Internet DRAFT - draft-uberti-payload-vp9
draft-uberti-payload-vp9
Payload Working Group J. Uberti
Internet-Draft S. Holmer
Intended status: Standards Track M. Flodman
Expires: September 10, 2015 Google
J. Lennox
D. Hong
Vidyo
March 9, 2015
RTP Payload Format for VP9 Video
draft-uberti-payload-vp9-01
Abstract
This memo describes an RTP payload format for the VP9 video codec.
The payload format has wide applicability, as it supports
applications from low bit-rate peer-to-peer usage, to high bit-rate
video conferences. It includes provisions for temporal and spatial
scalability.
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
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This Internet-Draft will expire on September 10, 2015.
Copyright Notice
Copyright (c) 2015 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
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions, Definitions and Acronyms . . . . . . . . . . . . 2
3. Media Format Description . . . . . . . . . . . . . . . . . . 3
4. Payload Format . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . 4
4.2. VP9 Payload Description . . . . . . . . . . . . . . . . . 6
4.2.1. Scalability Structure (SS): . . . . . . . . . . . . . 10
4.3. VP9 Payload Header . . . . . . . . . . . . . . . . . . . 12
4.4. Frame Fragmentation . . . . . . . . . . . . . . . . . . . 12
4.5. Examples of VP9 RTP Stream . . . . . . . . . . . . . . . 12
5. Using VP9 with RPSI and SLI Feedback . . . . . . . . . . . . 12
5.1. RPSI . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2. SLI . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Payload Format Parameters . . . . . . . . . . . . . . . . . . 15
6.1. Media Type Definition . . . . . . . . . . . . . . . . . . 15
6.2. SDP Parameters . . . . . . . . . . . . . . . . . . . . . 17
6.2.1. Mapping of Media Subtype Parameters to SDP . . . . . 17
6.2.2. Offer/Answer Considerations . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Congestion Control . . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
This memo describes an RTP payload specification applicable to the
transmission of video streams encoded using the VP9 video codec
[I-D.grange-vp9-bitstream]. The format described in this document
can be used both in peer-to-peer and video conferencing applications.
TODO: VP9 description. Please see [I-D.grange-vp9-bitstream].
2. Conventions, Definitions and Acronyms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Media Format Description
The VP9 codec can maintain up to eight reference frames, of which up
to three can be referenced or updated by any new frame.
VP9 also allows a reference frame to be resampled and used as a
reference for another frame of a different resolution. This allows
internal resolution changes without requiring the use of key frames.
These features together enable an encoder to implement various forms
of coarse-grained scalability, including temporal, spatial and
quality scalability modes, as well as combinations of these, without
the need for explicit scalable coding tools.
Temporal layers define different frame rates of video; spatial and
quality layers define different and possibly dependent
representations of a single input frame. Spatial layers allow a
frame to be encoded at different resolutions, whereas quality layers
allow a frame to be encoded at the same resolution but at different
qualities (and thus with different amounts of coding error). VP9
supports quality layers as spatial layers without any resolution
changes; hereinafter, the term "spatial layer" is used to represent
both spatial and quality layers.
This payload format specification defines how such temporal and
spatial scalability layers can be described and communicated.
Layers are designed (and MUST be encoded) such that if any layer, and
all higher layers, are removed from the bitstream along any of the
two dimensions, the remaining bitstream is still correctly decodable.
For terminology, this document uses the term "layer frame" to refer
to a single encoded VP9 frame for a particular resolution/quality,
and "super frame" to refer to all the representations (layer frames)
at a single instant in time. A super frame thus consists of one or
more layer frames, encoding different spatial layers.
Within a super frame, a layer frame with spatial layer ID equal to S,
where S > 0, can depend on a frame with a lower spatial layer ID.
This "inter-layer" dependency results in additional coding gain to
the traditional "inter-picture" dependency, where a frame depends on
previously coded frame in time. For simplicity, this payload format
assumes that, within a super frame if inter-layer dependency is used,
a spatial layer S frame can only depend on spatial layer S-1 frame
when S > 0. Additionally, if inter-picture dependency is used,
spatial layer S frame is assumed to only depend on prevously coded
spatial layer S frame.
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TODO: Describe how simulcast can be supported?
Given above simplifications for inter-layer and inter-picture
dependencies, a flag (the D bit described below) is used to indicate
whether a spatial layer S frame depends on spatial layer S-1 frame.
Then a receiver only needs to know the inter-picture dependency
structure for a given spatial layer frame in order to determine its
decodability. Two modes of describing the inter-picture dependency
structure are possible: "flexible mode" and "non-flexible mode". An
encoder can only switch between the two on the very first packet of a
key frame with temporal layer ID equal to 0.
In flexible mode, each packet can contain up to 3 reference indices,
which identifies all frames referenced by the frame transmitted in
the current packet for inter-picture prediction. This (along with
the D bit) enables a receiver to identify if a frame is decodable or
not and helps it understand the temporal layer structure so that it
can drop packets as it sees fit. Since this is signaled in each
packet it makes it possible to have very flexible temporal layer
hierarchies and patterns which are changing dynamically.
In non-flexible mode, the inter-picture dependency (the reference
indices) of a group of frames (GOF) MUST be pre-specified as part of
the scalability structure (SS) data. In this mode, each packet will
have an index to refer to one of the described frames, from which the
frames referenced by the frame transmitted in the current packet for
inter-picture prediction can be identified.
The SS data can also be used to specify the resolution of each
spatial layer present in the VP9 stream.
4. Payload Format
This section describes how the encoded VP9 bitstream is encapsulated
in RTP. To handle network losses usage of RTP/AVPF [RFC4585] is
RECOMMENDED. All integer fields in the specifications are encoded as
unsigned integers in network octet order.
4.1. RTP Header Usage
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The general RTP payload format for VP9 is depicted below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| contributing source (CSRC) identifiers |
| .... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| VP9 payload descriptor (integer #bytes) |
: :
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : VP9 pyld hdr | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
+ |
: Bytes 2..N of VP9 payload :
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The VP9 payload descriptor and VP9 payload header will be described
in the next section. OPTIONAL RTP padding MUST NOT be included
unless the P bit is set.
Figure 1
Marker bit (M): MUST be set to 1 for the final packet of the highest
spatial layer frame (the final packet of the super frame), and 0
otherwise. Unless spatial scalability is in use for this super
frame, this will have the same value as the E bit described below.
Note that a MANE MUST set this value to 1 for the target spatial
layer frame when shaping out higher spatial layers.
Timestamp: The RTP timestamp indicates the time when the input frame
was sampled, at a clock rate of 90 kHz. If the input frame is
encoded with multiple layer frames, all of the layer frames of the
super frame MUST have the same timestamp.
Sequence number: The sequence numbers are monotonically increasing
in order of the encoded bitstream.
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The remaining RTP header fields are used as specified in [RFC3550].
4.2. VP9 Payload Description
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
following structure.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|I|P|L|F|B|E|V|-| (REQUIRED)
+-+-+-+-+-+-+-+-+
I: |M| PICTURE ID | (RECOMMENDED)
+-+-+-+-+-+-+-+-+
M: | EXTENDED PID | (RECOMMENDED)
+-+-+-+-+-+-+-+-+
L: | T |U| S |D| (CONDITIONALLY RECOMMENDED)
+-+-+-+-+-+-+-+-+ -\
P,F: | P_DIFF |X|N| (CONDITIONALLY RECOMMENDED) .
+-+-+-+-+-+-+-+-+ . - up to 3 times
X: |EXTENDED P_DIFF| (OPTIONAL) .
+-+-+-+-+-+-+-+-+ -/
V: | SS |
| .. |
+-+-+-+-+-+-+-+-+
Figure 2
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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
following structure.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|I|P|L|F|B|E|V|-| (REQUIRED)
+-+-+-+-+-+-+-+-+
I: |M| PICTURE ID | (RECOMMENDED)
+-+-+-+-+-+-+-+-+
M: | EXTENDED PID | (RECOMMENDED)
+-+-+-+-+-+-+-+-+
L: |GOF_IDX| S |D| (CONDITIONALLY RECOMMENDED)
+-+-+-+-+-+-+-+-+
| TL0PICIDX | (CONDITIONALLY REQUIRED)
+-+-+-+-+-+-+-+-+
V: | SS |
| .. |
+-+-+-+-+-+-+-+-+
Figure 3
I: Picture ID (PID) present. When set to one, the OPTIONAL PID MUST
be present after the mandatory first octet and specified as below.
Otherwise, PID MUST NOT be present.
P: Inter-picture predicted layer frame. When set to zero, the layer
frame does not utilize inter-picture prediction. In this case,
up-switching to current spatial layer's frame is possible from
directly lower spatial layer frame. P SHOULD also be set to zero
when encoding a layer synchronization frame in response to an LRR
[I-D.lennox-avtext-lrr].
L: Layer indices present. When set to one, the one or two octets
following the mandatory first octet and the PID (if present) is as
described by "Layer indices" below. If the F bit (described
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
to 0 (indicating non-flexible mode), then two octets are present
for the layer indices.
F: Flexible mode. F set to one indicates flexible mode and if the P
bit is also set to one, then the octets following the mandatory
first octet, the PID, and layer indices (if present) are as
described by "Reference indices" below. This MUST only be set to
one if the I bit is also set to one; if the I bit is set to zero,
then this MUST also be set to zero and ignored by receivers. The
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value of this F bit CAN ONLY CHANGE on the very first packet of a
key picture. This is a packet with the P bit equal to zero, S or
D bit (described below) equal to zero, B bit (described below)
equal to 1, and temporal layer ID equal to 0.
B: Start of a layer frame. MUST be set to 1 if the first payload
octet of the RTP packet is the beginning of a new VP9 layer frame,
and MUST NOT be 1 otherwise. Note that this layer frame might not
be the very first layer frame of a super frame.
E: End of a layer frame. MUST be set to 1 for the final RTP packet
of a VP9 layer frame, and 0 otherwise. This enables a decoder to
finish decoding the layer frame, where it otherwise may need to
wait for the next packet to explicitly know that the layer frame
is complete. Note that, if spatial scalability is in use, more
layer frames from the same super frame may follow; see the
description of the M bit above.
V: Scalability structure (SS) data present. When set to one, the
OPTIONAL SS data MUST be present in the payload descriptor.
Otherwise, the SS data MUST NOT be present.
-: Bit reserved for future use. MUST be set to zero and MUST be
ignored by the receiver.
The mandatory first octet is followed by the extension data fields
that are enabled:
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 set,
the PID field MUST contain 15 bits; otherwise, it MUST contain 7
bits. See PID below.
Picture ID (PID): Picture ID represented in 7 or 15 bits, depending
on the M bit. This is a running index of the pictures. The field
MUST be present if the I bit is equal to one. If M is set to
zero, 7 bits carry the PID; else if M is set to one, 15 bits carry
the PID. The sender may choose between 7 or 15 bits index. The
PID SHOULD start on a random number, and MUST wrap after reaching
the maximum ID. The receiver MUST NOT assume that the number of
bits in PID stay the same through the session.
Layer indices: This information is optional but recommended whenever
encoding with layers. In the flexible mode (when the F bit is set
to 1), one octet is used to specify a layer frame's temporal layer
ID (T) and spatial layer ID (S) as shown in Figure 2.
Additionally, a bit (U) is used to indcate that the current frame
is a "switching up point" frame. Another bit (D) is used to
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indicate whether inter-layer prediction is used for the current
layer frame.
In the non-flexible mode (when the F bit is set to 0), two octets
are used as depicted in Figure 3. Like the flexible mode, the
first byte contains the spatial layer ID and the D bit. Unlike
the flexible mode, instead of the T and U fields, a group of
frames index (GOF_IDX) is specified, which can be used to obtain
the values of T and U fields from the scalable structure (SS) data
described below. An additional octet to represent the temporal
layer 0 index, TL0PICIDX, is present so that all minimally
required frames can be tracked.
The T and S fields, whether obtained directly or indirectly from
the SS data, indicate the temporal and spatial layers and can help
MCUs measure bitrates per layer and can help them make a quick
decision on whether to relay a packet or not. They can also help
receivers determine what layers they are currently decoding.
T: The temporal layer ID of current frame. This field is only
present in the flexible mode (F = 1).
U: Switching up point. This bit is only present in the flexible
mode (F = 1). If this bit is set to 1 for the current frame
with temporal layer ID equal to T, then "switch up" to a higher
frame rate is possible as subsequent higher temporal layer
frames will not depend on any frame before the current frame
(in coding time) with temporal layer ID greater than T.
S: The spatial layer ID of current frame. Note that frames with
spatial layer S > 0 may be dependent on decoded spatial layer
S-1 frame within the same super frame.
D: Inter-layer dependency used. MUST be set to one if current
spatial layer S frame depends on spatial layer S-1 frame of the
same super frame. MUST only be set to zero if current spatial
layer S frame does not depend on spatial layer S-1 frame of the
same super frame. For the base layer frame with S equal to 0,
this D bit MUST be set to zero.
GOF_IDX: An index to a frame in the group of frames (GOF)
described by the SS data. This field is only present in the
non-flexible mode (F = 0). In this mode, the SS data SHOULD
have been received and the temporal characteristics of each
frame must have been speficied as group of frames in the SS
data (see the description of "Scalability structure" below).
Here, the values of the T and the U fields are derived from the
SS data. Additionally, the frame's inter-picture dependecy can
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also be obtained from the SS data. In the case no SS data has
been received or the received SS data does not specify GOF (N_G
is set to 0), then GOF_IDX MUST be ignored and the stream is
assumed to have no temporal hierarchy with both T and U equal
to 0.
TL0PICIDX: 8 bits temporal layer zero index. TL0PICIDX is only
present in the non-flexible mode (F = 0). This is a running
index for the temporal base layer frames, i.e., the frames with
temporal layer ID (TID) set to 0. If TID is larger than 0,
TL0PICIDX indicates which temporal base layer frame the current
frame depends on. TL0PICIDX MUST be incremented when TID is 0.
The index SHOULD start on a random number, and MUST restart at
0 after reaching the maximum number 255.
Reference indices: These bytes are optional, but recommended when
encoding with temporal layers in the flexible mode. When P and F
are both set to one, then at least one reference index has to be
specified as below. Additional reference indices (total of up to
3 reference indices are allowed) may be specified using the N bit
below. When either P or F is set to zero, then no reference index
is specified.
P_DIFF: The reference index specified as the relative PID from
the current frame. For example, when P_DIFF=3 on a packet
containing the frame with PID 112 means that the frame refers
back to the frame with PID 109. This calculation is done
modulo the size of the PID field, i.e., either 7 or 15 bits.
For most layer structures a 6-bit relative PID will be enough;
however, the X bit can be used to refer to older frames.
X: 1 if this layer index has an extended P_DIFF.
N: 1 if there is additional P_DIFF following the current P_DIFF.
4.2.1. Scalability Structure (SS):
The scalability structure (SS) data describes the resolution of each
layer frame within a super frame as well as the inter-picture
dependencies for a group of frames (GOF). If the VP9 payload
descriptor's "V" bit is set, the SS data is present in the position
indicated in Figure 2 and Figure 3.
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+-+-+-+-+-+-+-+-+
V: | N_S |Y| N_G |
+-+-+-+-+-+-+-+-+ -\
Y: | WIDTH | (OPTIONAL) .
+ + .
| | (OPTIONAL) .
+-+-+-+-+-+-+-+-+ . - N_S + 1 times
| HEIGHT | (OPTIONAL) .
+ + .
| | (OPTIONAL) .
+-+-+-+-+-+-+-+-+ -/ -\
N_G: | T |U| R |-|-| (OPTIONAL) .
+-+-+-+-+-+-+-+-+ -\ . - N_G + 1 times
| P_DIFF | (OPTIONAL) . - R times .
+-+-+-+-+-+-+-+-+ -/ -/
Figure 4
N_S: N_S + 1 indicates the number of spatial layers present in the
VP9 stream.
Y: Each spatial layer's frame resolution present. When set to one,
the OPTIONAL WIDTH (2 octets) and HEIGHT (2 octets) MUST be
present for each layer frame. Otherwise, the resolution MUST NOT
be present.
N_G: N_G + 1 indicates the number of frames in a GOF. If N_G is
greater than 0, then the SS data allows the inter-picture
dependency structure of the VP9 stream to be pre-declared, rather
than indicating it on the fly with every packet. If N_G is
greater than 0, then for N_G + 1 pictures in the GOF, each frame's
temporal layer ID (T), switch up point (U), and the R reference
indices (P_DIFFs) are specified.
N_G=0 indicates that either there is only one temporal layer or no
fixed inter-picture dependency information is present going
forward in the bitstream.
Note that for a given super frame, all layer frames follow the
same inter-picture dependency structure. However, the frame rate
of each spatial layer can be different from each other and this
can be controlled with the use of the D bit described above. The
specified dependency structure in the SS data MUST be for the
highest frame rate layer.
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
with P bit equal to zero, S or D bit equal to zero, B bit equal to 1,
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and temporal layer ID (TID) equal to 0. The SS data SHOULD also be
included in the first packet of the first frame in which the SS
changes. If the SS data is included in a frame with TID not equal to
0, it MUST also be repeated in the first packet of the first frame
with a lower TID, until TID equals to 0.
4.3. VP9 Payload Header
TODO: need to describe VP9 payload header.
4.4. Frame Fragmentation
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
with the RTP marker bit set. There is no mechanism for finer-grained
access to parts of a VP9 frame.
4.5. Examples of VP9 RTP Stream
TODO
5. Using VP9 with RPSI and SLI Feedback
The VP9 payload descriptor defined in Section 4.2 above contains an
optional PictureID parameter. One use of this parameter is included
to enable use of reference picture selection index (RPSI) and slice
loss indication (SLI), both defined in [RFC4585].
5.1. RPSI
TODO: Update to indicate which frame within the picture.
The reference picture selection index is a payload-specific feedback
message defined within the RTCP-based feedback format. The RPSI
message is generated by a receiver and can be used in two ways.
Either it can signal a preferred reference picture when a loss has
been detected by the decoder -- preferably then a reference that the
decoder knows is perfect -- or, it can be used as positive feedback
information to acknowledge correct decoding of certain reference
pictures. The positive feedback method is useful for VP9 used as
unicast. The use of RPSI for VP9 is preferably combined with a
special update pattern of the codec's two special reference frames --
the golden frame and the altref frame -- in which they are updated in
an alternating leapfrog fashion. When a receiver has received and
correctly decoded a golden or altref frame, and that frame had a
PictureID in the payload descriptor, the receiver can acknowledge
this simply by sending an RPSI message back to the sender. The
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message body (i.e., the "native RPSI bit string" in [RFC4585]) is
simply the PictureID of the received frame.
5.2. SLI
TODO: Update to indicate which frame within the picture.
The slice loss indication is another payload-specific feedback
message defined within the RTCP-based feedback format. The SLI
message is generated by the receiver when a loss or corruption is
detected in a frame. The format of the SLI message is as follows
[RFC4585]:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| First | Number | PictureID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5
Here, First is the macroblock address (in scan order) of the first
lost block and Number is the number of lost blocks. PictureID is the
six least significant bits of the codec-specific picture identifier
in which the loss or corruption has occurred. For VP9, this codec-
specific identifier is naturally the PictureID of the current frame,
as read from the payload descriptor. If the payload descriptor of
the current frame does not have a PictureID, the receiver MAY send
the last received PictureID+1 in the SLI message. The receiver MAY
set the First parameter to 0, and the Number parameter to the total
number of macroblocks per frame, even though only parts of the frame
is corrupted. When the sender receives an SLI message, it can make
use of the knowledge from the latest received RPSI message. Knowing
that the last golden or altref frame was successfully received, it
can encode the next frame with reference to that established
reference.
5.3. Example
TODO: this example is copied from the VP8 payload format
specification, and has not been updated for VP9. It may be
incorrect.
The use of RPSI and SLI is best illustrated in an example. In this
example, the encoder may not update the altref frame until the last
sent golden frame has been acknowledged with an RPSI message. If an
update is not received within some time, a new golden frame update is
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sent instead. Once the new golden frame is established and
acknowledged, the same rule applies when updating the altref frame.
+-------+-------------------+-------------------------+-------------+
| Event | Sender | Receiver | Established |
| | | | reference |
+-------+-------------------+-------------------------+-------------+
| 1000 | Send golden frame | | |
| | PictureID = 0 | | |
| | | | |
| | | Receive and decode | |
| | | golden frame | |
| | | | |
| 1001 | | Send RPSI(0) | |
| | | | |
| 1002 | Receive RPSI(0) | | golden |
| | | | |
| ... | (sending regular | | |
| | frames) | | |
| | | | |
| 1100 | Send altref frame | | |
| | PictureID = 100 | | |
| | | | |
| | | Altref corrupted or | golden |
| | | lost | |
| | | | |
| 1101 | | Send SLI(100) | golden |
| | | | |
| 1102 | Receive SLI(100) | | |
| | | | |
| 1103 | Send frame with | | |
| | reference to | | |
| | golden | | |
| | | | |
| | | Receive and decode | golden |
| | | frame (decoder state | |
| | | restored) | |
| | | | |
| ... | (sending regular | | |
| | frames) | | |
| | | | |
| 1200 | Send altref frame | | |
| | PictureID = 200 | | |
| | | | |
| | | Receive and decode | golden |
| | | altref frame | |
| | | | |
| 1201 | | Send RPSI(200) | |
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| | | | |
| 1202 | Receive RPSI(200) | | altref |
| | | | |
| ... | (sending regular | | |
| | frames) | | |
| | | | |
| 1300 | Send golden frame | | |
| | PictureID = 300 | | |
| | | | |
| | | Receive and decode | altref |
| | | golden frame | |
| | | | |
| 1301 | | Send RPSI(300) | altref |
| | | | |
| 1302 | RPSI lost | | |
| | | | |
| 1400 | Send golden frame | | |
| | PictureID = 400 | | |
| | | | |
| | | Receive and decode | altref |
| | | golden frame | |
| | | | |
| 1401 | | Send RPSI(400) | |
| | | | |
| 1402 | Receive RPSI(400) | | golden |
+-------+-------------------+-------------------------+-------------+
Table 1: Example signaling between sender and receiver
Note that the scheme is robust to loss of the feedback messages. If
the RPSI is lost, the sender will try to update the golden (or
altref) again after a while, without releasing the established
reference. Also, if an SLI is lost, the receiver can keep sending
SLI messages at any interval allowed by the RTCP sending timing
restrictions as specified in [RFC4585], as long as the picture is
corrupted.
6. Payload Format Parameters
This payload format has two required parameters.
6.1. Media Type Definition
This registration is done using the template defined in [RFC6838] and
following [RFC4855].
Type name: video
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Subtype name: VP9
Required parameters:
These parameters MUST be used to signal the capabilities of a
receiver implementation. These parameters MUST NOT be used for
any other purpose.
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
capable of decoding.
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 decoding.
The decoder is capable of decoding this frame size as long as
the width and height of the frame in macroblocks are less than
int(sqrt(max-fs * 8)) - for instance, a max-fs of 1200 (capable
of supporting 640x480 resolution) will support widths and
heights up to 1552 pixels (97 macroblocks).
Optional parameters: none
Encoding considerations:
This media type is framed in RTP and contains binary data; see
Section 4.8 of [RFC6838].
Security considerations: See Section 7 of RFC xxxx.
[RFC Editor: Upon publication as an RFC, please replace "XXXX"
with the number assigned to this document and remove this note.]
Interoperability considerations: None.
Published specification: VP9 bitstream format
[I-D.grange-vp9-bitstream] and RFC XXXX.
[RFC Editor: Upon publication as an RFC, please replace "XXXX"
with the number assigned to this document and remove this note.]
Applications which use this media type:
For example: Video over IP, video conferencing.
Additional information: None.
Person & email address to contact for further information:
TODO [Pick a contact]
Intended usage: COMMON
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Restrictions on usage:
This media type depends on RTP framing, and hence is only defined
for transfer via RTP [RFC3550].
Author: TODO [Pick a contact]
Change controller:
IETF Payload Working Group delegated from the IESG.
6.2. SDP Parameters
The receiver MUST ignore any fmtp parameter unspecified in this memo.
6.2.1. Mapping of Media Subtype Parameters to SDP
The media type video/VP9 string is mapped to fields in the Session
Description Protocol (SDP) [RFC4566] as follows:
o The media name in the "m=" line of SDP MUST be video.
o The encoding name in the "a=rtpmap" line of SDP MUST be VP9 (the
media subtype).
o The clock rate in the "a=rtpmap" line MUST be 90000.
o The parameters "max-fs", and "max-fr", MUST be included in the
"a=fmtp" line of SDP. These parameters are expressed as a media
subtype string, in the form of a semicolon separated list of
parameter=value pairs.
6.2.1.1. Example
An example of media representation in SDP is as follows:
m=video 49170 RTP/AVPF 98
a=rtpmap:98 VP9/90000
a=fmtp:98 max-fr=30; max-fs=3600;
6.2.2. Offer/Answer Considerations
TODO: Update this for VP9
7. Security Considerations
RTP packets using the payload format defined in this specification
are subject to the security considerations discussed in the RTP
specification [RFC3550], and in any applicable RTP profile. The main
security considerations for the RTP packet carrying the RTP payload
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format defined within this memo are confidentiality, integrity and
source authenticity. Confidentiality is achieved by encryption of
the RTP payload. Integrity of the RTP packets through suitable
cryptographic integrity protection mechanism. Cryptographic system
may also allow the authentication of the source of the payload. A
suitable security mechanism for this RTP payload format should
provide confidentiality, integrity protection and at least source
authentication capable of determining if an RTP packet is from a
member of the RTP session or not. Note that the appropriate
mechanism to provide security to RTP and payloads following this memo
may vary. It is dependent on the application, the transport, and the
signaling protocol employed. Therefore a single mechanism is not
sufficient, although if suitable the usage of SRTP [RFC3711] is
recommended. This RTP payload format and its media decoder do not
exhibit any significant non-uniformity in the receiver-side
computational complexity for packet processing, and thus are unlikely
to pose a denial-of-service threat due to the receipt of pathological
data. Nor does the RTP payload format contain any active content.
8. Congestion Control
Congestion control for RTP SHALL be used in accordance with RFC 3550
[RFC3550], and with any applicable RTP profile; e.g., RFC 3551
[RFC3551]. The congestion control mechanism can, in a real-time
encoding scenario, adapt the transmission rate by instructing the
encoder to encode at a certain target rate. Media aware network
elements MAY use the information in the VP9 payload descriptor in
Section 4.2 to identify non-reference frames and discard them in
order to reduce network congestion. Note that discarding of non-
reference frames cannot be done if the stream is encrypted (because
the non-reference marker is encrypted).
9. IANA Considerations
The IANA is requested to register the following values:
- Media type registration as described in Section 6.1.
10. References
[I-D.grange-vp9-bitstream]
Grange, A. and H. Alvestrand, "A VP9 Bitstream Overview",
draft-grange-vp9-bitstream-00 (work in progress), February
2013.
[I-D.lennox-avtext-lrr]
Lennox, J., Uberti, J., Holmer, S., and M. Flodman, "The
Layer Refresh Request (LRR) RTCP Feedback MessageVideo",
draft-lennox-avtext-lrr-00 (work in progress), March 2015.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July
2006.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, RFC
6838, January 2013.
Authors' Addresses
Justin Uberti
Google, Inc.
747 6th Street South
Kirkland, WA 98033
USA
Email: justin@uberti.name
Stefan Holmer
Google, Inc.
Kungsbron 2
Stockholm 111 22
Sweden
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Magnus Flodman
Google, Inc.
Kungsbron 2
Stockholm 111 22
Sweden
Jonathan Lennox
Vidyo, Inc.
433 Hackensack Avenue
Seventh Floor
Hackensack, NJ 07601
US
Email: jonathan@vidyo.com
Danny Hong
Vidyo, Inc.
433 Hackensack Avenue
Seventh Floor
Hackensack, NJ 07601
US
Email: danny@vidyo.com
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