Internet Engineering Task Force (IETF) R. Huang
Request for Comments: 7867 Huawei
Category: Standards Track July 2016
ISSN: 2070-1721
Internet Engineering Task Force (IETF) R. Huang
Request for Comments: 7867 Huawei
Category: Standards Track July 2016
ISSN: 2070-1721
RTP Control Protocol (RTCP) Extended Report (XR) Block for Loss Concealment Metrics for Video Applications
用于视频应用丢失隐藏度量的RTP控制协议（RTCP）扩展报告（XR）块
Abstract
摘要
This document defines a new RTP Control Protocol (RTCP) Extended Report (XR) block that allows the reporting of loss concealment metrics for video applications of RTP.
本文档定义了一个新的RTP控制协议（RTCP）扩展报告（XR）块，该块允许报告RTP视频应用的丢失隐藏度量。
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 7841.
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 7841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/rfc7867.
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/rfc7867.
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 ....................................................2
1.1. RTCP and RTCP XR Reports ...................................3
1.2. Performance Metrics Framework ..............................3
1.3. Applicability ..............................................3
2. Terminology .....................................................3
3. Video Loss Concealment Methods ..................................3
4. Video Loss Concealment Report Block .............................4
5. SDP Signaling ...................................................8
5.1. SDP rtcp-xr-attrib Attribute Extension .....................8
5.2. Offer/Answer Usage .........................................9
6. Security Considerations .........................................9
7. IANA Considerations .............................................9
7.1. New RTCP XR Block Type Value ...............................9
7.2. New RTCP XR SDP Parameter ..................................9
7.3. Contact Information for Registrations .....................10
8. References .....................................................10
8.1. Normative References ......................................10
8.2. Informative References ....................................11
Appendix A. Metrics Represented Using the Template from RFC 6390 ..12
Acknowledgements ..................................................16
Authors' Addresses ................................................16
1. Introduction ....................................................2
1.1. RTCP and RTCP XR Reports ...................................3
1.2. Performance Metrics Framework ..............................3
1.3. Applicability ..............................................3
2. Terminology .....................................................3
3. Video Loss Concealment Methods ..................................3
4. Video Loss Concealment Report Block .............................4
5. SDP Signaling ...................................................8
5.1. SDP rtcp-xr-attrib Attribute Extension .....................8
5.2. Offer/Answer Usage .........................................9
6. Security Considerations .........................................9
7. IANA Considerations .............................................9
7.1. New RTCP XR Block Type Value ...............................9
7.2. New RTCP XR SDP Parameter ..................................9
7.3. Contact Information for Registrations .....................10
8. References .....................................................10
8.1. Normative References ......................................10
8.2. Informative References ....................................11
Appendix A. Metrics Represented Using the Template from RFC 6390 ..12
Acknowledgements ..................................................16
Authors' Addresses ................................................16
Multimedia applications often suffer from packet losses in IP networks. In order to get a reasonable degree of quality when there is packet loss, it is necessary to have loss concealment mechanisms at the decoder. Video loss concealment is a range of techniques to mask the effects of packet loss in video communications.
多媒体应用在IP网络中经常遭受数据包丢失。为了在存在分组丢失时获得合理程度的质量，有必要在解码器处具有丢失隐藏机制。视频丢失隐藏是在视频通信中掩盖数据包丢失影响的一系列技术。
In some applications, reporting the information of receivers applying video loss concealment could give monitors or senders useful information on the Quality of Experience (QoE) of the application. One example is no-reference video quality evaluation. Video probes located upstream from the video endpoint or terminal may not see loss occurring between the probe and the endpoint, and also may not be fully aware of the specific loss concealment methods being dynamically applied by the video endpoint. Evaluating error concealment is important in this circumstance to estimate the subjective impact of impairments.
在一些应用中，报告应用视频丢失隐藏的接收器的信息可以为监视器或发送者提供有关应用的体验质量（QoE）的有用信息。一个例子是无参考视频质量评估。位于视频端点或终端上游的视频探针可能看不到探针和端点之间发生的丢失，并且也可能不完全知道视频端点动态应用的特定丢失隐藏方法。在这种情况下，评估错误隐藏对于评估损害的主观影响非常重要。
This document defines one new block type for video loss concealment to augment those defined in [RFC3611] and [RFC7294] for use in a range of RTP video applications. The metrics defined in this document belong to the class of transport-related terminal metrics defined in [RFC6792].
本文件为视频丢失隐藏定义了一种新的块类型，以扩充[RFC3611]和[RFC7294]中定义的块类型，以便在一系列RTP视频应用中使用。本文件中定义的指标属于[RFC6792]中定义的运输相关终端指标类别。
The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] defines an extensible structure for reporting using an RTCP Extended Report (XR). This document defines a new Extended Report block that is used as defined in [RFC3550] and [RFC3611].
[RFC3550]中定义了使用RTCP进行报告。[RFC3611]定义了使用RTCP扩展报告（XR）进行报告的可扩展结构。本文档定义了一个新的扩展报告块，该报告块按照[RFC3550]和[RFC3611]中的定义使用。
The Performance Metrics Framework [RFC6390] provides guidance on the definition and specification of performance metrics. The RTP monitoring framework [RFC6792] provides guidelines for the reporting block format using RTCP XR. The XR block type described in this document is in accordance with the guidelines in [RFC6390] and [RFC6792].
性能指标框架[RFC6390]提供了有关性能指标定义和规范的指导。RTP监控框架[RFC6792]提供了使用RTCP XR的报告块格式指南。本文档中描述的XR块类型符合[RFC6390]和[RFC6792]中的指南。
These metrics are applicable to video applications the video component of audio/video applications using RTP and applying packet loss concealment mechanisms that are incorporated into the receiving endpoint to mitigate the impact of network impairments on QoE. For example, in an IPTV system, set-top boxes could use this RTCP XR block to report loss and loss concealment metrics to an IPTV management system to enable the service provider to monitor the quality of the IPTV service being delivered to end users.
这些指标适用于视频应用——使用RTP的音频/视频应用的视频组件，并应用并入接收端点的分组丢失隐藏机制，以减轻网络损伤对QoE的影响。例如，在IPTV系统中，机顶盒可以使用该RTCP XR块向IPTV管理系统报告丢失和丢失隐藏度量，以使服务提供商能够监控交付给最终用户的IPTV服务的质量。
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。
Video loss concealment mechanisms can be classified into 4 types as follows:
视频丢失隐藏机制可分为以下4种类型：
a) Frame freeze
a) 定格
The impaired video frame is not displayed; instead, the previously displayed frame is frozen for the duration of the loss event.
受损视频帧不显示；相反，先前显示的帧在丢失事件期间被冻结。
b) Interframe extrapolation
b) 帧间外推
If an area of the video frame is damaged by loss, the same area from the previous frame(s) can be used to estimate what the missing pixels would have been. This can work well in a scene
如果视频帧的某个区域因丢失而损坏，则可以使用前一帧的相同区域来估计丢失的像素。这可以在场景中很好地工作
with no motion but can be very noticeable if there is significant movement from one frame to another. Simple decoders can simply reuse the pixels that were in the missing area, while more complex decoders can try to use several frames to do a more complex extrapolation. Another example of a sophisticated form of interframe repair is to estimate the motion of the damaged region based on the motion of surrounding regions, and use that to select what part of the previous frame to use for repair. Some important frames, such as Instantaneous Decoding Refresh (IDR) frames, may not depend on any other frames and may be involved in a scene change. Using the interframe extrapolation method to conceal the loss of these frames may not obtain a satisfactory result.
没有运动，但如果从一帧到另一帧有显著的运动，则会非常明显。简单的解码器可以简单地重用丢失区域中的像素，而更复杂的解码器可以尝试使用多个帧来进行更复杂的外推。帧间修复的复杂形式的另一个例子是基于周围区域的运动估计受损区域的运动，并使用该运动来选择前一帧的哪个部分用于修复。一些重要帧，例如瞬时解码刷新（IDR）帧，可能不依赖于任何其他帧，并且可能涉及场景更改。使用帧间外推方法来隐藏这些帧的丢失可能无法获得令人满意的结果。
c) Interpolation
c) 插值
A decoder uses the undamaged pixels in the video frame to estimate what the missing block of pixels should have.
解码器使用视频帧中未损坏的像素来估计丢失的像素块应该有什么。
d) Error-resilient encoding
d) 容错编码
The sender encodes the message in a redundant way so that the receiver can correct errors using the redundant information. There are usually two kinds of error-resilient encoding: One is that the redundant data useful for error resiliency performed at the decoder can be embedded into the compressed image/video bitstream. The other is encoding at the bitstream level, e.g., Forward Error Correction (FEC).
发送方以冗余方式对消息进行编码，以便接收方可以使用冗余信息纠正错误。通常有两种容错编码：一种是在解码器处执行的用于容错的冗余数据可以嵌入到压缩的图像/视频比特流中。另一种是在比特流级别编码，例如，前向纠错（FEC）。
Usually, methods b, c, and d are deployed together to provide comprehensive loss concealment in complex decoders, while method a is relatively independent and may be applied in some simple decoders. Moreover, the frame-freeze method repairs video based on frames, while the other methods repair video based on fine-grained elements, such as macroblocks or bitstreams; this will cause the measurement metrics of frame-freeze and the other methods to be slightly different. Thus, In this document, we differentiate between frame-freeze and the other 3 loss concealment mechanisms.
通常，方法b、c和d一起部署以在复杂解码器中提供全面的丢失隐藏，而方法a相对独立，可以应用于一些简单解码器。此外，帧冻结方法基于帧修复视频，而其他方法基于细粒度元素（例如宏块或比特流）修复视频；这将导致帧冻结和其他方法的测量指标略有不同。因此，在本文中，我们区分了帧冻结和其他3种丢失隐藏机制。
This block reports the video loss concealment metrics to complement the audio metrics defined in [RFC7294]. The report block MUST be sent in conjunction with the information from the Measurement Information Block [RFC6776]. Instances of this metric block refer by synchronization source (SSRC) to the separate auxiliary Measurement Information Block [RFC6776]. The Video Loss Concealment Report Block relies on the measurement period in the Measurement Information Block indicating the span of the report. If the measurement period is not
此块报告视频丢失隐藏度量，以补充[RFC7294]中定义的音频度量。报告块必须与测量信息块[RFC6776]中的信息一起发送。此度量块的实例通过同步源（SSRC）指向单独的辅助测量信息块[RFC6776]。视频丢失隐藏报告块依赖于测量信息块中指示报告范围的测量周期。如果测量周期不是
received in the same compound RTCP packet as this metric block, this metric block MUST be discarded at the receiving side. The metrics in this report block are based on measurements that are typically made at the time that a video frame is decoded and rendered for playout.
在与此度量块相同的复合RTCP数据包中接收，必须在接收端丢弃此度量块。此报告块中的度量基于通常在视频帧解码和渲染以进行播放时进行的测量。
The Video Loss Concealment Report Block has the following format:
视频丢失隐藏报告块具有以下格式：
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=34 | I | V | RSV | Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Impaired Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Concealed Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mean Frame Freeze Duration (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MIFP | MCFP | FFSC | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=34 | I | V | RSV | Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Impaired Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Concealed Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mean Frame Freeze Duration (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MIFP | MCFP | FFSC | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format for the Video Loss Concealment Report Block
图1：视频丢失隐藏报告块的格式
Block Type (BT): 8 bits
块类型（BT）：8位
A Video Loss Concealment Report Block is identified by the constant 34.
视频丢失隐藏报告块由常数34标识。
Interval Metric Flag (I): 2 bits
间隔度量标志（I）：2位
This field indicates whether the reported metrics are interval, cumulative, or sampled metrics [RFC6792]:
此字段指示报告的度量是间隔度量、累积度量还是采样度量[RFC6792]：
I=10: Interval Duration - the reported value applies to the most recent measurement interval duration between successive metrics reports.
I=10：间隔持续时间-报告值适用于连续度量报告之间的最新度量间隔持续时间。
I=11: Cumulative Duration - the reported value applies to the accumulation period characteristic of cumulative measurements.
I=11：累积持续时间-报告值适用于累积测量的累积周期特征。
I=01: Sampled Value - this value MUST NOT be used for this block type.
I=01：采样值-此值不得用于此块类型。
I=00: Reserved.
I=00：保留。
Video Loss Concealment Method Type (V): 2 bits
视频丢失隐藏方法类型（V）：2位
This field is used to identify the video loss concealment method type used at the receiver. The value is defined as follows:
此字段用于识别接收器使用的视频丢失隐藏方法类型。该值定义如下：
V=10: Frame-freeze
V=11: Other Loss Concealment Method
V=01 and V=00: Reserved
V=10: Frame-freeze
V=11: Other Loss Concealment Method
V=01 and V=00: Reserved
If frame-freeze and another loss concealment method are used together for the media stream, two report blocks (one with V=10 for frame freeze and one with V=11 for the other loss concealment method) SHOULD be compounded together to report complete concealment information.
如果媒体流同时使用帧冻结和另一种丢失隐藏方法，则应将两个报告块（一个用于帧冻结，一个用于另一种丢失隐藏方法，一个用于V=11）组合在一起，以报告完整的隐藏信息。
RSV: 4 bits
RSV:4位
These bits are reserved for future use. They MUST be set to zero by senders and ignored by receivers (see Section 4.2 of [RFC6709]).
这些位留作将来使用。发送方必须将其设置为零，接收方必须忽略（见[RFC6709]第4.2节）。
Block Length: 16 bits
块长度：16位
This field is in accordance with the definition in [RFC3611]. In this report block, it MUST be set to 5 when V=10 and set to 4 when V=11. The block MUST be discarded if the block length is set to a different value.
该字段符合[RFC3611]中的定义。在此报告块中，当V=10时必须将其设置为5，当V=11时必须将其设置为4。如果块长度设置为不同的值，则必须丢弃该块。
SSRC of Source: 32 bits
源的SSRC：32位
As defined in Section 4.1 of [RFC3611].
如[RFC3611]第4.1节所定义。
Impaired Duration: 32 bits
受损持续时间：32位
The total duration, expressed in units of RTP timestamp from the sending side of the reporting block, of video impaired by transmission loss before applying any loss concealment methods.
在应用任何丢失隐藏方法之前，受传输丢失损害的视频的总持续时间，以来自报告块的发送端的RTP时间戳为单位表示。
Two values are reserved: A value of 0xFFFFFFFE indicates out of range (that is, a measured value exceeding 0xFFFFFFFD), and a value of 0xFFFFFFFF indicates that the measurement is unavailable.
保留两个值：0xFFFFFE表示超出范围（即，测量值超过0xFFFFFD），0xFFFFFFFF表示测量不可用。
Concealed Duration: 32 bits
隐藏持续时间：32位
The total duration, expressed in units of RTP timestamp from the sending side of the reporting block, of concealed damaged video pictures on which the loss concealment method corresponding to the Video Loss Concealment Method Type is applied.
以来自报告块的发送侧的RTP时间戳为单位表示的、应用了与视频丢失隐藏方法类型对应的丢失隐藏方法的隐藏损坏视频图片的总持续时间。
Two values are reserved: A value of 0xFFFFFFFE indicates out of range (that is, a measured value exceeding 0xFFFFFFFD), and a value of 0xFFFFFFFF indicates that the measurement is unavailable.
保留两个值：0xFFFFFE表示超出范围（即，测量值超过0xFFFFFD），0xFFFFFFFF表示测量不可用。
Mean Frame-Freeze Duration: 32 bits
平均帧冻结持续时间：32位
Mean Frame-Freeze Duration is the mean duration, expressed in units of RTP timestamp from the sending side of the reporting block, of the frame-freeze events. The value of Mean Frame-Freeze Duration is calculated by summing the total duration of all frame freeze events and dividing by the number of events. This metric is optional. It only exists when Video Loss Concealment Method Type=10.
平均帧冻结持续时间是帧冻结事件的平均持续时间，以来自报告块的发送侧的RTP时间戳为单位表示。平均帧冻结持续时间的值通过将所有帧冻结事件的总持续时间相加并除以事件数来计算。此指标是可选的。仅当视频丢失隐藏方法类型=10时才存在。
Mean Impaired Frame Proportion (MIFP): 8 bits
平均受损帧比例（MIFP）：8位
Mean Impaired Frame Proportion is the mean proportion of each video frame impaired by loss before applying any loss concealment method during the interval, expressed as a fixed-point number with the binary point at the left edge of the field. It is calculated by summing the impaired proportion of each video frame and dividing by the number of frames during this period. The impaired proportion of each video frame is obtained by dividing the number of missing macroblocks from this video frame by the total macroblock number of the video frame, which is equivalent to multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.
平均受损帧比例是在间隔期间应用任何丢失隐藏方法之前，因丢失而受损的每个视频帧的平均比例，表示为固定点数，二进制点位于字段的左边缘。计算方法是将每个视频帧的受损比例相加，然后除以该期间的帧数。每个视频帧的受损比例是通过将该视频帧中缺失的宏块数除以视频帧的总宏块数获得的，这相当于将分割结果乘以256，将最大值限制为255（以避免溢出），并取整数部分。
If a video frame is totally lost, a value of 0xFF SHOULD be used for the frame when calculating the MIFP.
如果视频帧完全丢失，则在计算MIFP时，该帧应使用0xFF值。
Mean Concealed Frame Proportion (MCFP): 8 bits
平均隐藏帧比例（MCFP）：8位
Mean Concealed Frame Proportion is the mean proportion of each video frame to which loss concealment (depicted as "V" in the definition of "Video Loss Concealment Method Type") was applied during the interval, expressed as a fixed-point number with the binary point at the left edge of the field. It is calculated by summing the concealed proportion of each video frame and dividing by the number of frames during this period. The concealed proportion of each video frame is obtained by dividing the number of concealed macroblocks from this video frame by the total macroblock number of the video frame, which is equivalent to multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.
平均隐藏帧比例是在间隔期间应用丢失隐藏（在“视频丢失隐藏方法类型”的定义中描述为“V”）的每个视频帧的平均比例，表示为固定点数，二进制点位于字段的左边缘。计算方法是将每个视频帧的隐藏比例相加，然后除以该期间的帧数。每个视频帧的隐藏比例是通过将来自该视频帧的隐藏宏块的数量除以视频帧的总宏块数量来获得的，这相当于将分割结果乘以256，将最大值限制为255（以避免溢出），并取整数部分。
When calculating the MCFP, a value of 0xFF SHOULD be used for a lost frame that is totally concealed, and a value of 0 SHOULD be used for the frame if there are no concealed macroblocks in it. For Video Loss Concealment Method Type=10, each frame covered in the period of frame freeze is considered to be totally concealed; this means a value of 0xFF MUST be assigned.
在计算MCFP时，对于完全隐藏的丢失帧，应使用0xFF值，如果该帧中没有隐藏宏块，则应使用0值。对于视频丢失隐藏方法Type=10，帧冻结期间覆盖的每一帧视为完全隐藏；这意味着必须分配0xFF的值。
Fraction of Frames Subject to Concealment (FFSC): 8 bits
要隐藏的帧分数（FFSC）：8位
Fraction of Frames Subject to Concealment is calculated by dividing the number of frames to which loss concealment (using Video Loss Concealment Method Type) was applied by the total number of frames and expressing this value as a fixed-point number with the binary point at the left edge of the field. It is equivalent to multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.
通过将应用丢失隐藏（使用视频丢失隐藏方法类型）的帧数除以总帧数，并将该值表示为一个固定点数，二进制点位于字段左边缘，计算出需要隐藏的帧数分数。这相当于将除法的结果乘以256，将最大值限制为255（以避免溢出），并取整数部分。
A value of 0 indicates that there were no concealed frames, and a value of 0xFF indicates that the frames in the entire measurement interval are all concealed.
值为0表示没有隐藏帧，值为0xFF表示整个测量间隔内的帧都被隐藏。
Reserved: 8 bits
保留：8位
These bits are reserved for future use. They MUST be set to zero by senders and ignored by receivers (see Section 4.2 of [RFC6709]).
这些位留作将来使用。发送方必须将其设置为零，接收方必须忽略（见[RFC6709]第4.2节）。
[RFC3611] defines the use of the Session Description Protocol (SDP) for signaling the use of RTCP XR blocks.
[RFC3611]定义了会话描述协议（SDP）的使用，用于发送使用RTCP XR块的信号。
This session augments the SDP attribute "rtcp-xr" defined in Section 5.1 of [RFC3611] by providing an additional value of "xr-format" to signal the use of the report block defined in this document. The ABNF [RFC5234] syntax is as follows.
此会话通过提供附加值“xr format”来表示使用本文档中定义的报告块，从而增强[RFC3611]第5.1节中定义的SDP属性“rtcp xr”。ABNF[RFC5234]语法如下所示。
xr-format =/ xr-vlc-block
xr格式=/xr vlc块
xr-vlc-block = "vlc"
xr-vlc-block = "vlc"
When SDP is used in an offer/answer context, the SDP Offer/Answer usage defined in Section 5.2 of [RFC3611] for the unilateral "rtcp-xr" attribute parameters applies. For detailed usage of Offer/Answer for unilateral parameters, refer to Section 5.2 of [RFC3611].
当在报价/应答上下文中使用SDP时，[RFC3611]第5.2节中为单边“rtcp xr”属性参数定义的SDP报价/应答用法适用。有关单边参数的报价/应答的详细用法，请参阅[RFC3611]第5.2节。
It is believed that this RTCP XR block introduces no new security considerations beyond those described in [RFC3611]. This block does not provide per-packet statistics, so the risk to confidentiality documented in paragraph 3 of Section 7 of [RFC3611] does not apply.
据信，除了[RFC3611]中所述的安全注意事项外，该RTCP XR块未引入任何新的安全注意事项。该块不提供每包统计数据，因此[RFC3611]第7节第3段中记录的保密风险不适用。
An attacker is likely to put incorrect information in the Video Loss Concealment reports; this will affect the estimation of the performance of video loss concealment mechanisms and the QoE of users. Implementers SHOULD consider the guidance in [RFC7202] for using appropriate security mechanisms, i.e., where security is a concern, the implementation SHOULD apply encryption and authentication to the report block. For example, this can be achieved by using the AVPF profile together with the Secure RTP profile as defined in [RFC3711]; an appropriate combination of the two profiles (an "SAVPF") is specified in [RFC5124]. However, other mechanisms also exist (documented in [RFC7201]) and might be more suitable.
攻击者可能在视频丢失隐藏报告中输入错误信息；这将影响对视频丢失隐藏机制性能和用户QoE的估计。实现者应该考虑[RCF7202]中使用适当的安全机制的指导，即，在安全性方面，实现应该对报告块应用加密和认证。例如，这可以通过将AVPF配置文件与[RFC3711]中定义的安全RTP配置文件一起使用来实现；[RFC5124]中规定了两个配置文件的适当组合（“SAVPF”）。但是，也存在其他机制（见[RFC7201]），可能更合适。
New block types for RTCP XR are subject to IANA registration. For general guidelines on IANA considerations for RTCP XR, please refer to [RFC3611].
RTCP XR的新块类型需要IANA注册。有关RTCP XR的IANA注意事项的一般指南，请参阅[RFC3611]。
This document assigns the block type value 34 to Video Loss Concealment Metric Report Block in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry".
本文档将块类型值34分配给IANA“RTP控制协议扩展报告（RTCP XR）块类型注册表”中的视频丢失隐藏度量报告块。
This document also registers a new parameter "video-loss-concealment" in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry".
本文档还在“RTP控制协议扩展报告（RTCP XR）会话描述协议（SDP）参数注册表”中注册新参数“视频丢失隐藏”。
The contact information for the registration is:
注册的联系信息为：
RAI Area Directors <rai-ads@ietf.org>
RAI Area Directors <rai-ads@ietf.org>
[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>.
[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, DOI 10.17487/RFC3611, November 2003, <http://www.rfc-editor.org/info/rfc3611>.
[RFC3611]Friedman，T.，Ed.，Caceres，R.，Ed.，和A.Clark，Ed.，“RTP控制协议扩展报告（RTCP XR）”，RFC 3611，DOI 10.17487/RFC36112003年11月<http://www.rfc-editor.org/info/rfc3611>.
[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>.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, <http://www.rfc-editor.org/info/rfc5234>.
[RFC5234]Crocker，D.，Ed.，和P.Overell，“语法规范的扩充BNF:ABNF”，STD 68，RFC 5234，DOI 10.17487/RFC5234，2008年1月<http://www.rfc-editor.org/info/rfc5234>.
[RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information Reporting Using a Source Description (SDES) Item and an RTCP Extended Report (XR) Block", RFC 6776, DOI 10.17487/RFC6776, October 2012, <http://www.rfc-editor.org/info/rfc6776>.
[RFC6776]Clark，A.和Q.Wu，“使用源描述（SDES）项和RTCP扩展报告（XR）块的测量标识和信息报告”，RFC 6776，DOI 10.17487/RFC6776，2012年10月<http://www.rfc-editor.org/info/rfc6776>.
[RFC7294] Clark, A., Zorn, G., Bi, C., and Q. Wu, "RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Concealment Metrics Reporting on Audio Applications", RFC 7294, DOI 10.17487/RFC7294, July 2014, <http://www.rfc-editor.org/info/rfc7294>.
[RFC7294]Clark，A.，Zorn，G.，Bi，C.，和Q.Wu，“用于音频应用上隐藏度量报告的RTP控制协议（RTCP）扩展报告（XR）块”，RFC 7294，DOI 10.17487/RFC7294，2014年7月<http://www.rfc-editor.org/info/rfc7294>.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New Performance Metric Development", BCP 170, RFC 6390, DOI 10.17487/RFC6390, October 2011, <http://www.rfc-editor.org/info/rfc6390>.
[RFC6390]Clark，A.和B.Claise，“考虑新绩效指标开发的指南”，BCP 170，RFC 6390，DOI 10.17487/RFC6390，2011年10月<http://www.rfc-editor.org/info/rfc6390>.
[RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design Considerations for Protocol Extensions", RFC 6709, DOI 10.17487/RFC6709, September 2012, <http://www.rfc-editor.org/info/rfc6709>.
[RFC6709]Carpenter，B.，Aboba，B.，Ed.，和S.Cheshire，“协议扩展的设计考虑”，RFC 6709，DOI 10.17487/RFC6709，2012年9月<http://www.rfc-editor.org/info/rfc6709>.
[RFC6792] Wu, Q., Ed., Hunt, G., and P. Arden, "Guidelines for Use of the RTP Monitoring Framework", RFC 6792, DOI 10.17487/RFC6792, November 2012, <http://www.rfc-editor.org/info/rfc6792>.
[RFC6792]Wu，Q.，Ed.，Hunt，G.，和P.Arden，“RTP监测框架的使用指南”，RFC 6792，DOI 10.17487/RFC6792，2012年11月<http://www.rfc-editor.org/info/rfc6792>.
[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>.
a. Video Impaired Duration Metric
a. 视频受损持续时间度量
* Metric Name: Video Impaired Duration Metric
* 度量名称：视频受损持续时间度量
* Metric Description: The total duration of the video impaired by transmission loss before applying any loss concealment methods.
* 度量说明：在应用任何损失隐藏方法之前，因传输损失而受损的视频的总持续时间。
* Method of Measurement or Calculation: The metric is based on measurements that are typically made at the time that a video frame is decoded and rendered for playout.
* 测量或计算方法：度量基于通常在视频帧解码和渲染以便播放时进行的测量。
* Units of Measurement: This metric is expressed in units of RTP timestamp.
* 度量单位：此度量以RTP时间戳为单位表示。
* Measurement Point(s) with Potential Measurement Domain: It is measured at the receiving end of the RTP stream.
* 具有潜在测量域的测量点：在RTP流的接收端测量。
* Measurement Timing: See paragraph 1 of Section 4.
* 测量时间：见第4节第1段。
* Use and Applications: The metric is applicable to video applications of RTP and the video component of audio/video applications in which packet loss concealment mechanisms are applied to the receiving endpoint to mitigate the impact of network impairments on QoE.
* 用途和应用：该指标适用于RTP的视频应用和音频/视频应用的视频组件，其中分组丢失隐藏机制应用于接收端点，以减轻网络损伤对QoE的影响。
b. Video Concealed Duration Metric
b. 视频隐藏持续时间度量
* Metric Name: Video Concealed Duration Metric
* 度量名称：视频隐藏持续时间度量
* Metric Description: The total duration of concealed damaged video pictures on which loss concealment method corresponding to Video Loss Concealment Method Type is applied.
* 度量说明：应用与视频丢失隐藏方法类型对应的丢失隐藏方法的隐藏损坏视频图片的总持续时间。
* Method of Measurement or Calculation: The metric is based on measurements that are typically made at the time that a video frame is decoded and rendered for playout.
* 测量或计算方法：度量基于通常在视频帧解码和渲染以便播放时进行的测量。
* Units of Measurement: This metric is expressed in units of RTP timestamp.
* 度量单位：此度量以RTP时间戳为单位表示。
* Measurement Point(s) with Potential Measurement Domain: It is measured at the receiving end of the RTP stream.
* 具有潜在测量域的测量点：在RTP流的接收端测量。
* Measurement Timing: See paragraph 1 of Section 4.
* 测量时间：见第4节第1段。
* Use and Applications: These metrics are applicable to video applications of RTP and the video component of audio/video applications in which packet loss concealment mechanisms are incorporated into the receiving endpoint to mitigate the impact of network impairments on QoE.
* 用途和应用：这些指标适用于RTP的视频应用和音频/视频应用的视频组件，其中分组丢失隐藏机制被合并到接收端点以减轻网络损伤对QoE的影响。
c. Mean Video Frame-Freeze Duration Metric
c. 平均视频帧冻结持续时间度量
* Metric Name: Mean Video Frame-Freeze Duration Metric
* 度量名称：平均视频帧冻结持续时间度量
* Metric Description: The mean duration of the frame-freeze events.
* 度量说明：帧冻结事件的平均持续时间。
* Method of Measurement or Calculation: The metric is based on measurements that are typically made at the time that a video frame is decoded and rendered for playout. The metric is calculated by summing the total duration of all frame-freeze events and dividing by the number of events.
* 测量或计算方法：度量基于通常在视频帧解码和渲染以便播放时进行的测量。通过将所有帧冻结事件的总持续时间相加并除以事件数来计算度量。
* Units of Measurement: This metric is expressed in units of RTP timestamp.
* 度量单位：此度量以RTP时间戳为单位表示。
* Measurement Point(s) with Potential Measurement Domain: It is measured at the receiving end of the RTP stream.
* 具有潜在测量域的测量点：在RTP流的接收端测量。
* Measurement Timing: See paragraph 1 of Section 4.
* 测量时间：见第4节第1段。
* Use and Applications: These metrics are applicable to video applications of RTP and the video component of audio/video applications in which packet loss concealment mechanisms are incorporated into the receiving endpoint to mitigate the impact of network impairments on QoE.
* 用途和应用：这些指标适用于RTP的视频应用和音频/视频应用的视频组件，其中分组丢失隐藏机制被合并到接收端点以减轻网络损伤对QoE的影响。
d. Mean Impaired Video Frame Proportion Metric
d. 平均受损视频帧比例度量
* Metric Name: Mean Impaired Video Frame Proportion Metric
* 指标名称：平均受损视频帧比例指标
* Metric Description: Mean proportion of each video frame impaired by loss before applying any loss concealment method during the interval.
* 度量说明：在间隔期间应用任何丢失隐藏方法之前，因丢失而受损的每个视频帧的平均比例。
* Method of Measurement or Calculation: The metric is based on measurements that are typically made at the time that a video frame is decoded and rendered for playout. It is calculated by summing the impaired proportion of each video frame and dividing by the number of frames during this period. The impaired proportion of each video frame is obtained by dividing the number of missing macroblocks from this video frame by the
* 测量或计算方法：度量基于通常在视频帧解码和渲染以便播放时进行的测量。计算方法是将每个视频帧的受损比例相加，然后除以该期间的帧数。每个视频帧的受损比例通过将该视频帧中缺失宏块的数量除以
total macroblock number of the video frame, which is equivalent to multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.
视频帧的总宏块数，相当于将除法结果乘以256，将最大值限制为255（以避免溢出），并取整数部分。
* Units of Measurement: This metric is expressed as a fixed-point number with the binary point at the left edge of the field.
* 度量单位：此度量单位表示为一个定点数字，二进制点位于字段的左边缘。
* Measurement Point(s) with Potential Measurement Domain: It is measured at the receiving end of the RTP stream.
* 具有潜在测量域的测量点：在RTP流的接收端测量。
* Measurement Timing: See paragraph 1 of Section 4.
* 测量时间：见第4节第1段。
* Use and Applications: These metrics are applicable to video applications of RTP and the video component of audio/video applications in which packet loss concealment mechanisms are incorporated into the receiving endpoint to mitigate the impact of network impairments on QoE.
* 用途和应用：这些指标适用于RTP的视频应用和音频/视频应用的视频组件，其中分组丢失隐藏机制被合并到接收端点以减轻网络损伤对QoE的影响。
e. Mean Concealed Video Frame Proportion Metric
e. 平均隐藏视频帧比例度量
* Metric Name: Mean Concealed Video Frame Proportion Metric
* 指标名称：平均隐藏视频帧比例指标
* Metric Description: Mean proportion of each video frame to which loss concealment (using Video Loss Concealment Method Type) was applied during the interval.
* 度量说明：间隔期间应用丢失隐藏（使用视频丢失隐藏方法类型）的每个视频帧的平均比例。
* Method of Measurement or Calculation: The metric is based on measurements that are typically made at the time that a video frame is decoded and rendered for playout. It is calculated by summing the concealed proportion of each video frame and dividing by the number of frames during this period. The concealed proportion of each video frame is obtained by dividing the number of concealed macroblocks from this video frame by the total macroblock number of the video frame, which is equivalent to multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.
* 测量或计算方法：度量基于通常在视频帧解码和渲染以便播放时进行的测量。计算方法是将每个视频帧的隐藏比例相加，然后除以该期间的帧数。每个视频帧的隐藏比例是通过将来自该视频帧的隐藏宏块的数量除以视频帧的总宏块数量来获得的，这相当于将分割结果乘以256，将最大值限制为255（以避免溢出），并取整数部分。
* Units of Measurement: This metric is expressed as a fixed-point number with the binary point at the left edge of the field.
* 度量单位：此度量单位表示为一个定点数字，二进制点位于字段的左边缘。
* Measurement Point(s) with Potential Measurement Domain: It is measured at the receiving end of the RTP stream.
* 具有潜在测量域的测量点：在RTP流的接收端测量。
* Measurement Timing: See paragraph 1 of Section 4.
* 测量时间：见第4节第1段。
* Use and Applications: These metrics are applicable to video applications of RTP and the video component of audio/video applications in which packet loss concealment mechanisms are incorporated into the receiving endpoint to mitigate the impact of network impairments on QoE.
* 用途和应用：这些指标适用于RTP的视频应用和音频/视频应用的视频组件，其中分组丢失隐藏机制被合并到接收端点以减轻网络损伤对QoE的影响。
f. Fraction of Video Frames Subject to Concealment Metric
f. 受隐藏度量约束的视频帧的分数
* Metric Name: Fraction of Video Frames Subject to Concealment Metric
* 度量名称：受隐藏度量约束的视频帧的分数
* Metric Description: Proportion of concealed video frames to which loss concealment (using the Video Loss Concealment Method Type) was applied compared to the total number of frames during the interval.
* 度量说明：应用丢失隐藏（使用视频丢失隐藏方法类型）的隐藏视频帧与间隔期间的总帧数的比例。
* Method of Measurement or Calculation: The metric is based on measurements that are typically made at the time that a video frame is decoded and rendered for playout. This metric is calculated by dividing the number of frames to which loss concealment (using Video Loss Concealment Method Type) was applied by the total number of frames. It is equivalent to multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.
* 测量或计算方法：度量基于通常在视频帧解码和渲染以便播放时进行的测量。通过将应用丢失隐藏（使用视频丢失隐藏方法类型）的帧数除以总帧数来计算此度量。这相当于将除法的结果乘以256，将最大值限制为255（以避免溢出），并取整数部分。
* Units of Measurement: This metric is expressed as a fixed-point number with the binary point at the left edge of the field.
* 度量单位：此度量单位表示为一个定点数字，二进制点位于字段的左边缘。
* Measurement Point(s) with Potential Measurement Domain: It is measured at the receiving end of the RTP stream.
* 具有潜在测量域的测量点：在RTP流的接收端测量。
* Measurement Timing: See paragraph 1 of Section 4.
* 测量时间：见第4节第1段。
* Use and Applications: These metrics are applicable to video applications of RTP and the video component of audio/video applications in which packet loss concealment mechanisms are incorporated into the receiving endpoint to mitigate the impact of network impairments on QoE.
* 用途和应用：这些指标适用于RTP的视频应用和音频/视频应用的视频组件，其中分组丢失隐藏机制被合并到接收端点以减轻网络损伤对QoE的影响。
Acknowledgements
致谢
The author would like to thank Colin Perkins and Roni Even for their valuable comments.
作者要感谢科林·帕金斯和罗尼，即使他们提出了宝贵的意见。
Authors' Addresses
作者地址
Rachel Huang Huawei 101 Software Avenue, Yuhua District Nanjing 210012 China
中国南京市雨花区华为软件大道101号，邮编：210012
Email: rachel.huang@huawei.com
Email: rachel.huang@huawei.com