Internet Engineering Task Force (IETF) P. Westin
Request for Comments: 7741 H. Lundin
Category: Standards Track Google
ISSN: 2070-1721 M. Glover
Twitter
J. Uberti
F. Galligan
Google
March 2016
Internet Engineering Task Force (IETF) P. Westin
Request for Comments: 7741 H. Lundin
Category: Standards Track Google
ISSN: 2070-1721 M. Glover
Twitter
J. Uberti
F. Galligan
Google
March 2016
RTP Payload Format for VP8 Video
VP8视频的RTP有效负载格式
Abstract
摘要
This memo describes an RTP payload format for the VP8 video codec. The payload format has wide applicability, as it supports applications from low-bitrate peer-to-peer usage to high-bitrate video conferences.
本备忘录描述了VP8视频编解码器的RTP有效负载格式。有效负载格式具有广泛的适用性，因为它支持从低比特率对等使用到高比特率视频会议的应用。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7741.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc7741.
Copyright Notice
版权公告
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2016 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include 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.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction ....................................................3
2. Conventions, Definitions, and Abbreviations .....................3
3. Media Format Description ........................................4
4. Payload Format ..................................................5
4.1. RTP Header Usage ...........................................6
4.2. VP8 Payload Descriptor .....................................7
4.3. VP8 Payload Header ........................................11
4.4. Aggregated and Fragmented Payloads ........................12
4.5. Example Algorithms ........................................13
4.5.1. Frame Reconstruction Algorithm .....................13
4.5.2. Partition Reconstruction Algorithm .................13
4.6. Examples of VP8 RTP Stream ................................14
4.6.1. Key Frame in a Single RTP Packet ...................14
4.6.2. Non-discardable VP8 Interframe in a Single
RTP Packet; No PictureID ...........................14
4.6.3. VP8 Partitions in Separate RTP Packets .............15
4.6.4. VP8 Frame Fragmented across RTP Packets ............16
4.6.5. VP8 Frame with Long PictureID ......................18
5. Using VP8 with RPSI and SLI Feedback ...........................18
5.1. RPSI ......................................................18
5.2. SLI .......................................................19
5.3. Example ...................................................19
6. Payload Format Parameters ......................................21
6.1. Media Type Definition .....................................21
6.2. SDP Parameters ............................................23
6.2.1. Mapping of Media Subtype Parameters to SDP .........23
6.2.2. Offer/Answer Considerations ........................23
7. Security Considerations ........................................24
8. Congestion Control .............................................24
9. IANA Considerations ............................................24
10. References ....................................................25
10.1. Normative References .....................................25
10.2. Informative References ...................................26
Authors' Addresses ................................................28
1. Introduction ....................................................3
2. Conventions, Definitions, and Abbreviations .....................3
3. Media Format Description ........................................4
4. Payload Format ..................................................5
4.1. RTP Header Usage ...........................................6
4.2. VP8 Payload Descriptor .....................................7
4.3. VP8 Payload Header ........................................11
4.4. Aggregated and Fragmented Payloads ........................12
4.5. Example Algorithms ........................................13
4.5.1. Frame Reconstruction Algorithm .....................13
4.5.2. Partition Reconstruction Algorithm .................13
4.6. Examples of VP8 RTP Stream ................................14
4.6.1. Key Frame in a Single RTP Packet ...................14
4.6.2. Non-discardable VP8 Interframe in a Single
RTP Packet; No PictureID ...........................14
4.6.3. VP8 Partitions in Separate RTP Packets .............15
4.6.4. VP8 Frame Fragmented across RTP Packets ............16
4.6.5. VP8 Frame with Long PictureID ......................18
5. Using VP8 with RPSI and SLI Feedback ...........................18
5.1. RPSI ......................................................18
5.2. SLI .......................................................19
5.3. Example ...................................................19
6. Payload Format Parameters ......................................21
6.1. Media Type Definition .....................................21
6.2. SDP Parameters ............................................23
6.2.1. Mapping of Media Subtype Parameters to SDP .........23
6.2.2. Offer/Answer Considerations ........................23
7. Security Considerations ........................................24
8. Congestion Control .............................................24
9. IANA Considerations ............................................24
10. References ....................................................25
10.1. Normative References .....................................25
10.2. Informative References ...................................26
Authors' Addresses ................................................28
This memo describes an RTP payload specification applicable to the transmission of video streams encoded using the VP8 video codec [RFC6386]. The format described in this document can be used both in peer-to-peer and video-conferencing applications.
本备忘录描述了适用于使用VP8视频编解码器[RFC6386]编码的视频流传输的RTP有效负载规范。本文档中描述的格式可用于对等和视频会议应用程序。
VP8 is based on the decomposition of frames into square sub-blocks of pixels known as "macroblocks" (see Section 2 of [RFC6386]). Prediction of such sub-blocks using previously constructed blocks, and adjustment of such predictions (as well as synthesis of unpredicted blocks) is done using a discrete cosine transform (hereafter abbreviated as DCT). In one special case, however, VP8 uses a "Walsh-Hadamard" transform (hereafter abbreviated as WHT) instead of a DCT. An encoded VP8 frame is divided into two or more partitions, as described in [RFC6386]. The first partition (prediction or mode) contains prediction mode parameters and motion vectors for all macroblocks. The remaining partitions all contain the quantized DCT/WHT coefficients for the residuals. There can be 1, 2, 4, or 8 DCT/WHT partitions per frame, depending on encoder settings.
VP8基于将帧分解为称为“宏块”的像素方子块（见[RFC6386]第2节）。使用先前构造的块来预测这样的子块，并且使用离散余弦变换（以下简称为DCT）来调整这样的预测（以及合成不可预测的块）。然而，在一种特殊情况下，VP8使用“沃尔什-哈达玛”变换（以下简称WHT）代替DCT。编码的VP8帧被划分为两个或多个分区，如[RFC6386]所述。第一分区（预测或模式）包含所有宏块的预测模式参数和运动矢量。其余分区都包含残差的量化DCT/WHT系数。根据编码器设置，每帧可以有1、2、4或8个DCT/WHT分区。
In summary, the payload format described in this document enables a number of features in VP8, including:
总之，本文档中描述的有效负载格式支持VP8中的许多功能，包括：
o Taking partition boundaries into consideration, to improve loss robustness and facilitate efficient packet-loss concealment at the decoder.
o 考虑到分区边界，以提高丢失鲁棒性并促进解码器处的有效分组丢失隐藏。
o Temporal scalability.
o 时间可伸缩性。
o Advanced use of reference frames to enable efficient error recovery.
o 高级使用参考帧以实现高效的错误恢复。
o Marking of frames that have no impact on the decoding of any other frame, so that these non-reference frames can be discarded in a server or media-aware network element if needed.
o 标记对任何其他帧的解码没有影响的帧，以便在需要时可以在服务器或媒体感知网络元件中丢弃这些非参考帧。
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].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
This document uses the definitions of [RFC6386]. In particular, the following terms are used.
本文件使用[RFC6386]的定义。具体而言，使用以下术语。
Key frames: Frames that are decoded without reference to any other frame in a sequence (also called intraframes and I-frames).
关键帧：在不参考序列中任何其他帧的情况下解码的帧（也称为帧内帧和I帧）。
Interframes: Frames that are encoded with reference to prior frames, specifically all prior frames up to and including the most recent key frame (also called prediction frames and P-frames).
帧间：参照先前帧编码的帧，特别是最近关键帧（也称为预测帧和P帧）之前的所有先前帧。
Golden and altref frames: alternate prediction frames. Blocks in an interframe may be predicted using blocks in the immediately previous frame as well as the most recent golden frame or altref frame. Every key frame is automatically golden and altref, and any interframe may optionally replace the most recent golden or altref frame.
Golden和altref帧：交替预测帧。可以使用前一帧中的块以及最近的黄金帧或altref帧中的块来预测帧间中的块。每个关键帧自动为golden和altref，任何帧间帧都可以选择替换最近的golden或altref帧。
Macroblock: a square array of pixels whose Y (luminance) dimensions are 16x16 pixels and whose U and V (chrominance) dimensions are 8x8 pixels.
宏块：Y（亮度）尺寸为16x16像素，U和V（色度）尺寸为8x8像素的正方形像素阵列。
Two definitions from [RFC4585] are also used in this document.
本文件中还使用了[RFC4585]中的两个定义。
RPSI: Reference picture selection indication. A feedback message to let the encoder know that the decoder has correctly decoded a certain frame.
RPSI：参考图片选择指示。一种反馈消息，用于让编码器知道解码器已正确解码特定帧。
SLI: Slice loss indication. A feedback message to let a decoder inform an encoder that it has detected the loss or corruption of one or several macroblocks.
SLI：切片丢失指示。一种反馈信息，让解码器通知编码器它已检测到一个或多个宏块的丢失或损坏。
The VP8 codec uses three different reference frames for interframe prediction: the previous frame, the golden frame, and the altref frame. Blocks in an interframe may be predicted using blocks in the immediately previous frame as well as the most recent golden frame or altref frame. Every key frame is automatically golden and altref, and any interframe may optionally replace the most recent golden or altref frame. Golden frames and altref frames may also be used to increase the tolerance to dropped frames. The payload specification in this memo has elements that enable advanced use of the reference frames, e.g., for improved loss robustness.
VP8编解码器使用三种不同的参考帧进行帧间预测：前一帧、黄金帧和altref帧。可以使用前一帧中的块以及最近的黄金帧或altref帧中的块来预测帧间中的块。每个关键帧自动为golden和altref，任何帧间帧都可以选择替换最近的golden或altref帧。金色框架和altref框架也可用于增加对掉落框架的公差。本备忘录中的有效载荷规范包含能够高级使用参考帧的元素，例如，用于提高损失鲁棒性。
One specific use case of the three reference frame types is temporal scalability. By setting up the reference hierarchy in the appropriate way, up to five temporal layers can be encoded. (How to set up the reference hierarchy for temporal scalability is not within
三种参考帧类型的一个特定用例是时间可伸缩性。通过以适当的方式设置参考层次结构，最多可以对五个时间层进行编码。（如何为时间可伸缩性设置参考层次结构不在
the scope of this memo.) Support for temporal scalability is provided by the optional TL0PICIDX and TID/Y/KEYIDX fields described in Section 4.2. For a general description of temporal scalability for video coding, see [Sch07].
第4.2节中描述的可选TL0PICIDX和TID/Y/KEYIDX字段提供了对时间可伸缩性的支持。有关视频编码的时间可伸缩性的一般说明，请参见[Sch07]。
Another property of the VP8 codec is that it applies data partitioning to the encoded data. Thus, an encoded VP8 frame can be divided into two or more partitions, as described in "VP8 Data Format and Decoding Guide" [RFC6386]. The first partition (prediction or mode) contains prediction mode parameters and motion vectors for all macroblocks. The remaining partitions all contain the transform coefficients for the residuals. The first partition is decodable without the remaining residual partitions. The subsequent partitions may be useful even if some part of the frame is lost. Accordingly, this document RECOMMENDS that the frame be packetized by the sender with each data partition in a separate packet or packets. This may be beneficial for decoder-side error concealment, and the payload format described in Section 4 provides fields that allow the partitions to be identified even if the first partition is not available. The sender can, alternatively, aggregate the data partitions into a single data stream and, optionally, split it into several packets without consideration of the partition boundaries. The receiver can use the length information in the first partition to identify the partitions during decoding.
VP8编解码器的另一个特性是将数据分区应用于编码数据。因此，编码的VP8帧可以被划分为两个或多个分区，如“VP8数据格式和解码指南”[RFC6386]中所述。第一分区（预测或模式）包含所有宏块的预测模式参数和运动矢量。其余的分区都包含残差的变换系数。第一个分区是可解码的，没有剩余的分区。即使部分帧丢失，后续分区也可能有用。因此，本文件建议发送方将帧打包，每个数据分区在一个或多个单独的数据包中。这可能有利于解码器侧错误隐藏，并且第4节中描述的有效载荷格式提供了允许识别分区的字段，即使第一分区不可用。或者，发送方可以将数据分区聚合为单个数据流，并且可以选择将其拆分为多个分组，而不考虑分区边界。接收机可以在解码期间使用第一分区中的长度信息来识别分区。
The format specification is described in Section 4. In Section 5, a method to acknowledge receipt of reference frames using RTCP techniques is described.
格式规范见第4节。在第5节中，描述了使用RTCP技术确认参考帧接收的方法。
The payload partitioning and the acknowledging method both serve as motivation for three of the fields included in the payload format: the "PID", "1st partition size", and "PictureID" fields. The ability to encode a temporally scalable stream motivates the "TL0PICIDX" and "TID" fields.
有效负载分区和确认方法都是有效负载格式中包含的三个字段的动机：“PID”、“第一分区大小”和“PictureID”字段。对时间可伸缩流进行编码的能力激发了“TL0PICIDX”和“TID”字段。
This section describes how the encoded VP8 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.
本节描述编码的VP8比特流如何封装在RTP中。为了处理网络损耗，建议使用RTP/AVPF[RFC4585]。规范中的所有整数字段均按网络八位字节顺序编码为无符号整数。
The general RTP payload format for VP8 is depicted below.
VP8的通用RTP有效负载格式如下所示。
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 |
| .... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| VP8 payload descriptor (integer #octets) |
: :
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : VP8 payload header (3 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VP8 pyld hdr : |
+-+-+-+-+-+-+-+-+ |
: Octets 4..N of VP8 payload :
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 |
| .... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| VP8 payload descriptor (integer #octets) |
: :
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : VP8 payload header (3 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VP8 pyld hdr : |
+-+-+-+-+-+-+-+-+ |
: Octets 4..N of VP8 payload :
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| : OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The VP8 payload descriptor and VP8 payload header will be described in Sections 4.2 and 4.3. OPTIONAL RTP padding MUST NOT be included unless the P bit is set. The figure specifically shows the format for the first packet in a frame. Subsequent packets will not contain the VP8 payload header and will have later octets in the frame payload.
VP8有效负载描述符和VP8有效负载标头将在第4.2节和第4.3节中描述。除非设置了P位，否则不得包括可选RTP填充。该图具体显示了帧中第一个数据包的格式。后续数据包将不包含VP8有效负载报头，并且将在帧有效负载中具有稍后的八位字节。
Figure 1
图1
Marker bit (M): MUST be set for the very last packet of each encoded frame in line with the normal use of the M bit in video formats. This enables a decoder to finish decoding the picture, where it otherwise may need to wait for the next packet to explicitly know that the frame is complete.
标记位（M）：必须按照视频格式中M位的正常使用，为每个编码帧的最后一个数据包设置标记位（M）。这使得解码器能够完成对图片的解码，否则它可能需要等待下一个分组明确地知道帧已完成。
Payload type (PT): The assignment of an RTP payload type for this packet format is outside the scope of this document and will not be specified here.
有效负载类型（PT）：此数据包格式的RTP有效负载类型的分配不在本文档的范围内，此处将不指定。
Timestamp: The RTP timestamp indicates the time when the frame was sampled. The granularity of the clock is 90 kHz, so a delta of 1 represents 1/90,000 of a second.
时间戳：RTP时间戳表示对帧进行采样的时间。时钟的粒度为90 kHz，因此1的增量表示1/90000秒。
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 [RFC3550].
剩余的RTP固定头字段（V、P、X、CC、序列号、SSRC和CSC标识符）按照[RFC3550]第5.1节的规定使用。
The first octets after the RTP header are the VP8 payload descriptor, with the following structure. The single-octet version of the PictureID is illustrated to the left (M bit set to 0), while the dual-octet version (M bit set to 1) is shown to the right.
RTP报头之后的第一个八位字节是VP8有效负载描述符，其结构如下。图片ID的单八位版本显示在左侧（M位设置为0），而双八位版本（M位设置为1）显示在右侧。
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|X|R|N|S|R| PID | (REQUIRED) |X|R|N|S|R| PID | (REQUIRED)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
X: |I|L|T|K| RSV | (OPTIONAL) X: |I|L|T|K| RSV | (OPTIONAL)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
I: |M| PictureID | (OPTIONAL) I: |M| PictureID | (OPTIONAL)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
L: | TL0PICIDX | (OPTIONAL) | PictureID |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
T/K: |TID|Y| KEYIDX | (OPTIONAL) L: | TL0PICIDX | (OPTIONAL)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
T/K: |TID|Y| KEYIDX | (OPTIONAL)
+-+-+-+-+-+-+-+-+
Figure 2
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|X|R|N|S|R| PID | (REQUIRED) |X|R|N|S|R| PID | (REQUIRED)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
X: |I|L|T|K| RSV | (OPTIONAL) X: |I|L|T|K| RSV | (OPTIONAL)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
I: |M| PictureID | (OPTIONAL) I: |M| PictureID | (OPTIONAL)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
L: | TL0PICIDX | (OPTIONAL) | PictureID |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
T/K: |TID|Y| KEYIDX | (OPTIONAL) L: | TL0PICIDX | (OPTIONAL)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
T/K: |TID|Y| KEYIDX | (OPTIONAL)
+-+-+-+-+-+-+-+-+
Figure 2
X: Extended control bits present. When set to 1, the extension octet MUST be provided immediately after the mandatory first octet. If the bit is zero, all optional fields MUST be omitted. Note: this X bit is not to be confused with the X bit in the RTP header.
X：存在扩展控制位。设置为1时，必须在强制的第一个八位字节之后立即提供扩展八位字节。如果位为零，则必须省略所有可选字段。注意：此X位不能与RTP标头中的X位混淆。
R: Bit reserved for future use. MUST be set to 0 and MUST be ignored by the receiver.
R：保留位供将来使用。必须设置为0，并且必须被接收器忽略。
N: Non-reference frame. When set to 1, the frame can be discarded without affecting any other future or past frames. If the reference status of the frame is unknown, this bit SHOULD be set to 0 to avoid discarding frames needed for reference.
N：非参考系。设置为1时，可以丢弃帧，而不会影响任何其他未来或过去的帧。如果帧的参考状态未知，则该位应设置为0，以避免丢弃参考所需的帧。
Informative note: This document does not describe how to determine if an encoded frame is non-reference. The reference status of an encoded frame is preferably provided from the encoder implementation.
资料性说明：本文档不描述如何确定编码帧是否为非参考帧。编码帧的参考状态优选地由编码器实现提供。
S: Start of VP8 partition. SHOULD be set to 1 when the first payload octet of the RTP packet is the beginning of a new VP8 partition, and MUST NOT be 1 otherwise. The S bit MUST be set to 1 for the first packet of each encoded frame.
S：VP8分区的开始。当RTP数据包的第一个有效负载八位组是新VP8分区的开始时，应设置为1，否则不得设置为1。对于每个编码帧的第一个数据包，S位必须设置为1。
PID: Partition index. Denotes to which VP8 partition the first payload octet of the packet belongs. The first VP8 partition (containing modes and motion vectors) MUST be labeled with PID = 0. PID SHOULD be incremented by 1 for each subsequent partition, but it MAY be kept at 0 for all packets. PID cannot be larger than 7. If more than one packet in an encoded frame contains the same PID, the S bit MUST NOT be set for any packet other than the first packet with that PID.
PID：分区索引。表示数据包的第一个有效负载八位组所属的VP8分区。第一个VP8分区（包含模式和运动矢量）必须标记为PID=0。对于每个后续分区，PID应该增加1，但对于所有数据包，它可以保持为0。PID不能大于7。如果编码帧中的多个数据包包含相同的PID，则除了具有该PID的第一个数据包外，不得为任何数据包设置S位。
When the X bit is set to 1 in the first octet, the Extended Control Bits field octet MUST be provided as the second octet. If the X bit is 0, the Extended Control Bits field octet MUST NOT be present, and no extensions (I, L, T, or K) are permitted.
当第一个八位字节中的X位设置为1时，必须提供扩展控制位字段八位字节作为第二个八位字节。如果X位为0，则扩展控制位字段八位字节不得存在，并且不允许扩展（I、L、T或K）。
I: PictureID present. When set to 1, the PictureID MUST be present after the extension bit field and specified as below. Otherwise, PictureID MUST NOT be present.
I:我现在就去。当设置为1时，PictureID必须出现在扩展位字段之后，并按以下方式指定。否则，PictureID不得出现。
L: TL0PICIDX present. When set to 1, the TL0PICIDX MUST be present and specified as below, and the T bit MUST be set to 1. Otherwise, TL0PICIDX MUST NOT be present.
L:TL0PICIDX存在。当设置为1时，TL0PICIDX必须存在并按如下所示指定，T位必须设置为1。否则，TL0PICIDX必须不存在。
T: TID present. When set to 1, the TID/Y/KEYIDX octet MUST be present. The TID|Y part of the octet MUST be specified as below. If K (below) is set to 1 but T is set to 0, the TID/Y/KEYIDX octet MUST be present, but the TID field MUST be ignored. If neither T nor K is set to 1, the TID/Y/KEYIDX octet MUST NOT be present.
T:我现在就去。设置为1时，必须存在TID/Y/KEYIDX八位字节。八位字节的TID | Y部分必须指定如下。如果K（以下）设置为1，但T设置为0，则必须存在TID/Y/KEYIDX八位字节，但必须忽略TID字段。如果T和K均未设置为1，则TID/Y/KEYIDX八位字节不得存在。
K: KEYIDX present. When set to 1, the TID/Y/KEYIDX octet MUST be present. The KEYIDX part of the octet MUST be specified as below. If T (above) is set to 1 but K is set to 0, the TID/Y/KEYIDX octet MUST be present, but the KEYIDX field MUST be ignored. If neither T nor K is set to 1, the TID/Y/KEYIDX octet MUST NOT be present.
K:KEYIDX现在。设置为1时，必须存在TID/Y/KEYIDX八位字节。八位字节的KEYIDX部分必须指定如下。如果T（以上）设置为1，但K设置为0，则必须存在TID/Y/KEYIDX八位字节，但必须忽略KEYIDX字段。如果T和K均未设置为1，则TID/Y/KEYIDX八位字节不得存在。
RSV: Bits reserved for future use. MUST be set to 0 and MUST be ignored by the receiver.
RSV：为将来使用而保留的位。必须设置为0，并且必须被接收器忽略。
After the extension bit field follow the extension data fields that are enabled.
在扩展位字段之后，跟随启用的扩展数据字段。
The PictureID extension: If the I bit is set to 1, the PictureID extension field MUST be present, and it MUST NOT be present otherwise. The field consists of two parts:
PictureID扩展：如果I位设置为1，则PictureID扩展字段必须存在，否则不能存在。该字段由两部分组成：
M: The most significant bit of the first octet is an extension flag. If M is set, the remainder of the PictureID field MUST contain 15 bits, else it MUST contain 7 bits. Note: this M bit is not to be confused with the M bit in the RTP header.
M：第一个八位字节的最高有效位是扩展标志。如果设置了M，则PictureID字段的其余部分必须包含15位，否则必须包含7位。注意：此M位不能与RTP标头中的M位混淆。
PictureID: 7 or 15 bits (shown left and right, respectively, in Figure 2) not including the M bit. This is a running index of the frames, which MAY start at a random value, MUST increase by 1 for each subsequent frame, and MUST wrap to 0 after reaching the maximum ID (all bits set). The 7 or 15 bits of the PictureID go from most significant to least significant, beginning with the first bit after the M bit. The sender chooses a 7- or 15-bit index and sets the M bit accordingly. The receiver MUST NOT assume that the number of bits in PictureID stays the same through the session. Having sent a 7-bit PictureID with all bits set to 1, the sender may either wrap the PictureID to 0 or extend to 15 bits and continue incrementing.
PictureID:7或15位（图2中分别显示为左侧和右侧），不包括M位。这是帧的运行索引，可以从随机值开始，对于每个后续帧必须增加1，并且在达到最大ID（所有位设置）后必须换行为0。PictureID的7或15位从最高有效到最低有效，从M位后的第一位开始。发送方选择7位或15位索引，并相应地设置M位。接收方不得假设PictureID中的位数在整个会话中保持不变。发送7位PictureID且所有位均设置为1后，发送方可以将PictureID包装为0或扩展为15位并继续递增。
The TL0PICIDX extension: If the L bit is set to 1, the TL0PICIDX extension field MUST be present, and it MUST NOT be present otherwise. The field consists of one part:
TL0PICIDX扩展名：如果L位设置为1，则TL0PICIDX扩展名字段必须存在，否则不能存在。该字段由一部分组成：
TL0PICIDX: 8 bits temporal level zero index. TL0PICIDX is a running index for the temporal base layer frames, i.e., the frames with TID set to 0. If TID is larger than 0, TL0PICIDX indicates on which base-layer frame the current image depends. TL0PICIDX MUST be incremented when TID is 0. The index MAY start at a random value, and it MUST wrap to 0 after reaching the maximum number 255. Use of TL0PICIDX depends on the presence of TID. Therefore, it is RECOMMENDED that the TID be used whenever TL0PICIDX is.
TL0PICIDX:8位时间级零索引。TL0PICIDX是临时基本层帧的运行索引，即TID设置为0的帧。如果TID大于0，则TL0PICIDX指示当前图像所依赖的基本层帧。当TID为0时，TL0PICIDX必须递增。索引可以从随机值开始，在达到最大值255后必须换行为0。TL0PICIDX的使用取决于TID的存在。因此，建议在安装TL0PICIDX时使用TID。
The TID/Y/KEYIDX extension: If either of the T or K bits are set to 1, the TID/Y/KEYIDX extension field MUST be present. It MUST NOT be present if both T and K are zero. The field consists of three parts:
TID/Y/KEYIDX扩展：如果T或K位中的任何一位设置为1，则必须存在TID/Y/KEYIDX扩展字段。如果T和K都为零，则它不得存在。该字段由三部分组成：
TID: 2 bits temporal-layer index. The TID field MUST be ignored by the receiver when the T bit is set equal to 0. The TID field indicates which temporal layer the packet represents.
TID：2位时间层索引。当T位设置为0时，接收器必须忽略TID字段。TID字段指示数据包所代表的时间层。
The lowest layer, i.e., the base layer, MUST have the TID set to 0. Higher layers SHOULD increment the TID according to their position in the layer hierarchy.
最低层（即基层）的TID必须设置为0。较高层应根据其在层层次结构中的位置增加TID。
Y: 1 layer sync bit. The Y bit SHOULD be set to 1 if the current frame depends only on the base layer (TID = 0) frame with TL0PICIDX equal to that of the current frame. The Y bit MUST be set to 0 if the current frame depends on any other frame than the base layer (TID = 0) frame with TL0PICIDX equal to that of the current frame. Additionally, the Y bit MUST be set to 0 if any frame following the current frame depends on a non-base-layer frame older than the base-layer frame with TL0PICIDX equal to that of the current frame. If the Y bit is set when the T bit is equal to 0, the current frame MUST only depend on a past base-layer (TID=0) key frame as signaled by a change in the KEYIDX field. Additionally, this frame MUST NOT depend on any of the three codec buffers (as defined by [RFC6386]) that have been updated since the last time the KEYIDX field was changed.
Y:1层同步位。如果当前帧仅依赖于TL0PICIDX等于当前帧的基本层（TID=0）帧，则Y位应设置为1。如果当前帧依赖于TL0PICIDX等于当前帧的基本层（TID=0）帧以外的任何其他帧，则Y位必须设置为0。此外，如果当前帧后面的任何帧依赖于TL0PICIDX等于当前帧TL0PICIDX的早于基础层帧的非基础层帧，则Y位必须设置为0。如果在T位等于0时设置Y位，则当前帧必须仅依赖于过去的基本层（TID=0）关键帧，如KEYIDX字段中的更改所示。此外，此帧不得依赖于自上次更改KEYIDX字段以来已更新的三个编解码器缓冲区（由[RFC6386]定义）中的任何一个。
Informative note: This document does not describe how to determine the dependency status for a frame; this information is preferably provided from the encoder implementation. In the case of unknown status, the Y bit can safely be set to 0.
资料性说明：本文档不描述如何确定框架的依赖状态；该信息优选地从编码器实现提供。在未知状态的情况下，Y位可以安全地设置为0。
KEYIDX: 5 bits temporal key frame index. The KEYIDX field MUST be ignored by the receiver when the K bit is set equal to 0. The KEYIDX field is a running index for key frames. KEYIDX MAY start at a random value, and it MUST wrap to 0 after reaching the maximum number 31. When in use, the KEYIDX SHOULD be present for both key frames and interframes. The sender MUST increment KEYIDX for key frames that convey parameter updates critical to the interpretation of subsequent frames, and it SHOULD leave the KEYIDX unchanged for key frames that do not contain these critical updates. If the KEYIDX is present, a receiver SHOULD NOT decode an interframe if it has not received and decoded a key frame with the same KEYIDX after the last KEYIDX wraparound.
KEYIDX:5位时态关键帧索引。当K位设置为0时，接收器必须忽略KEYIDX字段。KEYIDX字段是关键帧的运行索引。KEYIDX可以从随机值开始，在达到最大值31后必须换行为0。使用时，关键帧和帧间都应显示KEYIDX。对于传递对后续帧的解释至关重要的参数更新的关键帧，发送方必须增加KEYIDX，对于不包含这些关键更新的关键帧，发送方应保持KEYIDX不变。如果存在KEYIDX，则如果在最后一次KEYIDX环绕后未接收并解码具有相同KEYIDX的关键帧，则接收器不应解码帧间。
Informative note: This document does not describe how to determine if a key frame updates critical parameters; this information is preferably provided from the encoder implementation. A sender that does not have this information may either omit the KEYIDX field (set K equal to 0) or increment the KEYIDX on every key frame. The benefit with the latter is that any key-frame loss will be detected by the receiver, which can signal for re-transmission or request a new key frame.
资料性说明：本文件不描述如何确定关键帧是否更新关键参数；该信息优选地从编码器实现提供。没有此信息的发送方可以省略KEYIDX字段（将K设置为0）或在每个关键帧上增加KEYIDX。后者的好处是，任何关键帧丢失都将被接收器检测到，接收器可以发出信号重新传输或请求新的关键帧。
Informative note: Implementations doing splicing of VP8 streams will have to make sure the rules for incrementing TL0PICIDX and KEYIDX are obeyed across the splice. This will likely require rewriting values of TL0PICIDX and KEYIDX after the splice.
资料性说明：执行VP8流拼接的实现必须确保拼接过程中遵守递增TL0PICIDX和KEYIDX的规则。这可能需要在拼接后重写TL0PICIDX和KEYIDX的值。
The beginning of an encoded VP8 frame is referred to as an "uncompressed data chunk" in Section 9.1 of [RFC6386], and it also serves as a payload header in this RTP format. The codec bitstream format specifies two different variants of the uncompressed data chunk: a 3-octet version for interframes and a 10-octet version for key frames. The first 3 octets are common to both variants. In the case of a key frame, the remaining 7 octets are considered to be part of the remaining payload in this RTP format. Note that the header is present only in packets that have the S bit equal to one and the PID equal to zero in the payload descriptor. Subsequent packets for the same frame do not carry the payload header.
编码的VP8帧的开头在[RFC6386]第9.1节中称为“未压缩数据块”，它也用作此RTP格式中的有效负载头。编解码器比特流格式指定未压缩数据块的两种不同变体：用于帧间的3个八位字节版本和用于关键帧的10个八位字节版本。前3个八位组是两种变体的共同点。在关键帧的情况下，剩余的7个八位字节被认为是该RTP格式中剩余有效载荷的一部分。注意，报头仅存在于有效负载描述符中S位等于1且PID等于零的数据包中。同一帧的后续数据包不携带有效负载报头。
The length of the first partition can always be obtained from the first partition-size parameter in the VP8 payload header. The VP8 bitstream format [RFC6386] specifies that if multiple DCT/WHT partitions are produced, the location of each partition start is found at the end of the first (prediction or mode) partition. In this RTP payload specification, the location offsets are considered to be part of the first partition.
第一个分区的长度始终可以从VP8有效负载头中的第一个分区大小参数获得。VP8比特流格式[RFC6386]规定，如果生成多个DCT/WHT分区，则在第一个（预测或模式）分区的末尾找到每个分区的起始位置。在该RTP有效负载规范中，位置偏移被认为是第一分区的一部分。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|Size0|H| VER |P|
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Octets 4..N of|
| VP8 payload |
: :
+-+-+-+-+-+-+-+-+
| OPTIONAL RTP |
| padding |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|Size0|H| VER |P|
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Octets 4..N of|
| VP8 payload |
: :
+-+-+-+-+-+-+-+-+
| OPTIONAL RTP |
| padding |
: :
+-+-+-+-+-+-+-+-+
Figure 3
图3
A packetizer needs access to the P bit. The other fields are defined in [RFC6386], Section 9.1, and their meanings do not influence the packetization process. None of these fields are modified by the packetization process.
打包器需要访问P位。其他字段在[RFC6386]第9.1节中定义，其含义不影响打包过程。这些字段都不会被打包过程修改。
P: Inverse key frame flag. When set to 0, the current frame is a key frame. When set to 1, the current frame is an interframe. Defined in [RFC6386]
P：反向关键帧标志。设置为0时，当前帧是关键帧。设置为1时，当前帧为帧间帧。在[RFC6386]中定义
An encoded VP8 frame can be divided into two or more partitions, as described in Section 1. It is OPTIONAL for a packetizer implementing this RTP specification to pay attention to the partition boundaries within an encoded frame. If packetization of a frame is done without considering the partition boundaries, the PID field MAY be set to 0 for all packets and the S bit MUST NOT be set to 1 for any other packet than the first.
编码的VP8帧可以划分为两个或多个分区，如第1节所述。对于实现此RTP规范的打包器来说，关注编码帧内的分区边界是可选的。如果在不考虑分区边界的情况下完成帧的分组，则对于所有分组，PID字段可以设置为0，对于第一个分组以外的任何其他分组，S位不得设置为1。
If the preferred usage suggested in Section 3 is followed, with each packet carrying data from exactly one partition, the S bit and PID fields described in Section 4.2 SHOULD be used to indicate what the packet contains. The PID field should indicate to which partition the first octet of the payload belongs and the S bit indicates that the packet starts on a new partition.
如果遵循第3节中建议的首选用法，且每个数据包仅承载一个分区的数据，则应使用第4.2节中描述的S位和PID字段来指示数据包包含的内容。PID字段应指示有效负载的第一个八位字节属于哪个分区，S位指示数据包从新分区开始。
If the packetizer does not pay attention to the partition boundaries, one packet can contain a fragment of a partition, a complete partition, or an aggregate of fragments and partitions. There is no explicit signaling of partition boundaries in the payload, and the partition lengths at the end of the first partition have to be used to identify the boundaries. Partitions MUST be aggregated in decoding order. Two fragments from different partitions MAY be aggregated into the same packet along with one or more complete partitions.
如果packetizer不注意分区边界，那么一个数据包可以包含一个分区的片段、一个完整的分区或一个片段和分区的集合。有效负载中没有分区边界的显式信令，必须使用第一个分区末尾的分区长度来标识边界。分区必须按解码顺序聚合。来自不同分区的两个片段可以与一个或多个完整分区一起聚合到同一个数据包中。
In all cases, the payload of a packet MUST contain data from only one video frame. Consequently, the set of packets carrying the data from a particular frame will contain exactly one VP8 Payload Header (see Section 4.3) carried in the first packet of the frame. The last, or only, packet carrying data for the frame MUST have the M bit set in the RTP header.
在所有情况下，数据包的有效载荷必须仅包含来自一个视频帧的数据。因此，承载来自特定帧的数据的数据包集将恰好包含在该帧的第一个数据包中承载的一个VP8有效负载报头（参见第4.3节）。最后一个（或仅一个）承载帧数据的数据包必须在RTP报头中设置M位。
Example of frame reconstruction algorithm.
帧重建算法实例。
1: Collect all packets with a given RTP timestamp.
1：收集具有给定RTP时间戳的所有数据包。
2: Go through packets in order, sorted by sequence numbers, if packets are missing, send NACK as defined in [RFC4585] or decode with missing partitions, see Section 4.5.2 below.
2：按顺序检查数据包，按序列号排序，如果数据包丢失，则发送[RFC4585]中定义的NACK，或使用丢失的分区进行解码，见下文第4.5.2节。
3: A frame is complete if the frame has no missing sequence numbers, the first packet in the frame contains S=1 with partId=0 and the last packet in the frame has the marker bit set.
3：如果帧没有丢失的序列号，则帧中的第一个数据包包含S=1且partId=0，并且帧中的最后一个数据包设置了标记位，则帧完成。
Example of partition reconstruction algorithm. The algorithm only applies for the RECOMMENDED use case with partitions in separate packets.
分区重建算法实例。该算法仅适用于推荐的使用案例，其中分区位于单独的数据包中。
1: Scan for the start of a new partition; S=1.
1：扫描新分区的开始；S=1。
2: Continue scan to detect end of partition; hence, a new S=1 (previous packet was the end of the partition) is found or the marker bit is set. If a loss is detected before the end of the partition, abandon all packets in this partition and continue the scan repeating from step 1.
2：继续扫描以检测分区结束；因此，找到一个新的S=1（以前的数据包是分区的结尾）或设置标记位。如果在分区结束之前检测到丢失，请放弃该分区中的所有数据包，并继续从步骤1开始重复扫描。
3: Store the packets in the complete partition, continue the scan repeating from step 1 until end of frame is reached.
3：将数据包存储在完整分区中，继续从步骤1重复扫描，直到到达帧结束。
4: Send all complete partitions to the decoder. If no complete partition is found discard the whole frame.
4：将所有完整的分区发送到解码器。如果没有找到完整的分区，则丢弃整个帧。
A few examples of how the VP8 RTP payload can be used are included below.
以下是一些如何使用VP8 RTP有效负载的示例。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
|Size0|1| VER |0| P = 0
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| VP8 payload |
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
|Size0|1| VER |0| P = 0
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| VP8 payload |
+-+-+-+-+-+-+-+-+
4.6.2. Non-discardable VP8 Interframe in a Single RTP Packet; No PictureID
4.6.2. 单个RTP包中的不可丢弃VP8帧间；无图片索引
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|0|0|0|1|0|0 0 0| X = 0; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1| P = 1
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| VP8 payload |
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|0|0|0|1|0|0 0 0| X = 0; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1| P = 1
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| VP8 payload |
+-+-+-+-+-+-+-+-+
First RTP packet; complete first partition.
第一RTP包；完成第一个分区。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1| P = 1
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Octets 4..L of|
| first VP8 |
| partition |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1| P = 1
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Octets 4..L of|
| first VP8 |
| partition |
: :
+-+-+-+-+-+-+-+-+
Second RTP packet; complete second partition.
第二RTP包；完成第二个分区。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 1| X = 1; S = 1; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| Remaining VP8 |
| partitions |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 1| X = 1; S = 1; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| Remaining VP8 |
| partitions |
: :
+-+-+-+-+-+-+-+-+
First RTP packet; complete first partition.
第一RTP包；完成第一个分区。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1| P = 1
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Complete |
| first |
| partition |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1| P = 1
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Complete |
| first |
| partition |
: :
+-+-+-+-+-+-+-+-+
Second RTP packet; first fragment of second partition.
第二RTP包；第二个分区的第一个片段。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 1| X = 1; S = 1; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| First fragment|
| of second |
| partition |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 1| X = 1; S = 1; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| First fragment|
| of second |
| partition |
: :
+-+-+-+-+-+-+-+-+
Third RTP packet; second fragment of second partition.
第三个RTP包；第二个分区的第二个片段。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|0|0|0 0 1| X = 1; S = 0; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| Mid fragment |
| of second |
| partition |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 0 |
+-+-+-+-+-+-+-+-+
|1|0|0|0|0|0 0 1| X = 1; S = 0; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| Mid fragment |
| of second |
| partition |
: :
+-+-+-+-+-+-+-+-+
Fourth RTP packet; last fragment of second partition.
第四个RTP包；第二个分区的最后一个片段。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|0|0|0 0 1| X = 1; S = 0; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| Last fragment |
| of second |
| partition |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|0|0|0 0 1| X = 1; S = 0; PID = 1
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1
+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 1| PictureID = 17
+-+-+-+-+-+-+-+-+
| Last fragment |
| of second |
| partition |
: :
+-+-+-+-+-+-+-+-+
PictureID = 4711 = 001001001100111 binary (first 7 bits: 0010010, last 8 bits: 01100111).
PictureID=4711=001100111二进制（前7位：0010010，后8位：01100111）。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1;
+-+-+-+-+-+-+-+-+
|1 0 0 1 0 0 1 0| Long PictureID flag = 1
|0 1 1 0 0 1 1 1| PictureID = 4711
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1|
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Octets 4..N of|
| VP8 payload |
: :
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| RTP header |
| M = 1 |
+-+-+-+-+-+-+-+-+
|1|0|0|1|0|0 0 0| X = 1; S = 1; PID = 0
+-+-+-+-+-+-+-+-+
|1|0|0|0|0 0 0 0| I = 1;
+-+-+-+-+-+-+-+-+
|1 0 0 1 0 0 1 0| Long PictureID flag = 1
|0 1 1 0 0 1 1 1| PictureID = 4711
+-+-+-+-+-+-+-+-+
|Size0|1| VER |1|
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Octets 4..N of|
| VP8 payload |
: :
+-+-+-+-+-+-+-+-+
The VP8 payload descriptor defined in Section 4.2 contains an optional PictureID parameter. This parameter is included mainly to enable use of reference picture selection indication (RPSI) and slice loss indication (SLI), both defined in [RFC4585].
第4.2节中定义的VP8有效负载描述符包含可选的PictureID参数。该参数主要用于启用参考图片选择指示（RPSI）和切片丢失指示（SLI），两者均在[RFC4585]中定义。
The RPSI 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 VP8 used for point-to-point (unicast) communication. The use of RPSI for VP8 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
RPSI是在基于RTCP的反馈格式中定义的特定于有效负载的反馈消息。RPSI消息由接收器生成，可通过两种方式使用。或者，当解码器检测到丢失时，它可以向优选参考图片发送信号——最好是解码器知道的参考图片是完美的——或者它可以用作肯定某些参考图片的正确解码的正反馈信息。正反馈方法适用于用于点对点（单播）通信的VP8。VP8的RPSI的使用最好与编解码器的两个特殊参考帧的特殊更新模式相结合——黄金帧和altref帧——其中
they are updated in an alternating leapfrog fashion. When a receiver has received and correctly decoded a golden or altref frame, and that frame has a PictureID in the payload descriptor, the receiver can acknowledge this simply by sending an RPSI message back to the sender. The message body (i.e., the "native RPSI bit string" in [RFC4585]) is simply the PictureID of the received frame.
它们以交替跳跃式方式更新。当接收器已接收并正确解码golden或altref帧，且该帧在有效负载描述符中具有PictureID时，接收器可通过将RPSI消息发送回发送者来确认这一点。消息体（即，[RFC4585]中的“本机RPSI位字符串”）只是接收帧的PictureID。
The SLI 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]:
SLI是在基于RTCP的反馈格式中定义的另一个特定于有效负载的反馈消息。当在帧中检测到丢失或损坏时，接收器生成SLI消息。SLI消息的格式如下[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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 4
图4
Here, First is the macroblock address (in scan order) of the first lost block and Number is the number of lost blocks, as defined in [RFC4585]. PictureID is the six least significant bits of the codec-specific picture identifier in which the loss or corruption has occurred. For VP8, 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 part 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.
这里，First是第一个丢失块的宏块地址（按扫描顺序），Number是丢失块的数量，如[RFC4585]中所定义。PictureID是发生丢失或损坏的编解码器特定图片标识符的六个最低有效位。对于VP8，这个特定于编解码器的标识符自然是当前帧的PictureID，从有效负载描述符读取。如果当前帧的有效负载描述符没有PictureID，则接收器可以在SLI消息中发送最后接收到的PictureID+1。接收机可以将第一个参数设置为0，将Number参数设置为每帧宏块的总数，即使只有部分帧被损坏。当发送方收到SLI消息时，它可以利用最近收到的RPSI消息中的知识。知道最后一个golden或altref帧已成功接收，它可以参考该已建立的参考对下一帧进行编码。
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 sent instead. Once the new golden frame is established and acknowledged, the same rule applies when updating the altref frame.
RPSI和SLI的使用在示例中得到了最好的说明。在此示例中，编码器可能不会更新altref帧，直到最后发送的黄金帧已被RPSI消息确认。如果在一段时间内未收到更新，则会发送新的金框更新。一旦建立并确认了新的黄金框架，更新altref框架时同样的规则也适用。
+-------+-------------------+-------------------------+-------------+
| 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) | |
| | | | |
| 1202 | Receive RPSI(200) | | altref |
| | | | |
+-------+-------------------+-------------------------+-------------+
| 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) | |
| | | | |
| 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 |
+-------+-------------------+-------------------------+-------------+
| ... | (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
表1：发送方和接收方之间的信令示例
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.
注意，该方案对反馈消息的丢失具有鲁棒性。如果RPSI丢失，发送方将在一段时间后再次尝试更新golden（或altref），而不释放已建立的引用。此外，如果SLI丢失，只要图片损坏，接收器可以按照[RFC4585]中规定的RTCP发送定时限制允许的任何间隔继续发送SLI消息。
This payload format has two optional parameters.
此有效负载格式有两个可选参数。
This registration is done using the template defined in [RFC6838] and following [RFC4855].
此注册使用[RFC6838]中定义的模板和以下[RFC4855]完成。
Type name: video
类型名称：视频
Subtype name: VP8
子类型名称：VP8
Required parameters: None.
所需参数：无。
Optional parameters:
可选参数：
These parameters are used to signal the capabilities of a receiver implementation. If the implementation is willing to receive media, both parameters MUST be provided. These parameters MUST NOT be used for any other purpose.
这些参数用于表示接收器实现的能力。如果实现愿意接收介质，则必须提供这两个参数。这些参数不得用于任何其他目的。
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-fr：max-fr的值是一个整数，表示解码器能够解码的最大帧速率（以每秒帧数为单位）。
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.
max fs：max fs的值是一个整数，表示解码器能够解码的最大帧大小（以宏块为单位）。
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).
只要宏块中帧的宽度和高度小于int（sqrt（max fs*8）），解码器就能够解码该帧大小。例如，最大fs为1200（能够支持640x480分辨率）将支持高达1552像素（97个宏块）的宽度和高度。
Encoding considerations: This media type is framed in RTP and contains binary data; see Section 4.8 of [RFC6838].
编码注意事项：此媒体类型在RTP中设置帧并包含二进制数据；见[RFC6838]第4.8节。
Security considerations: See Section 7 of RFC 7741.
安全注意事项：见RFC 7741第7节。
Interoperability considerations: None.
互操作性考虑：无。
Published specification: VP8 bitstream format [RFC6386] and RFC 7741.
已发布规范：VP8位流格式[RFC6386]和RFC 7741。
Applications that use this media type: For example: Video over IP, video conferencing.
使用此媒体类型的应用程序：例如：IP视频、视频会议。
Fragment identifier considerations: N/A.
片段标识符注意事项：不适用。
Additional information: None.
其他信息：无。
Person & email address to contact for further information: Patrik Westin, patrik.westin@gmail.com
联系人和电子邮件地址，以获取更多信息：Patrik Westin，Patrik。westin@gmail.com
Intended usage: COMMON
预期用途：普通
Restrictions on usage: This media type depends on RTP framing, and hence it is only defined for transfer via RTP [RFC3550].
使用限制：此媒体类型取决于RTP帧，因此仅定义为通过RTP传输[RFC3550]。
Author: Patrik Westin, patrik.westin@gmail.com
作者：帕特里克·威斯汀，帕特里克。westin@gmail.com
Change controller: IETF Payload Working Group delegated from the IESG.
变更控制员：IESG授权的IETF有效载荷工作组。
The receiver MUST ignore any fmtp parameter unspecified in this memo.
接收方必须忽略本备忘录中未指定的任何fmtp参数。
The media type video/VP8 string is mapped to fields in the Session Description Protocol (SDP) [RFC4566] as follows:
媒体类型视频/VP8字符串映射到会话描述协议（SDP）[RFC4566]中的字段，如下所示：
o The media name in the "m=" line of SDP MUST be video.
o SDP的“m=”行中的媒体名称必须是视频。
o The encoding name in the "a=rtpmap" line of SDP MUST be VP8 (the media subtype).
o SDP的“a=rtpmap”行中的编码名称必须是VP8（媒体子类型）。
o The clock rate in the "a=rtpmap" line MUST be 90000.
o “a=rtpmap”行中的时钟频率必须为90000。
o The parameters "max-fs" and "max-fr" MUST be included in the "a=fmtp" line if the SDP is used to declare receiver capabilities. These parameters are expressed as a media subtype string, in the form of a semicolon-separated list of parameter=value pairs.
o 如果SDP用于声明接收机能力，则参数“max fs”和“max fr”必须包含在“a=fmtp”行中。这些参数表示为媒体子类型字符串，以分号分隔的参数=值对列表的形式。
An example of media representation in SDP is as follows:
SDP中的媒体表示示例如下：
m=video 49170 RTP/AVPF 98
a=rtpmap:98 VP8/90000
a=fmtp:98 max-fr=30; max-fs=3600;
m=video 49170 RTP/AVPF 98
a=rtpmap:98 VP8/90000
a=fmtp:98 max-fr=30; max-fs=3600;
The VP8 codec offers a decode complexity that is roughly linear with the number of pixels encoded. The parameters "max-fr" and "max-fs" are defined in Section 6.1, where the macroblock size is 16x16 pixels as defined in [RFC6386], the max-fs and max-fr parameters MUST be used to establish these limits.
VP8编解码器提供的解码复杂度与编码像素数大致呈线性关系。参数“max fr”和“max fs”在第6.1节中定义，其中宏块大小为[RFC6386]中定义的16x16像素，必须使用max fs和max fr参数来确定这些限制。
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 such as RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711], or RTP/ SAVPF [RFC5124]. However, as "Securing the RTP Protocol Framework: Why RTP Does Not Mandate a Single Media Security Solution" [RFC7202] discusses, it is not an RTP payload format's responsibility to discuss or mandate what solutions are used to meet the basic security goals like confidentiality, integrity, and source authenticity for RTP in general. This responsibility lays on anyone using RTP in an application. They can find guidance on available security mechanisms and important considerations in "Options for Securing RTP Sessions" [RFC7201]. Applications SHOULD use one or more appropriate strong security mechanisms. The rest of this security consideration section discusses the security impacting properties of the payload format itself.
使用本规范中定义的有效负载格式的RTP数据包受RTP规范[RFC3550]和任何适用RTP配置文件（如RTP/AVP[RFC3551]、RTP/AVPF[RFC4585]、RTP/SAVP[RFC3711]或RTP/SAVPF[RFC5124]中讨论的安全注意事项的约束。然而，正如[RFC7202]所讨论的“保护RTP协议框架：为什么RTP不强制要求单一媒体安全解决方案”，RTP有效负载格式不负责讨论或强制要求使用什么解决方案来满足RTP的基本安全目标，如机密性、完整性和源真实性。这一责任由在应用程序中使用RTP的任何人承担。他们可以在“保护RTP会话的选项”[RFC7201]中找到关于可用安全机制和重要注意事项的指导。应用程序应使用一个或多个适当的强安全机制。本安全考虑部分的其余部分将讨论影响有效负载格式本身安全性的属性。
This RTP payload format and its media decoder do not exhibit any significant difference 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.
这种RTP有效载荷格式及其媒体解码器在数据包处理的接收方计算复杂度方面没有表现出任何显著差异，因此，不太可能由于接收病理数据而造成拒绝服务威胁。RTP有效负载格式也不包含任何活动内容。
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 VP8 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).
RTP的拥塞控制应根据RFC 3550[RFC3550]和任何适用的RTP配置文件使用；e、 g.，RFC 3551[RFC3551]。在实时编码场景中，拥塞控制机制可以通过指示编码器以特定目标速率编码来调整传输速率。媒体感知网络元件可使用第4.2节中VP8有效负载描述符中的信息来识别非参考帧并丢弃它们，以减少网络拥塞。请注意，如果流是加密的（因为非引用标记是加密的），则不能丢弃非引用帧。
The IANA has registered a media type as described in Section 6.1.
IANA已注册第6.1节所述的媒体类型。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，DOI 10.17487/RFC2119，1997年3月<http://www.rfc-editor.org/info/rfc2119>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, July 2003, <http://www.rfc-editor.org/info/rfc3550>.
[RFC3550]Schulzrinne，H.，Casner，S.，Frederick，R.，和V.Jacobson，“RTP：实时应用的传输协议”，STD 64，RFC 3550，DOI 10.17487/RFC3550，2003年7月<http://www.rfc-editor.org/info/rfc3550>.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, DOI 10.17487/RFC3551, July 2003, <http://www.rfc-editor.org/info/rfc3551>.
[RFC3551]Schulzrinne，H.和S.Casner，“具有最小控制的音频和视频会议的RTP配置文件”，STD 65，RFC 3551，DOI 10.17487/RFC3551，2003年7月<http://www.rfc-editor.org/info/rfc3551>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, DOI 10.17487/RFC4566, July 2006, <http://www.rfc-editor.org/info/rfc4566>.
[RFC4566]Handley，M.，Jacobson，V.，和C.Perkins，“SDP：会话描述协议”，RFC 4566，DOI 10.17487/RFC4566，2006年7月<http://www.rfc-editor.org/info/rfc4566>.
[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, DOI 10.17487/RFC4585, July 2006, <http://www.rfc-editor.org/info/rfc4585>.
[RFC4585]Ott，J.，Wenger，S.，Sato，N.，Burmeister，C.，和J.Rey，“基于实时传输控制协议（RTCP）的反馈（RTP/AVPF）的扩展RTP配置文件”，RFC 4585，DOI 10.17487/RFC4585，2006年7月<http://www.rfc-editor.org/info/rfc4585>.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, <http://www.rfc-editor.org/info/rfc4855>.
[RFC4855]Casner，S.，“RTP有效载荷格式的媒体类型注册”，RFC 4855，DOI 10.17487/RFC4855，2007年2月<http://www.rfc-editor.org/info/rfc4855>.
[RFC6386] Bankoski, J., Koleszar, J., Quillio, L., Salonen, J., Wilkins, P., and Y. Xu, "VP8 Data Format and Decoding Guide", RFC 6386, DOI 10.17487/RFC6386, November 2011, <http://www.rfc-editor.org/info/rfc6386>.
[RFC6386]Bankoski，J.，Koleszar，J.，Quillio，L.，Salonen，J.，Wilkins，P.，和Y.Xu，“VP8数据格式和解码指南”，RFC 6386，DOI 10.17487/RFC6386，2011年11月<http://www.rfc-editor.org/info/rfc6386>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, <http://www.rfc-editor.org/info/rfc6838>.
[RFC6838]Freed，N.，Klensin，J.和T.Hansen，“介质类型规范和注册程序”，BCP 13，RFC 6838，DOI 10.17487/RFC6838，2013年1月<http://www.rfc-editor.org/info/rfc6838>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, DOI 10.17487/RFC3711, March 2004, <http://www.rfc-editor.org/info/rfc3711>.
[RFC3711]Baugher，M.，McGrew，D.，Naslund，M.，Carrara，E.，和K.Norrman，“安全实时传输协议（SRTP）”，RFC 3711，DOI 10.17487/RFC3711，2004年3月<http://www.rfc-editor.org/info/rfc3711>.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 2008, <http://www.rfc-editor.org/info/rfc5124>.
[RFC5124]Ott，J.和E.Carrara，“基于实时传输控制协议（RTCP）的反馈扩展安全RTP配置文件（RTP/SAVPF）”，RFC 5124DOI 10.17487/RFC5124，2008年2月<http://www.rfc-editor.org/info/rfc5124>.
[RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, <http://www.rfc-editor.org/info/rfc7201>.
[RFC7201]Westerlund，M.和C.Perkins，“保护RTP会话的选项”，RFC 7201，DOI 10.17487/RFC7201，2014年4月<http://www.rfc-editor.org/info/rfc7201>.
[RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP Framework: Why RTP Does Not Mandate a Single Media Security Solution", RFC 7202, DOI 10.17487/RFC7202, April 2014, <http://www.rfc-editor.org/info/rfc7202>.
[RFC7202]Perkins，C.和M.Westerlund，“保护RTP框架：为什么RTP不要求单一媒体安全解决方案”，RFC 7202，DOI 10.17487/RFC7202，2014年4月<http://www.rfc-editor.org/info/rfc7202>.
[Sch07] Schwarz, H., Marpe, D., and T. Wiegand, "Overview of the Scalable Video Coding Extension of the H.264/AVC Standard", IEEE Transactions on Circuits and Systems for Video Technology, Volume 17: Issue 9, DOI 10.1109/TCSVT.2007.905532, September 2007, <http://dx.doi.org/10.1109/TCSVT.2007.905532>.
[Schw07]Schwarz，H.，Marpe，D.，和T.Wiegand，“H.264/AVC标准的可伸缩视频编码扩展概述”，IEEE视频技术电路和系统交易，第17卷：第9期，DOI 10.1109/TCSVT.2007.905532，2007年9月<http://dx.doi.org/10.1109/TCSVT.2007.905532>.
Authors' Addresses
作者地址
Patrik Westin Google, Inc. 1600 Amphitheatre Parkway Mountain View, CA 94043 United States
帕特里克·威斯汀谷歌公司，1600圆形剧场公园路山景，美国加利福尼亚州94043
Email: patrik.westin@gmail.com
Email: patrik.westin@gmail.com
Henrik F Lundin Google, Inc. Kungsbron 2 Stockholm 11122 Sweden
亨里克·F·伦丁谷歌公司昆斯勃朗2号斯德哥尔摩11122瑞典
Email: hlundin@google.com
Email: hlundin@google.com
Michael Glover Twitter Boston 10 Hemlock Way Durham, NH 03824 United States
美国新罕布什尔州达勒姆市铁杉路10号迈克尔·格洛弗推特波士顿03824
Email: michaelglover262@gmail.com
Email: michaelglover262@gmail.com
Justin Uberti Google, Inc. 747 6th Street South Kirkland, WA 98033 United States
Justin Uberti Google，Inc.美国华盛顿州南柯克兰第六街747号，邮编：98033
Email: justin@uberti.name
Email: justin@uberti.name
Frank Galligan Google, Inc. 1600 Amphitheatre Parkway Mountain View, CA 94043 United States
Frank Galligan Google，Inc.美国加利福尼亚州山景大道1600号圆形剧场，邮编94043
Email: fgalligan@google.com
Email: fgalligan@google.com