Network Working Group
Request for Comments: 2429 C. Bormann
Category: Standards Track Univ. Bremen
L. Cline
G. Deisher
T. Gardos
C. Maciocco
D. Newell
Intel
J. Ott
Univ. Bremen
G. Sullivan
PictureTel
S. Wenger
TU Berlin
C. Zhu
Intel
October 1998
Network Working Group
Request for Comments: 2429 C. Bormann
Category: Standards Track Univ. Bremen
L. Cline
G. Deisher
T. Gardos
C. Maciocco
D. Newell
Intel
J. Ott
Univ. Bremen
G. Sullivan
PictureTel
S. Wenger
TU Berlin
C. Zhu
Intel
October 1998
RTP Payload Format for the 1998 Version of ITU-T Rec. H.263 Video (H.263+)
1998版ITU-T Rec.H.263视频（H.263+）的RTP有效载荷格式
Status of this Memo
本备忘录的状况
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (1998). All Rights Reserved.
版权所有（C）互联网协会（1998年）。版权所有。
This document specifies an RTP payload header format applicable to the transmission of video streams generated based on the 1998 version of ITU-T Recommendation H.263 [4]. Because the 1998 version of H.263 is a superset of the 1996 syntax, this format can also be used with the 1996 version of H.263 [3], and is recommended for this use by new implementations. This format does not replace RFC 2190, which continues to be used by existing implementations, and may be required for backward compatibility in new implementations. Implementations using the new features of the 1998 version of H.263 shall use the format described in this document.
本文件规定了一种RTP有效载荷报头格式，该格式适用于根据1998版ITU-T建议H.263[4]生成的视频流的传输。由于1998年版的H.263是1996年语法的超集，因此该格式也可与1996年版的H.263[3]一起使用，并建议新的实现使用该格式。此格式不会取代RFC 2190，现有实现仍在使用RFC 2190，并且在新实现中可能需要该格式以实现向后兼容性。使用1998版H.263新功能的实施应使用本文件中描述的格式。
The 1998 version of ITU-T Recommendation H.263 added numerous coding options to improve codec performance over the 1996 version. The 1998 version is referred to as H.263+ in this document. Among the new options, the ones with the biggest impact on the RTP payload specification and the error resilience of the video content are the slice structured mode, the independent segment decoding mode, the reference picture selection mode, and the scalability mode. This section summarizes the impact of these new coding options on packetization. Refer to [4] for more information on coding options.
1998年版本的ITU-T建议H.263增加了许多编码选项，以改善1996年版本的编解码器性能。1998版在本文件中称为H.263+。在这些新选项中，对RTP有效负载规范和视频内容的错误恢复能力影响最大的是切片结构模式、独立段解码模式、参考图片选择模式和可伸缩性模式。本节总结了这些新编码选项对打包的影响。有关编码选项的更多信息，请参阅[4]。
The slice structured mode was added to H.263+ for three purposes: to provide enhanced error resilience capability, to make the bitstream more amenable to use with an underlying packet transport such as RTP, and to minimize video delay. The slice structured mode supports fragmentation at macroblock boundaries.
将切片结构模式添加到H.263+中有三个目的：提供增强的错误恢复能力，使比特流更易于与底层数据包传输（如RTP）一起使用，以及最小化视频延迟。切片结构化模式支持宏块边界处的分段。
With the independent segment decoding (ISD) option, a video picture frame is broken into segments and encoded in such a way that each segment is independently decodable. Utilizing ISD in a lossy network environment helps to prevent the propagation of errors from one segment of the picture to others.
使用独立段解码（ISD）选项，视频图片帧被分成段，并以每个段都可独立解码的方式进行编码。在有损网络环境中使用ISD有助于防止错误从图片的一段传播到另一段。
The reference picture selection mode allows the use of an older reference picture rather than the one immediately preceding the current picture. Usually, the last transmitted frame is implicitly used as the reference picture for inter-frame prediction. If the reference picture selection mode is used, the data stream carries information on what reference frame should be used, indicated by the temporal reference as an ID for that reference frame. The reference picture selection mode can be used with or without a back channel, which provides information to the encoder about the internal status of the decoder. However, no special provision is made herein for carrying back channel information.
参考图片选择模式允许使用较旧的参考图片，而不是当前图片前面的参考图片。通常，最后发送的帧隐式地用作帧间预测的参考图片。如果使用参考图片选择模式，则数据流携带关于应该使用哪个参考帧的信息，该信息由时间参考指示为该参考帧的ID。参考图片选择模式可以使用或不使用反向通道，反向通道向编码器提供关于解码器内部状态的信息。然而，本文没有针对回传信道信息作出特殊规定。
H.263+ also includes bitstream scalability as an optional coding mode. Three kinds of scalability are defined: temporal, signal-to-noise ratio (SNR), and spatial scalability. Temporal scalability is achieved via the disposable nature of bi-directionally predicted frames, or B-frames. (A low-delay form of temporal scalability known as P-picture temporal scalability can also be achieved by using the reference picture selection mode described in the previous paragraph.) SNR scalability permits refinement of encoded video frames, thereby improving the quality (or SNR). Spatial scalability is similar to SNR scalability except the refinement layer is twice the size of the base layer in the horizontal dimension, vertical dimension, or both.
H.263+还包括作为可选编码模式的比特流可伸缩性。定义了三种可伸缩性：时间、信噪比（SNR）和空间可伸缩性。时间可伸缩性是通过双向预测帧或B帧的一次性性质实现的。（称为P-图片时间可伸缩性的低延迟形式的时间可伸缩性也可以通过使用前面段落中描述的参考图片选择模式来实现。）SNR可伸缩性允许对编码视频帧进行细化，从而提高质量（或SNR）。空间可伸缩性与SNR可伸缩性相似，不同之处在于细化层在水平维度、垂直维度或两者中的大小是基础层的两倍。
When transmitting H.263+ video streams over the Internet, the output of the encoder can be packetized directly. All the bits resulting from the bitstream including the fixed length codes and variable length codes will be included in the packet, with the only exception being that when the payload of a packet begins with a Picture, GOB, Slice, EOS, or EOSBS start code, the first two (all-zero) bytes of the start code are removed and replaced by setting an indicator bit in the payload header.
当通过互联网传输H.263+视频流时，编码器的输出可以直接打包。由比特流产生的包括固定长度代码和可变长度代码的所有比特将被包括在分组中，唯一的例外是当分组的有效载荷以图片、GOB、切片、EOS或EOSBS开始代码开始时，前两个（全部为零）通过在有效负载报头中设置一个指示符位，删除并替换起始代码的字节。
For H.263+ bitstreams coded with temporal, spatial, or SNR scalability, each layer may be transported to a different network address. More specifically, each layer may use a unique IP address and port number combination. The temporal relations between layers shall be expressed using the RTP timestamp so that they can be synchronized at the receiving ends in multicast or unicast applications.
对于以时间、空间或SNR可伸缩性编码的H.263+比特流，每一层可被传输到不同的网络地址。更具体地说，每一层可以使用唯一的IP地址和端口号组合。层之间的时间关系应使用RTP时间戳表示，以便在多播或单播应用中，它们可以在接收端同步。
The H.263+ video stream will be carried as payload data within RTP packets. A new H.263+ payload header is defined in section 4. This section defines the usage of the RTP fixed header and H.263+ video packet structure.
H.263+视频流将作为RTP数据包中的有效负载数据携带。第4节定义了一个新的H.263+有效载荷头。本节定义RTP固定报头和H.263+视频数据包结构的用法。
Each RTP packet starts with a fixed RTP header. The following fields of the RTP fixed header are used for H.263+ video streams:
每个RTP数据包都以一个固定的RTP报头开始。RTP固定报头的以下字段用于H.263+视频流：
Marker bit (M bit): The Marker bit of the RTP header is set to 1 when the current packet carries the end of current frame, and is 0 otherwise.
标记位（M位）：当当前数据包携带当前帧的结尾时，RTP报头的标记位设置为1，否则为0。
Payload Type (PT): The Payload Type shall specify the H.263+ video payload format.
有效载荷类型（PT）：有效载荷类型应指定H.263+视频有效载荷格式。
Timestamp: The RTP Timestamp encodes the sampling instance of the first video frame data contained in the RTP data packet. The RTP timestamp shall be the same on successive packets if a video frame occupies more than one packet. In a multilayer scenario, all pictures corresponding to the same temporal reference should use the same timestamp. If temporal scalability is used (if B-frames are present), the timestamp may not be monotonically increasing in the RTP stream. If B-frames are transmitted on a separate layer and address, they must be synchronized properly with the reference frames. Refer to the 1998 ITU-T Recommendation H.263 [4] for information on required transmission order to a decoder. For an H.263+ video stream, the RTP timestamp is based on a 90 kHz clock,
时间戳：RTP时间戳对RTP数据包中包含的第一个视频帧数据的采样实例进行编码。如果视频帧占用多个数据包，则连续数据包上的RTP时间戳应相同。在多层场景中，对应于相同时间参考的所有图片应使用相同的时间戳。如果使用时间可伸缩性（如果存在B帧），则时间戳在RTP流中可能不会单调增加。如果B帧在单独的层和地址上传输，它们必须与参考帧正确同步。参考1998年ITU-T建议H.263[4]，了解解码器所需传输顺序的信息。对于H.263+视频流，RTP时间戳基于90 kHz时钟，
the same as that of the RTP payload for H.261 stream [5]. Since both the H.263+ data and the RTP header contain time information, it is required that those timing information run synchronously. That is, both the RTP timestamp and the temporal reference (TR in the picture header of H.263) should carry the same relative timing information. Any H.263+ picture clock frequency can be expressed as 1800000/(cd*cf) source pictures per second, in which cd is an integer from 1 to 127 and cf is either 1000 or 1001. Using the 90 kHz clock of the RTP timestamp, the time increment between each coded H.263+ picture should therefore be a integer multiple of (cd*cf)/20. This will always be an integer for any "reasonable" picture clock frequency (for example, it is 3003 for 29.97 Hz NTSC, 3600 for 25 Hz PAL, 3750 for 24 Hz film, and 1500, 1250 and 1200 for the computer display update rates of 60, 72 and 75 Hz, respectively). For RTP packetization of hypothetical H.263+ bitstreams using "unreasonable" custom picture clock frequencies, mathematical rounding could become necessary for generating the RTP timestamps.
与H.261流的RTP有效载荷相同[5]。由于H.263+数据和RTP报头都包含时间信息，因此要求这些定时信息同步运行。也就是说，RTP时间戳和时间参考（H.263的图片头部中的TR）都应该携带相同的相对定时信息。任何H.263+图片时钟频率都可以表示为每秒1800000/（cd*cf）源图片，其中cd是1到127之间的整数，cf是1000或1001。因此，使用RTP时间戳的90 kHz时钟，每个编码H.263+图片之间的时间增量应为（cd*cf）/20的整数倍。对于任何“合理”的图片时钟频率，这始终是一个整数（例如，对于29.97 Hz NTSC，它是3003；对于25 Hz PAL，它是3600；对于24 Hz胶片，它是3750；对于60、72和75 Hz的计算机显示更新率，它分别是1500、1250和1200）。对于使用“不合理”自定义图片时钟频率对假设的H.263+比特流进行RTP打包，可能需要数学舍入来生成RTP时间戳。
A section of an H.263+ compressed bitstream is carried as a payload within each RTP packet. For each RTP packet, the RTP header is followed by an H.263+ payload header, which is followed by a number of bytes of a standard H.263+ compressed bitstream. The size of the H.263+ payload header is variable depending on the payload involved as detailed in the section 4. The layout of the RTP H.263+ video packet is shown as:
H.263+压缩比特流的一部分作为有效载荷在每个RTP分组中携带。对于每个RTP分组，RTP报头后面紧跟着一个H.263+有效负载报头，该报头后面紧跟着一个标准H.263+压缩比特流的若干字节。H.263+有效载荷头的大小根据第4节中详细说明的所涉及的有效载荷而变化。RTP H.263+视频包的布局如图所示：
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H.263+ Payload Header ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H.263+ Compressed Data Stream ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H.263+ Payload Header ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H.263+ Compressed Data Stream ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Any H.263+ start codes can be byte aligned by an encoder by using the stuffing mechanisms of H.263+. As specified in H.263+, picture, slice, and EOSBS starts codes shall always be byte aligned, and GOB and EOS start codes may be byte aligned. For packetization purposes, GOB start codes should be byte aligned; however, since this is not required in H.263+, there may be some cases where GOB start codes are not aligned, such as when transmitting existing content, or when using H.263 encoders that do not support GOB start code alignment. In this case, follow-on packets (see section 5.2) should be used for packetization.
通过使用H.263+的填充机制，编码器可以对任何H.263+起始代码进行字节对齐。按照H.263+中的规定，图片、切片和EOSB开始代码应始终为字节对齐，GOB和EOS开始代码可为字节对齐。出于打包目的，GOB起始代码应该是字节对齐的；然而，由于H.263+中不需要这样做，因此可能存在一些GOB开始代码未对齐的情况，例如在传输现有内容时，或者在使用不支持GOB开始代码对齐的H.263编码器时。在这种情况下，应使用后续数据包（见第5.2节）进行打包。
All H.263+ start codes (Picture, GOB, Slice, EOS, and EOSBS) begin with 16 zero-valued bits. If a start code is byte aligned and it occurs at the beginning of a packet, these two bytes shall be removed from the H.263+ compressed data stream in the packetization process and shall instead be represented by setting a bit (the P bit) in the payload header.
所有H.263+开始代码（图片、GOB、切片、EOS和EOSB）都以16个零值位开始。如果起始代码是字节对齐的，并且发生在数据包的开头，则应在数据包化过程中从H.263+压缩数据流中删除这两个字节，并通过在有效负载报头中设置位（P位）来表示。
The goals of this payload format are to specify an efficient way of encapsulating an H.263+ standard compliant bitstream and to enhance the resiliency towards packet losses. Due to the large number of different possible coding schemes in H.263+, a copy of the picture header with configuration information is inserted into the payload header when appropriate. The use of that copy of the picture header along with the payload data can allow decoding of a received packet even in such cases in which another packet containing the original picture header becomes lost.
此有效负载格式的目标是指定一种封装符合H.263+标准的比特流的有效方法，并增强对数据包丢失的恢复能力。由于H.263+中存在大量不同的可能编码方案，因此在适当的情况下，将带有配置信息的图片报头的副本插入到有效负载报头中。即使在包含原始图片报头的另一个分组丢失的情况下，使用图片报头的该副本以及有效载荷数据也可以允许对接收到的分组进行解码。
There are a few assumptions and constraints associated with this H.263+ payload header design. The purpose of this section is to point out various design issues and also to discuss several coding options provided by H.263+ that may impact the performance of network-based H.263+ video.
与此H.263+有效负载标头设计相关的一些假设和约束条件。本节的目的是指出各种设计问题，并讨论H.263+提供的可能影响基于网络的H.263+视频性能的几种编码选项。
o The optional slice structured mode described in Annex K of H.263+ [4] enables more flexibility for packetization. Similar to a picture segment that begins with a GOB header, the motion vector predictors in a slice are restricted to reside within its boundaries. However, slices provide much greater freedom in the selection of the size and shape of the area which is represented as a distinct decodable region. In particular, slices can have a size which is dynamically selected to allow the data for each slice to fit into a chosen packet size. Slices can also be chosen to have a rectangular shape which is conducive for minimizing the impact of errors and packet losses on motion compensated prediction. For these reasons, the use of the slice structured mode is strongly recommended for any applications used in environments where significant packet loss occurs.
o H.263+[4]附录K中描述的可选切片结构模式使打包更加灵活。与以GOB头开始的图片片段类似，切片中的运动矢量预测器被限制在其边界内。然而，切片在选择区域的大小和形状方面提供了更大的自由度，该区域被表示为一个不同的可解码区域。特别地，片可以具有动态选择的大小，以允许每个片的数据适合所选择的分组大小。切片也可以选择具有矩形形状，这有助于最小化错误和分组丢失对运动补偿预测的影响。由于这些原因，强烈建议在发生重大数据包丢失的环境中使用切片结构化模式。
o In non-rectangular slice structured mode, only complete slices should be included in a packet. In other words, slices should not be fragmented across packet boundaries. The only reasonable need for a slice to be fragmented across packet boundaries is when the encoder which generated the H.263+ data stream could not be influenced by an awareness of the packetization process (such as when sending H.263+ data through a network other than the one to which the encoder is attached, as in network gateway
o 在非矩形切片结构模式下，数据包中只应包含完整的切片。换句话说，切片不应该跨包边界分割。在生成H.263+数据流的编码器不能受到对分组化过程的感知的影响时（例如，当通过编码器所连接的网络以外的网络发送H.263+数据时，如在网络网关中），跨分组边界分割片的唯一合理需要是
implementations). Optimally, each packet will contain only one slice.
实现）。最佳情况下，每个数据包将只包含一个切片。
o The independent segment decoding (ISD) described in Annex R of [4] prevents any data dependency across slice or GOB boundaries in the reference picture. It can be utilized to further improve resiliency in high loss conditions.
o [4]附录R中所述的独立段解码（ISD）可防止参考图片中跨片或GOB边界的任何数据依赖性。它可用于进一步提高高损耗条件下的弹性。
o If ISD is used in conjunction with the slice structure, the rectangular slice submode shall be enabled and the dimensions and quantity of the slices present in a frame shall remain the same between each two intra-coded frames (I-frames), as required in H.263+. The individual ISD segments may also be entirely intra coded from time to time to realize quick error recovery without adding the latency time associated with sending complete INTRA-pictures.
o 如果ISD与切片结构一起使用，则应启用矩形切片子模式，并且帧中存在的切片的尺寸和数量应在每两个帧内编码帧（I帧）之间保持相同，如H.263+所要求。各个ISD段还可以不时地完全进行帧内编码，以实现快速错误恢复，而不增加与发送完整帧内图片相关联的延迟时间。
o When the slice structure is not applied, the insertion of a (preferably byte-aligned) GOB header can be used to provide resync boundaries in the bitstream, as the presence of a GOB header eliminates the dependency of motion vector prediction across GOB boundaries. These resync boundaries provide natural locations for packet payload boundaries.
o 当不应用切片结构时，插入（优选字节对齐的）GOB报头可用于在比特流中提供重新同步边界，因为GOB报头的存在消除了跨GOB边界的运动矢量预测的依赖性。这些重新同步边界为数据包有效负载边界提供了自然位置。
o H.263+ allows picture headers to be sent in an abbreviated form in order to prevent repetition of overhead information that does not change from picture to picture. For resiliency, sending a complete picture header for every frame is often advisable. This means that (especially in cases with high packet loss probability in which picture header contents are not expected to be highly predictable), the sender may find it advisable to always set the subfield UFEP in PLUSPTYPE to '001' in the H.263+ video bitstream. (See [4] for the definition of the UFEP and PLUSPTYPE fields).
o H.263+允许以缩写形式发送图片标题，以防止重复开销信息，而这些信息不会在图片之间改变。为了提高弹性，通常建议为每一帧发送一个完整的图片标题。这意味着（特别是在具有高分组丢失概率的情况下，其中图片报头内容不期望是高度可预测的），发送方可能发现建议在H.263+视频比特流中始终将PLUSPTYPE中的子字段UFEP设置为“001”。（有关UFEP和PLUSPTYPE字段的定义，请参见[4]）。
o In a multi-layer scenario, each layer may be transmitted to a different network address. The configuration of each layer such as the enhancement layer number (ELNUM), reference layer number (RLNUM), and scalability type should be determined at the start of the session and should not change during the course of the session.
o 在多层方案中，每一层可以被传输到不同的网络地址。每个层的配置，如增强层编号（ELNUM）、参考层编号（RLNUM）和可伸缩性类型，应在会话开始时确定，并且在会话过程中不应更改。
o All start codes can be byte aligned, and picture, slice, and EOSBS start codes are always byte aligned. The boundaries of these syntactical elements provide ideal locations for placing packet boundaries.
o 所有开始代码都可以是字节对齐的，图片、切片和EOSB开始代码始终是字节对齐的。这些语法元素的边界为放置数据包边界提供了理想的位置。
o We assume that a maximum Picture Header size of 504 bits is sufficient. The syntax of H.263+ does not explicitly prohibit larger picture header sizes, but the use of such extremely large picture headers is not expected.
o 我们假设504位的最大图片头大小就足够了。H.263+的语法没有明确禁止较大的图片标题大小，但不希望使用如此大的图片标题。
For H.263+ video streams, each RTP packet carries only one H.263+ video packet. The H.263+ payload header is always present for each H.263+ video packet. The payload header is of variable length. A 16 bit field of the basic payload header may be followed by an 8 bit field for Video Redundancy Coding (VRC) information, and/or by a variable length extra picture header as indicated by PLEN. These optional fields appear in the order given above when present.
对于H.263+视频流，每个RTP数据包仅携带一个H.263+视频数据包。对于每个H.263+视频数据包，始终存在H.263+有效负载报头。有效负载收割台长度可变。基本有效载荷报头的16位字段后面可以是用于视频冗余编码（VRC）信息的8位字段，和/或如PLEN所示的可变长度额外图片报头。这些可选字段在出现时按上述顺序显示。
If an extra picture header is included in the payload header, the length of the picture header in number of bytes is specified by PLEN. The minimum length of the payload header is 16 bits, corresponding to PLEN equal to 0 and no VRC information present.
如果有效负载标头中包含额外图片标头，则以字节为单位的图片标头长度由PLEN指定。有效负载报头的最小长度为16位，对应于等于0且不存在VRC信息的PLEN。
The remainder of this section defines the various components of the RTP payload header. Section five defines the various packet types that are used to carry different types of H.263+ coded data, and section six summarizes how to distinguish between the various packet types.
本节的其余部分定义了RTP有效负载标头的各个组件。第五节定义了用于承载不同类型的H.263+编码数据的各种数据包类型，第六节总结了如何区分各种数据包类型。
The H.263+ payload header is structured as follows:
H.263+有效负载标头的结构如下：
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |P|V| PLEN |PEBIT|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |P|V| PLEN |PEBIT|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RR: 5 bits Reserved bits. Shall be zero.
RR:5位保留位。应为零。
P: 1 bit Indicates the picture start or a picture segment (GOB/Slice) start or a video sequence end (EOS or EOSBS). Two bytes of zero bits then have to be prefixed to the payload of such a packet to compose a complete picture/GOB/slice/EOS/EOSBS start code. This bit allows the omission of the two first bytes of the start codes, thus improving the compression ratio.
P:1位表示图片开始或图片段（GOB/切片）开始或视频序列结束（EOS或EOSB）。然后，必须在这样一个数据包的有效负载前加上两个字节的零位前缀，以组成完整的picture/GOB/slice/EOS/EOSBS开始代码。该位允许省略起始码的前两个字节，从而提高压缩比。
V: 1 bit Indicates the presence of an 8 bit field containing information for Video Redundancy Coding (VRC), which follows immediately after the initial 16 bits of the payload header if present. For syntax and semantics of that 8 bit VRC field see section 4.2.
V:1位表示存在包含视频冗余编码（VRC）信息的8位字段，该字段紧跟在有效负载报头的初始16位之后（如果存在）。有关8位VRC字段的语法和语义，请参见第4.2节。
PLEN: 6 bits Length in bytes of the extra picture header. If no extra picture header is attached, PLEN is 0. If PLEN>0, the extra picture header is attached immediately following the rest of the payload header. Note the length reflects the omission of the first two bytes of the picture start code (PSC). See section 5.1.
PLEN：额外图片标题的6位字节长度。如果未附加额外图片标题，则PLEN为0。如果PLEN>0，额外图片标头将紧跟在有效负载标头的其余部分之后。注：长度反映了图片开始代码（PSC）前两个字节的省略。见第5.1节。
PEBIT: 3 bits Indicates the number of bits that shall be ignored in the last byte of the picture header. If PLEN is not zero, the ignored bits shall be the least significant bits of the byte. If PLEN is zero, then PEBIT shall also be zero.
PEBIT:3位表示图片标题最后一个字节中应忽略的位数。如果PLEN不为零，则忽略的位应为字节的最低有效位。如果PLEN为零，则PEBIT也应为零。
Video Redundancy Coding (VRC) is an optional mechanism intended to improve error resilience over packet networks. Implementing VRC in H.263+ will require the Reference Picture Selection option described in Annex N of [4]. By having multiple "threads" of independently inter-frame predicted pictures, damage of individual frame will cause distortions only within its own thread but leave the other threads unaffected. From time to time, all threads converge to a so-called sync frame (an INTRA picture or a non-INTRA picture which is redundantly represented within multiple threads); from this sync frame, the independent threads are started again. For more information on codec support for VRC see [7].
视频冗余编码（VRC）是一种可选机制，旨在提高分组网络的容错能力。在H.263+中实现VRC需要参考图片选择选项，如[4]附录N所述。通过拥有独立帧间预测图片的多个“线程”，单个帧的损坏将仅在其自身线程内引起失真，而不影响其他线程。有时，所有线程会聚到所谓的同步帧（在多个线程中冗余表示的帧内图片或非帧内图片）；在此同步帧中，独立线程将再次启动。有关VRC编解码器支持的更多信息，请参见[7]。
P-picture temporal scalability is another use of the reference picture selection mode and can be considered a special case of VRC in which only one copy of each sync frame may be sent. It offers a thread-based method of temporal scalability without the increased delay caused by the use of B pictures. In this use, sync frames sent in the first thread of pictures are also used for the prediction of a second thread of pictures which fall temporally between the sync frames to increase the resulting frame rate. In this use, the pictures in the second thread can be discarded in order to obtain a reduction of bit rate or decoding complexity without harming the ability to decode later pictures. A third or more threads can also be added as well, but each thread is predicted only from the sync frames (which are sent at least in thread 0) or from frames within the same thread.
P-图片时间可伸缩性是参考图片选择模式的另一个用途，并且可以被视为VRC的特殊情况，其中每个同步帧的一个副本可以被发送。它提供了一种基于线程的时间可伸缩性方法，而不会因使用B图片而增加延迟。在该使用中，在第一图片线程中发送的同步帧还用于预测在同步帧之间暂时落下的第二图片线程，以增加结果帧速率。在这种使用中，可以丢弃第二线程中的图片，以便在不损害解码后续图片的能力的情况下获得比特率或解码复杂度的降低。也可以添加第三个或更多线程，但每个线程仅从同步帧（至少在线程0中发送）或同一线程内的帧进行预测。
While a VRC data stream is - like all H.263+ data - totally self-contained, it may be useful for the transport hierarchy implementation to have knowledge about the current damage status of each thread. On the Internet, this status can easily be determined by observing the marker bit, the sequence number of the RTP header, and the thread-id and a circling "packet per thread" number. The latter two numbers are coded in the VRC header extension.
虽然与所有H.263+数据一样，VRC数据流是完全独立的，但对于传输层次结构实现来说，了解每个线程的当前损坏状态可能是有用的。在Internet上，通过观察标记位、RTP头的序列号、线程id和循环的“每个线程的数据包”号，可以很容易地确定这种状态。后两个数字在VRC标题扩展中编码。
The format of the VRC header extension is as follows:
VRC标头扩展的格式如下所示：
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| TID | Trun |S|
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| TID | Trun |S|
+-+-+-+-+-+-+-+-+
TID: 3 bits Thread ID. Up to 7 threads are allowed. Each frame of H.263+ VRC data will use as reference information only sync frames or frames within the same thread. By convention, thread 0 is expected to be the "canonical" thread, which is the thread from which the sync frame should ideally be used. In the case of corruption or loss of the thread 0 representation, a representation of the sync frame with a higher thread number can be used by the decoder. Lower thread numbers are expected to contain equal or better representations of the sync frames than higher thread numbers in the absence of data corruption or loss. See [7] for a detailed discussion of VRC.
TID:3位线程ID。最多允许7个线程。H.263+VRC数据的每个帧将仅使用同步帧或同一线程内的帧作为参考信息。按照约定，线程0应该是“规范”线程，这是理想情况下使用同步帧的线程。在线程0表示损坏或丢失的情况下，解码器可以使用具有更高线程号的同步帧表示。在没有数据损坏或丢失的情况下，较低的线程号应包含与较高的线程号相同或更好的同步帧表示。有关VRC的详细讨论，请参见[7]。
Trun: 4 bits Monotonically increasing (modulo 16) 4 bit number counting the packet number within each thread.
Trun：4位单调递增（模16）4位数，计算每个线程内的包数。
S: 1 bit A bit that indicates that the packet content is for a sync frame. An encoder using VRC may send several representations of the same "sync" picture, in order to ensure that regardless of which thread of pictures is corrupted by errors or packet losses, the reception of at least one representation of a particular picture is ensured (within at least one thread). The sync picture can then be used for the prediction of any thread. If packet losses have not occurred, then the sync frame contents of thread 0 can be used and those of other threads can be discarded (and similarly for other threads). Thread 0 is considered the "canonical" thread, the use of which is preferable to all others. The contents of packets having lower thread numbers shall be considered as having a higher processing and delivery priority than those with higher thread numbers. Thus packets having lower thread numbers for a given sync frame shall be delivered first to the decoder under loss-free and
S:1位表示数据包内容用于同步帧的位。使用VRC的编码器可以发送同一“同步”图片的多个表示，以确保无论哪个图片线程被错误或数据包丢失损坏，都可以确保接收特定图片的至少一个表示（在至少一个线程内）。然后，同步图片可用于预测任何线程。如果没有发生数据包丢失，则可以使用线程0的同步帧内容，并丢弃其他线程的同步帧内容（对于其他线程也是如此）。线程0被认为是“规范”线程，使用它比使用其他线程更可取。具有较低线程编号的数据包的内容应被视为具有比具有较高线程编号的数据包更高的处理和交付优先级。因此，对于给定的同步帧，具有较低线程号的数据包应首先在无丢失和无延迟的情况下交付给解码器
low-time-jitter conditions, which will result in the discarding of the sync contents of the higher-numbered threads as specified in Annex N of [4].
低时间抖动条件，这将导致丢弃[4]附录N中规定的编号较高线程的同步内容。
A picture segment packet is defined as a packet that starts at the location of a Picture, GOB, or slice start code in the H.263+ data stream. This corresponds to the definition of the start of a video picture segment as defined in H.263+. For such packets, P=1 always.
图片段分组被定义为在H.263+数据流中的图片、GOB或片段开始代码的位置开始的分组。这对应于H.263+中定义的视频图片段开始的定义。对于此类数据包，P始终为1。
An extra picture header can sometimes be attached in the payload header of such packets. Whenever an extra picture header is attached as signified by PLEN>0, only the last six bits of its picture start code, '100000', are included in the payload header. A complete H.263+ picture header with byte aligned picture start code can be conveniently assembled on the receiving end by prepending the sixteen leading '0' bits.
有时可以在此类分组的有效负载报头中附加额外图片报头。每当附加一个额外的图片头时，如PLEN>0所示，有效负载头中只包括其图片开始代码“100000”的最后六位。一个完整的H.263+图片头，带有字节对齐的图片开始代码，可以通过在16个前导“0”位前加前缀方便地在接收端组装。
When PLEN>0, the end bit position corresponding to the last byte of the picture header data is indicated by PEBIT. The actual bitstream data shall begin on an 8-bit byte boundary following the payload header.
当PLEN>0时，与图片标题数据的最后一个字节相对应的结束位位置由PEBIT指示。实际比特流数据应在有效负载报头之后的8位字节边界上开始。
A sequence ending packet is defined as a packet that starts at the location of an EOS or EOSBS code in the H.263+ data stream. This delineates the end of a sequence of H.263+ video data (more H.263+ video data may still follow later, however, as specified in ITU-T Recommendation H.263). For such packets, P=1 and PLEN=0 always.
序列结束分组被定义为在H.263+数据流中的EOS或EOSBS代码的位置开始的分组。这描绘了H.263+视频数据序列的结束（然而，如ITU-T建议H.263中所规定的，更多H.263+视频数据稍后仍可能跟随）。对于这样的数据包，P=1和PLEN=0总是存在的。
The optional header extension for VRC may or may not be present as indicated by the V bit flag.
如V位标志所示，VRC的可选标头扩展可能存在，也可能不存在。
Any packet that contains the whole or the start of a coded picture shall start at the location of the picture start code (PSC), and should normally be encapsulated with no extra copy of the picture header. In other words, normally PLEN=0 in such a case. However, if the coded picture contains an incomplete picture header (UFEP = "000"), then a representation of the complete (UFEP = "001") picture header may be attached during packetization in order to provide greater error resilience. Thus, for packets that start at the location of a picture start code, PLEN shall be zero unless both of the following conditions apply:
包含编码图片的全部或开头的任何数据包应在图片开始代码（PSC）的位置开始，并且通常应在没有额外图片标题副本的情况下进行封装。换言之，在这种情况下，通常PLEN=0。然而，如果编码图片包含不完整的图片标题（UFEP=“000”），则在打包期间可以附加完整（UFEP=“001”）图片标题的表示，以提供更大的错误恢复能力。因此，对于在图片开始代码位置开始的数据包，除非以下两个条件都适用，否则PLEN应为零：
1) The picture header in the H.263+ bitstream payload is incomplete (PLUSPTYPE present and UFEP="000"), and
1) H.263+比特流有效负载中的图片标头不完整（PLUSPTYPE present和UFEP=“000”），并且
2) The additional picture header which is attached is not incomplete (UFEP="001").
2) 附加的图片标题并非不完整（UFEP=“001”）。
A packet which begins at the location of a Picture, GOB, slice, EOS, or EOSBS start code shall omit the first two (all zero) bytes from the H.263+ bitstream, and signify their presence by setting P=1 in the payload header.
从图片、GOB、切片、EOS或EOSBS开始代码位置开始的数据包应省略H.263+比特流中的前两个（全部为零）字节，并通过在有效负载报头中设置P=1表示其存在。
Here is an example of encapsulating the first packet in a frame (without an attached redundant complete picture header):
这里是将第一分组封装在帧中（没有附加的冗余完整图片报头）的示例：
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |1|V|0|0|0|0|0|0|0|0|0| bitstream data without the |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| first two 0 bytes of the PSC ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |1|V|0|0|0|0|0|0|0|0|0| bitstream data without the |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| first two 0 bytes of the PSC ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For a packet that begins at the location of a GOB or slice start code, PLEN may be zero or may be nonzero, depending on whether a redundant picture header is attached to the packet. In environments with very low packet loss rates, or when picture header contents are very seldom likely to change (except as can be detected from the GFID syntax of H.263+), a redundant copy of the picture header is not required. However, in less ideal circumstances a redundant picture header should be attached for enhanced error resilience, and its presence is indicated by PLEN>0.
对于在GOB或切片开始代码位置开始的数据包，PLEN可能为零或非零，这取决于是否将冗余图片报头附加到该数据包。在数据包丢失率非常低的环境中，或者当图片标题内容很少可能发生变化时（除非可以从H.263+的GFID语法中检测到），不需要图片标题的冗余副本。但是，在不太理想的情况下，应附加冗余图片标题以增强错误恢复能力，其存在由PLEN>0表示。
Assuming a PLEN of 9 and P=1, below is an example of a packet that begins with a byte aligned GBSC or a SSC:
假设PLEN为9且P=1，下面是以字节对齐的GBSC或SSC开头的数据包示例：
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |1|V|0 0 1 0 0 1|PEBIT|1 0 0 0 0 0| picture header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| starting with TR, PTYPE ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | bitstream |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data starting with GBSC/SSC without its first two 0 bytes ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |1|V|0 0 1 0 0 1|PEBIT|1 0 0 0 0 0| picture header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| starting with TR, PTYPE ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | bitstream |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data starting with GBSC/SSC without its first two 0 bytes ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Notice that only the last six bits of the picture start code, '100000', are included in the payload header. A complete H.263+ picture header with byte aligned picture start code can be conveniently assembled if needed on the receiving end by prepending the sixteen leading '0' bits.
请注意，只有图片开始代码的最后六位“100000”包含在有效负载标头中。如果需要，可以在接收端通过预加16个前导“0”位，方便地组装带有字节对齐图片开始代码的完整H.263+图片报头。
For a packet that begins with an EOS or EOSBS code, PLEN shall be zero, and no Picture, GOB, or Slice start codes shall be included within the same packet. As with other packets beginning with start codes, the two all-zero bytes that begin the EOS or EOSBS code at the beginning of the packet shall be omitted, and their presence shall be indicated by setting the P bit to 1 in the payload header.
对于以EOS或EOSBS代码开头的数据包，PLEN应为零，且同一数据包中不得包含图片、GOB或切片开始代码。与以开始代码开始的其他数据包一样，应省略在数据包开始处开始EOS或EOSBS代码的两个全零字节，并且应通过在有效负载报头中将P位设置为1来指示其存在。
System designers should be aware that some decoders may interpret the loss of a packet containing only EOS or EOSBS information as the loss of essential video data and may thus respond by not displaying some subsequent video information. Since EOS and EOSBS codes do not actually affect the decoding of video pictures, they are somewhat unnecessary to send at all. Because of the danger of misinterpretation of the loss of such a packet (which can be detected by the sequence number), encoders are generally to be discouraged from sending EOS and EOSBS.
系统设计者应当意识到，一些解码器可能将仅包含EOS或EOSB信息的分组的丢失解释为基本视频数据的丢失，并且因此可能通过不显示一些后续视频信息来响应。由于EOS和EOSBS代码实际上并不影响视频图片的解码，因此根本不需要发送它们。由于这种分组的丢失（可通过序列号检测到）有被误解的危险，通常不鼓励编码器发送EOS和EOSB。
Below is an example of a packet containing an EOS code:
下面是包含EOS代码的数据包示例：
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |1|V|0|0|0|0|0|0|0|0|0|1|1|1|1|1|1|0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |1|V|0|0|0|0|0|0|0|0|0|1|1|1|1|1|1|0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.2 Encapsulating Follow-On Packet (P=0)
5.2 封装后续数据包（P=0）
A Follow-on packet contains a number of bytes of coded H.263+ data which does not start at a synchronization point. That is, a Follow-On packet does not start with a Picture, GOB, Slice, EOS, or EOSBS header, and it may or may not start at a macroblock boundary. Since Follow-on packets do not start at synchronization points, the data at the beginning of a follow-on packet is not independently decodable. For such packets, P=0 always. If the preceding packet of a Follow-on packet got lost, the receiver may discard that Follow-on packet as well as all other following Follow-on packets. Better behavior, of course, would be for the receiver to scan the interior of the packet payload content to determine whether any start codes are found in the interior of the packet which can be used as resync points. The use of an attached copy of a picture header for a follow-on packet is
后续数据包包含许多字节的编码H.263+数据，这些数据不从同步点开始。也就是说，后续分组不以图片、GOB、切片、EOS或EOSBS报头开始，并且它可以也可以不以宏块边界开始。由于后续数据包不在同步点开始，因此后续数据包开始处的数据不可独立解码。对于此类数据包，P始终为0。如果后续分组的前一分组丢失，则接收机可以丢弃该后续分组以及所有其他后续分组。当然，更好的行为将是接收器扫描数据包有效载荷内容的内部，以确定是否在数据包内部找到任何可以用作重新同步点的开始代码。为后续数据包使用图片标题的附加副本是必要的
useful only if the interior of the packet or some subsequent follow-on packet contains a resync code such as a GOB or slice start code. PLEN>0 is allowed, since it may allow resync in the interior of the packet. The decoder may also be resynchronized at the next segment or picture packet.
仅当数据包或某些后续数据包的内部包含重新同步代码（如GOB或切片开始代码）时才有用。允许PLEN>0，因为它可能允许在数据包内部重新同步。解码器还可以在下一段或图片分组处重新同步。
Here is an example of a follow-on packet (with PLEN=0):
以下是后续数据包的示例（PLEN=0）：
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |0|V|0|0|0|0|0|0|0|0|0| bitstream data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR |0|V|0|0|0|0|0|0|0|0|0| bitstream data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
There is no syntactical difference between a picture segment packet and a Follow-on packet, other than the indication P=1 for picture segment or sequence ending packets and P=0 for Follow-on packets. See the following for a summary of the entire packet types and ways to distinguish between them.
图片段分组和后续分组之间没有语法上的差异，除了图片段或序列结束分组的指示P＝1和后续分组的指示P＝0之外。有关整个数据包类型的摘要以及区分它们的方法，请参见以下内容。
It is possible to distinguish between the different packet types by checking the P bit and the first 6 bits of the payload along with the header information. The following table shows the packet type for permutations of this information (see also the picture/GOB/Slice header descriptions in H.263+ for details):
通过检查有效载荷的P位和前6位以及报头信息，可以区分不同的分组类型。下表显示了该信息排列的数据包类型（详见H.263+中的picture/GOB/Slice头描述）：
--------------+--------------+----------------------+-------------------
First 6 bits | P-Bit | PLEN | Packet | Remarks
of Payload |(payload hdr.)| |
--------------+--------------+----------------------+-------------------
100000 | 1 | 0 | Picture | Typical Picture
100000 | 1 | > 0 | Picture | Note UFEP
1xxxxx | 1 | 0 | GOB/Slice/EOS/EOSBS | See possible GNs
1xxxxx | 1 | > 0 | GOB/Slice | See possible GNs
Xxxxxx | 0 | 0 | Follow-on |
Xxxxxx | 0 | > 0 | Follow-on | Interior Resync
--------------+--------------+----------------------+-------------------
--------------+--------------+----------------------+-------------------
First 6 bits | P-Bit | PLEN | Packet | Remarks
of Payload |(payload hdr.)| |
--------------+--------------+----------------------+-------------------
100000 | 1 | 0 | Picture | Typical Picture
100000 | 1 | > 0 | Picture | Note UFEP
1xxxxx | 1 | 0 | GOB/Slice/EOS/EOSBS | See possible GNs
1xxxxx | 1 | > 0 | GOB/Slice | See possible GNs
Xxxxxx | 0 | 0 | Follow-on |
Xxxxxx | 0 | > 0 | Follow-on | Interior Resync
--------------+--------------+----------------------+-------------------
The details regarding the possible values of the five bit Group Number (GN) field which follows the initial "1" bit when the P-bit is "1" for a GOB, Slice, EOS, or EOSBS packet are found in section 5.2.3 of [4].
当GOB、切片、EOS或EOSBS数据包的P位为“1”时，初始“1”位之后的五位组号（GN）字段可能值的详细信息见[4]第5.2.3节。
As defined in this specification, every start of a coded frame (as indicated by the presence of a PSC) has to be encapsulated as a picture segment packet. If the whole coded picture fits into one
如本规范中所定义，编码帧的每个开始（如PSC的存在所示）必须封装为图片段分组。如果整个编码的图片适合一个
packet of reasonable size (which is dependent on the connection characteristics), this is the only type of packet that may need to be used. Due to the high compression ratio achieved by H.263+ it is often possible to use this mechanism, especially for small spatial picture formats such as QCIF and typical Internet packet sizes around 1500 bytes.
合理大小的数据包（取决于连接特性），这是可能需要使用的唯一数据包类型。由于H.263+实现的高压缩比，通常可以使用这种机制，特别是对于小空间图片格式，如QCIF和大约1500字节的典型互联网数据包大小。
If the complete coded frame does not fit into a single packet, two different ways for the packetization may be chosen. In case of very low or zero packet loss probability, one or more Follow-on packets may be used for coding the rest of the picture. Doing so leads to minimal coding and packetization overhead as well as to an optimal use of the maximal packet size, but does not provide any added error resilience.
如果完整的编码帧不适合单个分组，则可以选择两种不同的分组方式。在包丢失概率非常低或为零的情况下，可以使用一个或多个后续包对图片的其余部分进行编码。这样做将导致最小的编码和分组开销以及最大分组大小的最佳使用，但不会提供任何额外的错误恢复能力。
The alternative is to break the picture into reasonably small partitions - called Segments - (by using the Slice or GOB mechanism), that do offer synchronization points. By doing so and using the Picture Segment payload with PLEN>0, decoding of the transmitted packets is possible even in such cases in which the Picture packet containing the picture header was lost (provided any necessary reference picture is available). Picture Segment packets can also be used in conjunction with Follow-on packets for large segment sizes.
另一种方法是将图片分成相当小的分区（称为段）（通过使用Slice或GOB机制），这些分区确实提供了同步点。通过这样做并使用具有PLEN>0的图片段有效载荷，即使在包含图片报头的图片分组丢失的情况下（前提是任何必要的参考图片可用），也可以对发送的分组进行解码。图片段数据包也可以与后续数据包一起用于较大的数据段大小。
RTP packets using the payload format defined in this specification are subject to the security considerations discussed in the RTP specification [1], and any appropriate RTP profile (for example [2]). This implies that confidentiality of the media streams is achieved by encryption. Because the data compression used with this payload format is applied end-to-end, encryption may be performed after compression so there is no conflict between the two operations.
使用本规范中定义的有效负载格式的RTP数据包受RTP规范[1]和任何适当RTP配置文件（例如[2]）中讨论的安全注意事项的约束。这意味着媒体流的机密性是通过加密实现的。由于与此有效负载格式一起使用的数据压缩是端到端应用的，因此可以在压缩之后执行加密，因此两个操作之间没有冲突。
A potential denial-of-service threat exists for data encodings using compression techniques that have non-uniform receiver-end computational load. The attacker can inject pathological datagrams into the stream which are complex to decode and cause the receiver to be overloaded. However, this encoding does not exhibit any significant non-uniformity.
使用压缩技术的数据编码存在潜在的拒绝服务威胁，这种压缩技术具有非均匀的接收端计算负载。攻击者可以向流中注入病理数据报，这些数据报解码复杂，并导致接收器过载。然而，这种编码并没有表现出任何显著的非均匀性。
As with any IP-based protocol, in some circumstances a receiver may be overloaded simply by the receipt of too many packets, either desired or undesired. Network-layer authentication may be used to discard packets from undesired sources, but the processing cost of the authentication itself may be too high. In a multicast
与任何基于IP的协议一样，在某些情况下，接收机可能仅仅因为接收了太多的数据包而过载，不管是想要的还是不想要的。网络层认证可用于丢弃来自不希望的源的数据包，但认证本身的处理成本可能过高。在多播中
environment, pruning of specific sources may be implemented in future versions of IGMP [5] and in multicast routing protocols to allow a receiver to select which sources are allowed to reach it.
在环境中，特定源的修剪可以在IGMP[5]的未来版本和多播路由协议中实现，以允许接收器选择允许到达它的源。
A security review of this payload format found no additional considerations beyond those in the RTP specification.
对该有效负载格式的安全性审查发现，除了RTP规范中的考虑之外，没有其他考虑。
Carsten Bormann
Universitaet Bremen FB3 TZI EMail: cabo@tzi.org
Postfach 330440 Phone: +49.421.218-7024
D-28334 Bremen, GERMANY Fax: +49.421.218-7000
Carsten Bormann
Universitaet Bremen FB3 TZI EMail: cabo@tzi.org
Postfach 330440 Phone: +49.421.218-7024
D-28334 Bremen, GERMANY Fax: +49.421.218-7000
Linda Cline
Intel Corp. M/S JF3-206 EMail: lscline@jf.intel.com
2111 NE 25th Avenue Phone: +1 503 264 3501
Hillsboro, OR 97124, USA Fax: +1 503 264 3483
Linda Cline
Intel Corp. M/S JF3-206 EMail: lscline@jf.intel.com
2111 NE 25th Avenue Phone: +1 503 264 3501
Hillsboro, OR 97124, USA Fax: +1 503 264 3483
Gim Deisher
Intel Corp. M/S JF2-78 EMail: gim.l.deisher@intel.com
2111 NE 25th Avenue Phone: +1 503 264 3758
Hillsboro, OR 97124, USA Fax: +1 503 264 9372
Gim Deisher
Intel Corp. M/S JF2-78 EMail: gim.l.deisher@intel.com
2111 NE 25th Avenue Phone: +1 503 264 3758
Hillsboro, OR 97124, USA Fax: +1 503 264 9372
Tom Gardos
Intel Corp. M/S JF2-78 EMail: thomas.r.gardos@intel.com
2111 NE 25th Avenue Phone: +1 503 264 6459
Hillsboro, OR 97124, USA Fax: +1 503 264 9372
Tom Gardos
Intel Corp. M/S JF2-78 EMail: thomas.r.gardos@intel.com
2111 NE 25th Avenue Phone: +1 503 264 6459
Hillsboro, OR 97124, USA Fax: +1 503 264 9372
Christian Maciocco
Intel Corp. M/S JF3-206 EMail: christian.maciocco@intel.com
2111 NE 25th Avenue Phone: +1 503 264 1770
Hillsboro, OR 97124, USA Fax: +1 503 264 9428
Christian Maciocco
Intel Corp. M/S JF3-206 EMail: christian.maciocco@intel.com
2111 NE 25th Avenue Phone: +1 503 264 1770
Hillsboro, OR 97124, USA Fax: +1 503 264 9428
Donald Newell
Intel Corp. M/S JF3-206 EMail: donald.newell@intel.com
2111 NE 25th Avenue Phone: +1 503 264 9234
Hillsboro, OR 97124, USA Fax: +1 503 264 9428
Donald Newell
Intel Corp. M/S JF3-206 EMail: donald.newell@intel.com
2111 NE 25th Avenue Phone: +1 503 264 9234
Hillsboro, OR 97124, USA Fax: +1 503 264 9428
Joerg Ott
Universitaet Bremen FB3 TZI EMail: jo@tzi.org
Postfach 330440 Phone: +49.421.218-7024
D-28334 Bremen, GERMANY Fax: +49.421.218-7000
Joerg Ott
Universitaet Bremen FB3 TZI EMail: jo@tzi.org
Postfach 330440 Phone: +49.421.218-7024
D-28334 Bremen, GERMANY Fax: +49.421.218-7000
Gary Sullivan
PictureTel Corp. M/S 635 EMail: garys@pictel.com
100 Minuteman Road Phone: +1 978 623 4324
Andover, MA 01810, USA Fax: +1 978 749 2804
Gary Sullivan
PictureTel Corp. M/S 635 EMail: garys@pictel.com
100 Minuteman Road Phone: +1 978 623 4324
Andover, MA 01810, USA Fax: +1 978 749 2804
Stephan Wenger
Technische Universitaet Berlin FB13
Sekr. FR 6-3 EMail: stewe@cs.tu-berlin.de
Franklinstr. 28/29 Phone: +49.30.314-73160
D-10587 Berlin, GERMANY Fax: +49.30.314-25156
Stephan Wenger
Technische Universitaet Berlin FB13
Sekr. FR 6-3 EMail: stewe@cs.tu-berlin.de
Franklinstr. 28/29 Phone: +49.30.314-73160
D-10587 Berlin, GERMANY Fax: +49.30.314-25156
Chad Zhu
Intel Corp. M/S JF3-202 EMail: czhu@ix.netcom.com
2111 NE 25th Avenue Phone: +1 503 264 6004
Hillsboro, OR 97124, USA Fax: +1 503 264 1805
Chad Zhu
Intel Corp. M/S JF3-202 EMail: czhu@ix.netcom.com
2111 NE 25th Avenue Phone: +1 503 264 6004
Hillsboro, OR 97124, USA Fax: +1 503 264 1805
[1] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP : A Transport Protocol for Real-Time Applications", RFC 1889, January 1996.
[1] Schulzrinne，H.，Casner，S.，Frederick，R.，和V.Jacobson，“RTP：实时应用的传输协议”，RFC 1889，1996年1月。
[2] Schulzrinne, H., "RTP Profile for Audio and Video Conference with Minimal Control", RFC 1890, January 1996.
[2] Schulzrinne，H.，“具有最小控制的音频和视频会议的RTP配置文件”，RFC 1890，1996年1月。
[3] "Video Coding for Low Bit Rate Communication," ITU-T Recommendation H.263, March 1996.
[3] “低比特率通信的视频编码”，ITU-T建议H.263，1996年3月。
[4] "Video Coding for Low Bit Rate Communication," ITU-T Recommendation H.263, January 1998.
[4] “低比特率通信的视频编码”，ITU-T建议H.263，1998年1月。
[5] Turletti, T. and C. Huitema, "RTP Payload Format for H.261 Video Streams", RFC 2032, October 1996.
[5] Turletti，T.和C.Huitema，“H.261视频流的RTP有效载荷格式”，RFC 2032，1996年10月。
[6] Zhu, C., "RTP Payload Format for H.263 Video Streams", RFC 2190, September 1997.
[6] 朱，C，“H.263视频流的RTP有效载荷格式”，RFC 2190，1997年9月。
[7] S. Wenger, "Video Redundancy Coding in H.263+," Proc. Audio-Visual Services over Packet Networks, Aberdeen, U.K., September 1997.
[7] S.Wenger，“H.263+中的视频冗余编码”，Proc。在分组网络上的视听服务，阿伯丁，英国，1997年9月。
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