 0, then the SS data allows the inter- greater than 0, then the SS data allows the inter-picture
picture dependency structure of the VP9 stream to be pre-declared, dependency structure of the VP9 stream to be pre-declared, rather
rather than indicating it on the fly with every packet. If N_G is than indicating it on the fly with every packet. If N_G is
greater than 0, then for N_G pictures in the PG, each picture's greater than 0, then for N_G pictures in the PG, each picture's
temporal layer ID (TID), switch up point (U), and the Reference temporal-layer ID (TID), switch up point (U), and reference
indices (P_DIFFs) are specified. indices (P_DIFFs) are specified.
The first picture specified in the PG MUST have TID set to 0. The first picture specified in the PG MUST have a TID set to 0.
G set to 0 or N_G set to 0 indicates that either there is only one G set to 0 or N_G set to 0 indicates that either there is only one
temporal layer (for non-flexible mode) or no fixed inter-picture temporal layer (for non-flexible mode) or no fixed inter-picture
dependency information is present (for flexible mode) going dependency information is present (for flexible mode) going
forward in the bitstream. forward in the bitstream.
Note that for a given picture, all frames follow the same inter- Note that for a given picture, all frames follow the same inter-
picture dependency structure. However, the frame rate of each picture dependency structure. However, the frame rate of each
spatial layer can be different from each other and this can be spatial layer can be different from each other; this can be
described with the use of the D bit described above. The described with the use of the D bit described above. The
specified dependency structure in the SS data MUST be for the specified dependency structure in the SS data MUST be for the
highest frame rate layer. highest frame rate layer.
In a scalable stream sent with a fixed pattern, the SS data SHOULD be In a scalable stream sent with a fixed pattern, the SS data SHOULD be
included in the first packet of every key frame. This is a packet included in the first packet of every key frame. This is a packet
with P bit equal to zero, SID or L bit equal to zero, and B bit equal with the P bit equal to 0, SID or L bit equal to 0, and B bit equal
to 1. The SS data MUST only be changed on the picture that to 1. The SS data MUST only be changed on the picture that
corresponds to the first picture specified in the previous SS data's corresponds to the first picture specified in the previous SS data's
PG (if the previous SS data's N_G was greater than 0). PG (if the previous SS data's N_G was greater than 0).
4.3. Frame Fragmentation 4.3. Frame Fragmentation
VP9 frames are fragmented into packets, in RTP sequence number order, VP9 frames are fragmented into packets in RTP sequence number order:
beginning with a packet with the B bit set, and ending with a packet beginning with a packet with the B bit set and ending with a packet
with the E bit set. There is no mechanism for finer-grained access with the E bit set. There is no mechanism for finer-grained access
to parts of a VP9 frame. to parts of a VP9 frame.
4.4. Scalable encoding considerations 4.4. Scalable Encoding Considerations
In addition to the use of reference frames, VP9 has several In addition to the use of reference frames, VP9 has several
additional forms of inter-frame dependencies, largely involving additional forms of inter-frame dependencies, largely involving
probability tables for the entropy and tree encoders. In VP9 syntax, probability tables for the entropy and tree encoders. In VP9 syntax,
the syntax element "error_resilient_mode" resets this additional the syntax element "error_resilient_mode" resets this additional
inter-frame data, allowing a frame's syntax to be decoded inter-frame data, allowing a frame's syntax to be decoded
independently. independently.
Due to the requirements of scalable streams, a VP9 encoder producing Due to the requirements of scalable streams, a VP9 encoder producing
a scalable stream needs to ensure that a frame does not depend on a a scalable stream needs to ensure that a frame does not depend on a
previous frame (of the same or a previous picture) that can previous frame (of the same or a previous picture) that can
legitimately be removed from the stream. Thus, a frame that follows legitimately be removed from the stream. Thus, a frame that follows
a frame that might be removed (in full decode order) MUST be encoded a frame that might be removed (in full decode order) MUST be encoded
with "error_resilient_mode" set to true. with "error_resilient_mode" set to true.
For spatially-scalable streams, this means that For spatially scalable streams, this means that
"error_resilient_mode" needs to be turned on for the base spatial "error_resilient_mode" needs to be turned on for the base spatial
layer; it can however be turned off for higher spatial layers, layer; however, it can be turned off for higher spatial layers,
assuming they are sent with inter-layer dependency (i.e. with the "D" assuming they are sent with inter-layer dependency (i.e., with the D
bit set). For streams that are only temporally-scalable without bit set). For streams that are only temporally scalable without
spatial scalability, "error_resilient_mode" can additionally be spatial scalability, "error_resilient_mode" can additionally be
turned off for any picture that immediately follows a temporal layer turned off for any picture that immediately follows a temporal-layer
0 frame. 0 frame.
4.5. Examples of VP9 RTP Stream 4.5. Examples of VP9 RTP Stream
4.5.1. Reference picture use for scalable structure
4.5.1. Reference Picture Use for Scalable Structure
As discussed in Section 3, the VP9 codec can maintain up to eight As discussed in Section 3, the VP9 codec can maintain up to eight
reference frames, of which up to three can be referenced or updated reference frames, of which up to three can be referenced or updated
by any new frame. This section illustrates one way that a scalable by any new frame. This section illustrates one way that a scalable
structure (with three spatial layers and three temporal layers) can structure (with three spatial layers and three temporal layers) can
be constructed using these reference frames. be constructed using these reference frames.
+==========+=========+============+=========+ +==========+=========+============+=========+
| Temporal | Spatial | References | Updates | | Temporal | Spatial | References | Updates |
+==========+=========+============+=========+ +==========+=========+============+=========+
skipping to change at page 14, line 40 skipping to change at line 635
+----------+---------+------------+---------+ +----------+---------+------------+---------+
| 1 | 2 | 2,4 | 5 | | 1 | 2 | 2,4 | 5 |
+----------+---------+------------+---------+ +----------+---------+------------+---------+
| 2 | 0 | 3 | 6 | | 2 | 0 | 3 | 6 |
+----------+---------+------------+---------+ +----------+---------+------------+---------+
| 2 | 1 | 4,6 | 7 | | 2 | 1 | 4,6 | 7 |
+----------+---------+------------+---------+ +----------+---------+------------+---------+
| 2 | 2 | 5,7 | - | | 2 | 2 | 5,7 | - |
+----------+---------+------------+---------+ +----------+---------+------------+---------+
Table 1: Example scalability structure Table 1: Example Scalability Structure
This structure is constructed such that the "U" bit can always be This structure is constructed such that the U bit can always be set.
set.
5. Feedback Messages and Header Extensions 5. Feedback Messages and Header Extensions
5.1. Reference Picture Selection Indication (RPSI) 5.1. Reference Picture Selection Indication (RPSI)
The reference picture selection index is a payload-specific feedback The RPSI is a payload-specific feedback message defined within the
message defined within the RTCP-based feedback format. The RPSI RTCP-based feedback format. The RPSI message is generated by a
message is generated by a receiver and can be used in two ways. receiver and can be used in two ways: either it can signal a
Either it can signal a preferred reference picture when a loss has preferred reference picture when a loss has been detected by the
been detected by the decoder -- preferably then a reference that the decoder (preferably a reference that the decoder knows is perfect) or
decoder knows is perfect -- or, it can be used as positive feedback it can be used as positive feedback information to acknowledge
information to acknowledge correct decoding of certain reference correct decoding of certain reference pictures. The positive
pictures. The positive feedback method is useful for VP9 used for feedback method is useful for VP9 used for point-to-point (unicast)
point to point (unicast) communication. The use of RPSI for VP9 is communication. The use of RPSI for VP9 is preferably combined with a
preferably combined with a special update pattern of the codec's two special update pattern of the codec's two special reference frames --
special reference frames -- the golden frame and the altref frame -- the golden frame and the altref frame -- in which they are updated in
in which they are updated in an alternating leapfrog fashion. When a an alternating leapfrog fashion. When a receiver has received and
receiver has received and correctly decoded a golden or altref frame, correctly decoded a golden or altref frame, and that frame had a
and that frame had a Picture ID in the payload descriptor, the Picture ID in the payload descriptor, the receiver can acknowledge
receiver can acknowledge this simply by sending an RPSI message back this simply by sending an RPSI message back to the sender. The
to the sender. The message body (i.e., the "native RPSI bit string" message body (i.e., the "native RPSI bit string" in [RFC4585]) is
in [RFC4585]) is simply the (7 or 15 bit) Picture ID of the received simply the (7- or 15-bit) Picture ID of the received frame.
frame.
Note: because all frames of the same picture must have the same | Note: because all frames of the same picture must have the same
inter-picture reference structure, there is no need for a message to | inter-picture reference structure, there is no need for a
specify which frame is being selected. | message to specify which frame is being selected.
5.2. Full Intra Request (FIR) 5.2. Full Intra Request (FIR)
The Full Intra Request (FIR) [RFC5104] RTCP feedback message allows a The Full Intra Request (FIR) [RFC5104] RTCP feedback message allows a
receiver to request a full state refresh of an encoded stream. receiver to request a full state refresh of an encoded stream.
Upon receipt of an FIR request, a VP9 sender MUST send a picture with Upon receipt of a FIR request, a VP9 sender MUST send a picture with
a keyframe for its spatial layer 0 layer frame, and then send frames a keyframe for its spatial-layer 0 layer frame and then send frames
without inter-picture prediction (P=0) for any higher layer frames. without inter-picture prediction (P=0) for any higher-layer frames.
5.3. Layer Refresh Request (LRR) 5.3. Layer Refresh Request (LRR)
The Layer Refresh Request (LRR) [I-D.ietf-avtext-lrr] allows a The Layer Refresh Request (LRR) [RFC9627] allows a receiver to
receiver to request a single layer of a spatially or temporally request a single layer of a spatially or temporally encoded stream to
encoded stream to be refreshed, without necessarily affecting the be refreshed without necessarily affecting the stream's other layers.
stream's other layers.
+---------------+---------------+ +---------------+---------------+
|0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|
+---------------+---------+-----+ +---------------+---------+-----+
| RES | TID | RES | SID | | RES | TID | RES | SID |
+---------------+---------+-----+ +---------------+---------+-----+
Figure 5 Figure 5: LRR Index Format
Figure 5 shows the format of LRR's layer index fields for VP9 Figure 5 shows the format of an LRR's layer index fields for VP9
streams. The two "RES" fields MUST be set to 0 on transmission and streams. The two "RES" fields MUST be set to 0 on transmission and
ingnored on reception. See Section 4.2 for details on the TID and ignored on reception. See Section 4.2 for details on the TID and SID
SID fields. fields.
Identification of a layer refresh frame can be derived from the Identification of a layer refresh frame can be derived from the
reference IDs of each frame by backtracking the dependency chain reference IDs of each frame by backtracking the dependency chain
until reaching a point where only decodable frames are being until reaching a point where only decodable frames are being
referenced. Therefore it's recommended for both the flexible and the referenced. Therefore, it's recommended for both the flexible and
non-flexible mode that, when switching up points are being encoded in the non-flexible mode that, when switching up points are being
response to a LRR, those packets should contain layer indices and the encoded in response to an LRR, those packets contain layer indices
reference field(s) so that the decoder or a selective forwarding and the reference field or fields so that the decoder or selective
middleboxes [RFC7667] can make this derivation. forwarding middleboxes [RFC7667] can make this derivation.
Example: Example:
LRR {1,0}, {2,1} is sent by an MCU when it is currently relaying LRR {1,0}, {2,1} is sent by a Multipoint Control Unit (MCU) when it
{1,0} to a receiver and which wants to upgrade to {2,1}. In response is currently relaying {1,0} to a receiver that wants to upgrade to
the encoder should encode the next frames in layers {1,1} and {2,1} {2,1}. In response, the encoder should encode the next frames in
by only referring to frames in {1,0}, or {0,0}. layers {1,1} and {2,1} by only referring to frames in {1,0} or {0,0}.
In the non-flexible mode, periodic upgrade frames can be defined by In the non-flexible mode, periodic upgrade frames can be defined by
the layer structure of the SS, thus periodic upgrade frames can be the layer structure of the SS; thus, periodic upgrade frames can be
automatically identified by the picture ID. automatically identified by the Picture ID.
6. Payload Format Parameters 6. Payload Format Parameters
This payload format has three optional parameters, "max-fr", "max- This payload format has three optional parameters: max-fr, max-fs,
fs", and "profile-id". and profile-id.
The max-fr and max-fs parameters are used to signal the capabilities The max-fr and max-fs parameters are used to signal the capabilities
of a receiver implementation. If the implementation is willing to of a receiver implementation. If the implementation is willing to
receive media, both parameters MUST be provided. These parameters receive media, both parameters MUST be provided. These parameters
MUST NOT be used for any other purpose. A media sender SHOULD NOT MUST NOT be used for any other purpose. A media sender SHOULD NOT
send media with a frame rate or frame size exceeding the max-fr and send media with a frame rate or frame size exceeding the max-fr and
max-fs values signaled. (There may be scenarios, such as pre-encoded max-fs values signaled. (There may be scenarios, such as pre-encoded
media or selective forwarding middleboxes [RFC7667], where a media media or selective forwarding middleboxes [RFC7667], where a media
sender does not have media available that fits within a receivers sender does not have media available that fits within a receiver's
max-fs and max-fr value; in such scenarios, a sender MAY exceed the max-fs and max-fr values; in such scenarios, a sender MAY exceed the
signaled values.) signaled values.)
max-fr: The value of max-fr is an integer indicating the maximum max-fr: The value of max-fr is an integer indicating the maximum
frame rate in units of frames per second that the decoder is frame rate in units of frames per second that the decoder is
capable of decoding. capable of decoding.
max-fs: The value of max-fs is an integer indicating the maximum max-fs: The value of max-fs is an integer indicating the maximum
frame size in units of macroblocks that the decoder is capable of frame size in units of macroblocks that the decoder is capable of
decoding. decoding.
The decoder is capable of decoding this frame size as long as the The decoder is capable of decoding this frame size as long as the
width and height of the frame in macroblocks are less than width and height of the frame in macroblocks are each less than
int(sqrt(max-fs * 8)) - for instance, a max-fs of 1200 (capable of int(sqrt(max-fs * 8)); for instance, a max-fs of 1200 (capable of
supporting 640x480 resolution) will support widths and heights up supporting 640x480 resolution) will support widths and heights up
to 1552 pixels (97 macroblocks). to 1552 pixels (97 macroblocks).
profile-id: The value of profile-id is an integer indicating the profile-id: The value of profile-id is an integer indicating the
default coding profile, the subset of coding tools that may have default coding profile (the subset of coding tools that may have
been used to generate the stream or that the receiver supports). been used to generate the stream or that the receiver supports).
Table 2 lists all of the profiles defined in section 7.2 of Table 2 lists all of the profiles defined in Section 7.2 of
[VP9-BITSTREAM] and the corresponding integer values to be used. [VP9-BITSTREAM] and the corresponding integer values to be used.
If no profile-id is present, Profile 0 MUST be inferred. (The If no profile-id is present, Profile 0 MUST be inferred. (The
profile-id parameter was added relatively late in the development profile-id parameter was added relatively late in the development
of this specification, so some existing implementations may not of this specification, so some existing implementations may not
send it.) send it.)
Informative note: See Table 3 for capabilities of coding profiles Informative note: See Table 3 for capabilities of coding profiles
defined in section 7.2 of [VP9-BITSTREAM]. defined in Section 7.2 of [VP9-BITSTREAM].
A receiver MUST ignore any parameter unspecified in this A receiver MUST ignore any parameter unspecified in this
specification. specification.
+=========+============+ +=========+============+
| Profile | profile-id | | Profile | profile-id |
+=========+============+ +=========+============+
| 0 | 0 | | 0 | 0 |
+---------+------------+ +---------+------------+
| 1 | 1 | | 1 | 1 |
+---------+------------+ +---------+------------+
| 2 | 2 | | 2 | 2 |
+---------+------------+ +---------+------------+
| 3 | 3 | | 3 | 3 |
+---------+------------+ +---------+------------+
Table 2: Table of Table 2:
profile-id integer Correspondence between
values representing profile-id to VP9
the VP9 profile Profile Integer
corresponding to the
set of coding tools
supported.
+=========+===========+=================+==========================+ +=========+===========+=================+==========================+
| Profile | Bit Depth | SRGB Colorspace | Chroma Subsampling | | Profile | Bit Depth | SRGB Colorspace | Chroma Subsampling |
+=========+===========+=================+==========================+ +=========+===========+=================+==========================+
| 0 | 8 | No | YUV 4:2:0 | | 0 | 8 | No | YUV 4:2:0 |
+---------+-----------+-----------------+--------------------------+ +---------+-----------+-----------------+--------------------------+
| 1 | 8 | Yes | YUV 4:2:2,4:4:0 or 4:4:4 | | 1 | 8 | Yes | YUV 4:2:2,4:4:0 or 4:4:4 |
+---------+-----------+-----------------+--------------------------+ +---------+-----------+-----------------+--------------------------+
| 2 | 10 or 12 | No | YUV 4:2:0 | | 2 | 10 or 12 | No | YUV 4:2:0 |
+---------+-----------+-----------------+--------------------------+ +---------+-----------+-----------------+--------------------------+
| 3 | 10 or 12 | Yes | YUV 4:2:2,4:4:0 or 4:4:4 | | 3 | 10 or 12 | Yes | YUV 4:2:2,4:4:0 or 4:4:4 |
+---------+-----------+-----------------+--------------------------+ +---------+-----------+-----------------+--------------------------+
Table 3: Table of profile capabilities. Table 3: Profile Capabilities
| Note: SRGB (often sRGB) = Standard Red-Green-Blue
6.1. SDP Parameters 6.1. SDP Parameters
6.1.1. Mapping of Media Subtype Parameters to SDP 6.1.1. Mapping of Media Subtype Parameters to SDP
The media type video/VP9 string is mapped to fields in the Session The media type video/vp9 string is mapped to fields in the Session
Description Protocol (SDP) [RFC8866] as follows: Description Protocol (SDP) [RFC8866] as follows:
* The media name in the "m=" line of SDP MUST be video. * The media name in the "m=" line of SDP MUST be video.
* The encoding name in the "a=rtpmap" line of SDP MUST be VP9 (the * The encoding name in the "a=rtpmap" line of SDP MUST be VP9 (the
media subtype). media subtype).
* The clock rate in the "a=rtpmap" line MUST be 90000. * The clock rate in the "a=rtpmap" line MUST be 90000.
* The parameters "max-fr" and "max-fs" MUST be included in the * The parameters max-fr and max-fs MUST be included in the "a=fmtp"
"a=fmtp" line of SDP if the receiver wishes to declare its line of SDP if the receiver wishes to declare its receiver
receiver capabilities. These parameters are expressed as a media capabilities. These parameters are expressed as a media subtype
subtype string, in the form of a semicolon separated list of string in the form of a semicolon-separated list of
parameter=value pairs. parameter=value pairs.
* The OPTIONAL parameter profile-id, when present, SHOULD be * The OPTIONAL parameter profile-id, when present, SHOULD be
included in the "a=fmtp" line of SDP. This parameter is expressed included in the "a=fmtp" line of SDP. This parameter is expressed
as a media subtype string, in the form of a parameter=value pair. as a media subtype string in the form of a parameter=value pair.
When the parameter is not present, a value of 0 MUST be inferred When the parameter is not present, a value of 0 MUST be inferred
for profile-id. for profile-id.
6.1.1.1. Example 6.1.1.1. Example
An example of media representation in SDP is as follows: An example of media representation in SDP is as follows:
m=video 49170 RTP/AVPF 98 m=video 49170 RTP/AVPF 98
a=rtpmap:98 VP9/90000 a=rtpmap:98 VP9/90000
a=fmtp:98 max-fr=30;max-fs=3600;profile-id=0 a=fmtp:98 max-fr=30;max-fs=3600;profile-id=0
skipping to change at page 19, line 20 skipping to change at line 842
* The parameter identifying a media format configuration for VP9 is * The parameter identifying a media format configuration for VP9 is
profile-id. This media format configuration parameter MUST be profile-id. This media format configuration parameter MUST be
used symmetrically; that is, the answerer MUST either maintain used symmetrically; that is, the answerer MUST either maintain
this configuration parameter or remove the media format (payload this configuration parameter or remove the media format (payload
type) completely if it is not supported. type) completely if it is not supported.
* The max-fr and max-fs parameters are used declaratively to * The max-fr and max-fs parameters are used declaratively to
describe receiver capabilities, even in the Offer/Answer model. describe receiver capabilities, even in the Offer/Answer model.
The values in an answer are used to describe the answerer's The values in an answer are used to describe the answerer's
capabilities, and thus their values are set independently of the capabilities; thus, their values are set independently of the
values in the offer. values in the offer.
* To simplify the handling and matching of these configurations, the * To simplify the handling and matching of these configurations, the
same RTP payload type number used in the offer SHOULD also be used same RTP payload type number used in the offer SHOULD also be used
in the answer and in a subsequent offer, as specified in in the answer and in a subsequent offer, as specified in
[RFC3264]. An answer or subsequent offer MUST NOT contain the [RFC3264]. An answer or subsequent offer MUST NOT contain the
payload type number used in the offer unless the profile-id value payload type number used in the offer unless the profile-id value
is exactly the same as in the original offer. However, max-fr and is exactly the same as in the original offer. However, max-fr and
max-fs parameters MAY be changed in subsequent offers and answers, max-fs parameters MAY be changed in subsequent offers and answers,
with the same payload type number, if an endpoint wishes to change with the same payload type number, if an endpoint wishes to change
its declared receiver capabilities. its declared receiver capabilities.
7. Media Type Definition 7. Media Type Definition
This registration is done using the template defined in [RFC6838] and This registration uses the template defined in [RFC6838] and
following [RFC4855]. following [RFC4855].
Type name: Type name: video
video
Subtype name:
VP9
Required parameters:
N/A.
Optional parameters: Subtype name: VP9
There are three optional parameters, "max-fr", "max-fs", and
"profile-id". See Section 6 for their definition.
Encoding considerations: Required parameters: N/A
This media type is framed in RTP and contains binary data; see
Section 4.8 of [RFC6838].
Security considerations: Optional parameters: There are three optional parameters: max-fr,
See Section 8 of RFC xxxx. max-fs, and profile-id. See Section 6 for their definition.
[RFC Editor: Upon publication as an RFC, please replace "XXXX" Encoding considerations: This media type is framed in RTP and
with the number assigned to this document and remove this note.] contains binary data; see Section 4.8 of [RFC6838].
Interoperability considerations: Security considerations: See Section 8 of RFC 9628.
None.
Published specification: Interoperability considerations: None
VP9 bitstream format [VP9-BITSTREAM] and RFC XXXX.
[RFC Editor: Upon publication as an RFC, please replace "XXXX" Published specification: VP9 bitstream format [VP9-BITSTREAM] and
with the number assigned to this document and remove this note.] RFC 9628.
Applications which use this media type: Applications that use this media type: For example, video over IP,
For example: Video over IP, video conferencing. video conferencing.
Fragment identifier considerations: Fragment identifier considerations: N/A
N/A.
Additional information: Additional information: None
None.
Person & email address to contact for further information: Person & email address to contact for further information: Jonathan
Jonathan Lennox <jonathan.lennox@8x8.com> Lennox <jonathan.lennox@8x8.com>
Intended usage: Intended usage: COMMON
COMMON
Restrictions on usage: Restrictions on usage: This media type depends on RTP framing;
This media type depends on RTP framing, and hence is only defined hence, it is only defined for transfer via RTP [RFC3550].
for transfer via RTP [RFC3550].
Author: Author: Jonathan Lennox <jonathan.lennox@8x8.com>
Jonathan Lennox <jonathan.lennox@8x8.com>
Change controller: Change controller: IETF AVTCore Working Group delegated from the
IETF AVTCore Working Group delegated from the IESG. IESG.
8. Security Considerations 8. Security Considerations
RTP packets using the payload format defined in this specification RTP packets using the payload format defined in this specification
are subject to the security considerations discussed in the RTP are subject to the security considerations discussed in the RTP
specification [RFC3550], and in any applicable RTP profile such as specification [RFC3550], and in any applicable RTP profile such as
RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711], or RTP/ RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711], or RTP/
SAVPF [RFC5124]. However, as "Securing the RTP Protocol Framework: SAVPF [RFC5124]. However, as "Securing the RTP Framework: Why RTP
Why RTP Does Not Mandate a Single Media Security Solution" [RFC7202] Does Not Mandate a Single Media Security Solution" [RFC7202]
discusses, it is not an RTP payload format's responsibility to discusses, it is not an RTP payload format's responsibility to
discuss or mandate what solutions are used to meet the basic security discuss or mandate what solutions are used to meet the basic security
goals like confidentiality, integrity and source authenticity for RTP goals like confidentiality, integrity, and source authenticity for
in general. This responsibility lays on anyone using RTP in an RTP in general. This responsibility lies with anyone using RTP in an
application. They can find guidance on available security mechanisms application. They can find guidance on available security mechanisms
in Options for Securing RTP Sessions [RFC7201]. Applications SHOULD in "Options for Securing RTP Sessions [RFC7201]. Applications SHOULD
use one or more appropriate strong security mechanisms. The rest of use one or more appropriate strong security mechanisms.
this security consideration section discusses the security impacting
properties of the payload format itself.
Implementations of this RTP payload format need to take appropriate Implementations of this RTP payload format need to take appropriate
security considerations into account. It is extremely important for security considerations into account. It is extremely important for
the decoder to be robust against malicious or malformed payloads and the decoder to be robust against malicious or malformed payloads and
ensure that they do not cause the decoder to overrun its allocated ensure that they do not cause the decoder to overrun its allocated
memory or otherwise mis-behave. An overrun in allocated memory could memory or otherwise misbehave. An overrun in allocated memory could
lead to arbitrary code execution by an attacker. The same applies to lead to arbitrary code execution by an attacker. The same applies to
the encoder, even though problems in encoders are typically rarer. the encoder, even though problems in encoders are (typically) rarer.
This RTP payload format and its media decoder do not exhibit any This RTP payload format and its media decoder do not exhibit any
significant non-uniformity in the receiver-side computational significant non-uniformity in the receiver-side computational
complexity for packet processing, and thus are unlikely to pose a complexity for packet processing; thus, they are unlikely to pose a
denial-of-service threat due to the receipt of pathological data. denial-of-service threat due to the receipt of pathological data.
Nor does the RTP payload format contain any active content. Nor does the RTP payload format contain any active content.
9. Congestion Control 9. Congestion Control
Congestion control for RTP SHALL be used in accordance with RFC 3550 Congestion control for RTP SHALL be used in accordance with
[RFC3550], and with any applicable RTP profile; e.g., RFC 3551 [RFC3550], and with any applicable RTP profile, e.g., [RFC3551]. The
[RFC3551]. The congestion control mechanism can, in a real-time congestion control mechanism can, in a real-time encoding scenario,
encoding scenario, adapt the transmission rate by instructing the adapt the transmission rate by instructing the encoder to encode at a
encoder to encode at a certain target rate. Media aware network certain target rate. Media-aware network elements MAY use the
elements MAY use the information in the VP9 payload descriptor in information in the VP9 payload descriptor in Section 4.2 to identify
Section 4.2 to identify non-reference frames and discard them in non-reference frames and discard them in order to reduce network
order to reduce network congestion. Note that discarding of non- congestion. Note that discarding of non-reference frames cannot be
reference frames cannot be done if the stream is encrypted (because done if the stream is encrypted (because the non-reference marker is
the non-reference marker is encrypted). encrypted).
10. IANA Considerations 10. IANA Considerations
The IANA is requested to register the media type registration "video/ IANA has registered the media type registration "video/vp9" as
vp9" as specified in Section 7. The media type is also requested to specified in Section 7. The media type has also been added to the
be added to the IANA registry for "RTP Payload Format MIME types" "RTP Payload Format Media Types" <https://www.iana.org/assignments/
<http://www.iana.org/assignments/rtp-parameters>. rtp-parameters> subregistry of the "Real-Time Transport Protocol
(RTP) Paramaeters" registry as follows.
11. Acknowledgments
Alex Eleftheriadis, Yuki Ito, Won Kap Jang, Sergio Garcia Murillo,
Roi Sasson, Timothy Terriberry, Emircan Uysaler, and Thomas Volkert
commented on the development of this document and provided helpful
comments and feedback.
12. References Media Type: video
Subtype: VP9
Clock Rate (Hz): 90000
Reference: RFC 9628
12.1. Normative References 11. References
[I-D.ietf-avtext-lrr] 11.1. Normative References
Lennox, J., Hong, D., Uberti, J., Holmer, S., and M.
Flodman, "The Layer Refresh Request (LRR) RTCP Feedback
Message", Work in Progress, Internet-Draft, draft-ietf-
avtext-lrr-07, 2 July 2017,
<https://www.ietf.org/archive/id/draft-ietf-avtext-lrr-
07.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002, DOI 10.17487/RFC3264, June 2002,
<https://www.rfc-editor.org/info/rfc3264>. <https://www.rfc-editor.org/info/rfc3264>.
skipping to change at page 23, line 28 skipping to change at line 1003
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP: [RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866, Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021, DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>. <https://www.rfc-editor.org/info/rfc8866>.
[RFC9627] Lennox, J., Hong, D., Uberti, J., Holmer, S., and M.
Flodman, "The Layer Refresh Request (LRR) RTCP Feedback
Message", RFC 9627, DOI 10.17487/RFC9627, August 2024,
<https://www.rfc-editor.org/info/rfc9627>.
[VP9-BITSTREAM] [VP9-BITSTREAM]
Grange, A., de Rivaz, P., and J. Hunt, "VP9 Bitstream & Grange, A., de Rivaz, P., and J. Hunt, "VP9 Bitstream &
Decoding Process Specification", Version 0.6, 31 March Decoding Process Specification", Version 0.6, 31 March
2016, 2016,
<https://storage.googleapis.com/downloads.webmproject.org/ <https://storage.googleapis.com/downloads.webmproject.org/
docs/vp9/vp9-bitstream-specification- docs/vp9/vp9-bitstream-specification-
v0.6-20160331-draft.pdf>. v0.6-20160331-draft.pdf>.
12.2. Informative References 11.2. Informative References
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551, Video Conferences with Minimal Control", STD 65, RFC 3551,
DOI 10.17487/RFC3551, July 2003, DOI 10.17487/RFC3551, July 2003,
<https://www.rfc-editor.org/info/rfc3551>. <https://www.rfc-editor.org/info/rfc3551>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004, RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>. <https://www.rfc-editor.org/info/rfc3711>.
skipping to change at page 24, line 23 skipping to change at line 1051
[RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP [RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP
Framework: Why RTP Does Not Mandate a Single Media Framework: Why RTP Does Not Mandate a Single Media
Security Solution", RFC 7202, DOI 10.17487/RFC7202, April Security Solution", RFC 7202, DOI 10.17487/RFC7202, April
2014, <https://www.rfc-editor.org/info/rfc7202>. 2014, <https://www.rfc-editor.org/info/rfc7202>.
[RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667, [RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
DOI 10.17487/RFC7667, November 2015, DOI 10.17487/RFC7667, November 2015,
<https://www.rfc-editor.org/info/rfc7667>. <https://www.rfc-editor.org/info/rfc7667>.
Acknowledgments
Alex Eleftheriadis, Yuki Ito, Won Kap Jang, Sergio Garcia Murillo,
Roi Sasson, Timothy Terriberry, Emircan Uysaler, and Thomas Volkert
commented on the development of this document and provided helpful
feedback.
Authors' Addresses Authors' Addresses
Justin Uberti Justin Uberti
Google, Inc. Google, Inc.
747 6th Street South 747 6th Street South
Kirkland, WA 98033 Kirkland, WA 98033
United States of America United States of America
Email: justin@uberti.name Email: justin@uberti.name
Stefan Holmer Stefan Holmer
Google, Inc. Google, Inc.
Kungsbron 2 Kungsbron 2
SE-111 22 Stockholm SE-111 22 Stockholm
Sweden Sweden
Email: holmer@google.com Email: holmer@google.com
Magnus Flodman Magnus Flodman
Google, Inc. Google, Inc.
Kungsbron 2 Kungsbron 2
SE-111 22 Stockholm SE-111 22 Stockholm
Sweden Sweden
Email: mflodman@google.com Email: mflodman@google.com
Danny Hong Danny Hong
Google, Inc. Google, Inc.
1585 Charleston Road 1585 Charleston Road
Mountain View, CA 94043 Mountain View, CA 94043
United States of America United States of America
Email: dannyhong@google.com Email: dannyhong@google.com
Jonathan Lennox Jonathan Lennox
8x8, Inc. / Jitsi 8x8, Inc. / Jitsi
Jersey City, NJ 07302 Jersey City, NJ 07302
United States of America United States of America
Email: jonathan.lennox@8x8.com Email: jonathan.lennox@8x8.com
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