1、 International Telecommunication Union ITU-T H.271TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2006) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Coding of moving video Video back-channel messages for conveyance of status information and requests from a v
2、ideo receiver to a video sender ITU-T Recommendation H.271 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE OF AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Syste
3、ms aspects H.230H.239 Communication procedures H.240H.259 Coding of moving video H.260H.279 Related systems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service arch
4、itecture for audiovisual and multimedia services H.360H.369 Supplementary services for multimedia H.450H.499 MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519
5、 Mobile multimedia collaboration applications and services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559Mobile multimedia collaboration inter-work
6、ing procedures H.560H.569 BROADBAND AND TRIPLE-PLAY MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. H.271 (05/2006) i ITU-T Recommendation H.271 Video back-channel messages for conveyance of sta
7、tus information and requests from a video receiver to a video sender Summary This Recommendation specifies the format of back-channel messages for conveyance of status information and requests from a video receiver to a video sender. The message syntax has been designed in a generic way to make it a
8、pplicable for use with the majority of the existing international video coding standards. The application of the generic messages to ITU-T Recs H.261, H.263, and H.264 | ISO/IEC 14496-10 is specified. Source ITU-T Recommendation H.271 was approved on 29 May 2006 by ITU-T Study Group 16 (2005-2008) u
9、nder the ITU-T Recommendation A.8 procedure. Keywords Back-channel message, receiver feedback, reference picture selection, video. ii ITU-T Rec. H.271 (05/2006) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The I
10、TU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardi
11、zation Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information tec
12、hnology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compli
13、ance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other oblig
14、atory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementatio
15、n of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of
16、the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to cons
17、ult the TSB patent database. ITU 2006 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. H.271 (05/2006) iii CONTENTS Page 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Abbreviations 2 5 Conventi
18、ons 2 5.1 Arithmetic operators. 2 5.2 Logical operators 3 5.3 Relational operators 3 5.4 Bit-wise operators. 3 5.5 Assignment operators . 3 5.6 Variables, syntax elements, and tables. 4 5.7 Text description of logical operations 4 5.8 Method of describing syntax in tabular form . 5 5.9 Specification
19、 of syntax functions, categories, and descriptors. 7 6 Message payloads . 8 6.1 Syntax. 8 6.2 Semantics 9 7 Standard specific uses of the messages 11 7.1 H.261 specific use of the messages 11 7.2 H.263 specific use of the messages 12 7.3 H.264 specific use of the messages 13 iv ITU-T Rec. H.271 (05/
20、2006) Introduction 0.1 Purpose For some applications, the transmission of additional data (in-band or out-of-band) is useful for improving video quality of service. This Recommendation specifies data payloads for use with a variety of video coding technologies. The data payloads are specified in a g
21、eneric way to make them applicable to prevalent existing video coding standards. The application of the generic messages to ITU-T Recs H.261, H.263, and H.264 is specified. 0.2 Overview The following information can be signalled from a video receiver to a video sender using the back-channel message(
22、s) defined in this Recommendation: Status reports: One or more pictures that are without detected bitstream error mismatch; Picture-level and/or macroblock-level losses; Information of important header information. Update requests: A “reset“ request indicating that the sender should completely refre
23、sh the video bitstream as if no prior bitstream data had been received. The application of the back-channel messages to ITU-T Recs H.261, H.263, and H.264 is specified. ITU-T Rec. H.271 (05/2006) 1 ITU-T Recommendation H.271 Video back-channel messages for conveyance of status information and reques
24、ts from a video receiver to a video sender 1 Scope This Recommendation specifies back-channel messages for block-based video coding. 2 Normative references The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this
25、 Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other
26、references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T Recommendation H.261 (1993), Video codec for audiovisual serv
27、ices at p 64 kbit/s. ITU-T Recommendation H.263 (2005), Video coding for low bit rate communication. ITU-T Recommendation H.264 (2005), Advanced video coding for generic audiovisual services. ISO/IEC 14496-10:2005, Information technology Coding of audio-visual objects Part 10: Advanced Video Coding.
28、 3 Definitions This Recommendation defines the following terms: 3.1 back channel: A means to convey back-channel messages from a receiver of a video bitstream to a sender of a video bitstream. 3.2 back-channel message: A message that is generated by a receiver of a video bitstream that conveys recei
29、ver status information or requests. 3.3 bitstream: A sequence of bits that forms the representation of coded pictures and associated data forming one or more coded video sequences. 3.4 bitstream error: A corrupted or incomplete bitstream. 3.5 bitstream error mismatch: A difference between the values
30、 or quantity of decoded pictures caused by one or more bitstream errors versus the values or quantity of decoded pictures generated by the decoding process with a bitstream without bitstream errors. 3.6 block: An MxN (M-column by N-row) array of luma samples and the associated chroma samples. 3.7 de
31、tected bitstream error: A bitstream error that is detected by the receiver. 3.8 detected bitstream error mismatch: A bitstream error mismatch that may be present because of bitstream errors. 3.9 decoding order: The order in which syntax elements are processed by the decoding process specified by a v
32、ideo coding technology. 2 ITU-T Rec. H.271 (05/2006) 3.10 macroblock: A 16x16 block of luma samples and two corresponding blocks of chroma samples. 3.11 parameter set: A syntax structure that contains a number of syntax elements that may be used in the decoding process for one or more pictures. 3.12
33、 picture: A collective term for a field or a frame of video that is coded as a distinct unit by a video coding technology. 3.13 reference picture: A picture that contains samples that may be used for inter-picture prediction in the decoding process of subsequent pictures in the video bitstream. 3.14
34、 reserved: The term reserved, when used in the clauses specifying some values of a particular syntax element, are for future use by ITU-T. These values shall not be used in back-channel messages conforming to this Recommendation, but may be used in future extensions of this Recommendation by ITU-T.
35、3.15 syntax element: An element of data represented in the bitstream or in a back-channel message. 4 Abbreviations This Recommendation uses the following abbreviations: CRC Cyclic Redundancy Code LSB Least Significant Bit MSB Most Significant Bit 5 Conventions Throughout this Recommendation, stateme
36、nts appearing with the preamble “NOTE “ are informative and are not an integral part of this Recommendation. NOTE The mathematical operators used in this Recommendation are similar to those used in the C programming language. Numbering and counting conventions generally begin from 0. 5.1 Arithmetic
37、operators The following arithmetic operators are defined as follows. + Addition Subtraction (as a two-argument operator) or negation (as a unary prefix operator) * Multiplication / Integer division with truncation of the result toward zero. For example, 7/4 and (7) / (4) are truncated to 1 and (7) /
38、 4 and 7 / (4) are truncated to 1. x % y Modulus. Remainder of x divided by y, defined only for integers x and y with x 0 and y 0. When order of precedence is not indicated explicitly by use of parenthesis, the following rules apply: multiplication and division operations are considered to take plac
39、e before addition and subtraction; multiplication and division operations in sequence are evaluated sequentially from left to right; addition and subtraction operations in sequence are evaluated sequentially from left to right. ITU-T Rec. H.271 (05/2006) 3 5.2 Logical operators The following logical
40、 operators are defined as follows: x otherwise, evaluates to the value of z 5.3 Relational operators The following relational operators are defined as follows: Greater than = Greater than or equal to y Arithmetic right shift of a twos complement integer representation of x by y binary digits. This f
41、unction is defined only for positive integer values of y. Bits shifted into the MSBs as a result of the right shift have a value equal to the MSB of x prior to the shift operation. x 5 Reserved for future use by ITU-T Messages having payloadType greater than 5 shall be removed and discarded accordin
42、g to the size of the message as indicated by payloadSize. ref_pic_id identifies a picture. Depending on the value of payloadType, the semantics of ref_pic_id are as specified in Table 6-2. 10 ITU-T Rec. H.271 (05/2006) Table 6-2/H.271 Semantics of ref_pic_id payloadType Semantics of ref_pic_id 0 Spe
43、cifies a picture without detected bitstream error mismatch. 1 Specifies a picture that has been entirely or partially lost. 2 Specifies a picture that has been partially lost. 3 Specifies a picture. A CRC is present for one parameter set associated with the specified picture. 4 Specifies a picture.
44、One CRC is present for all parameter sets of a certain type that are stored at the time associated with the decoding of the specified picture. num_ref_pics_minus1 plus 1 specifies the number of the pictures that are without detected bitstream error mismatch. The value of num_ref_pics_minus1 shall be
45、 in the range of 0 to 31, inclusive. good_ref_pic_id i specifies the ithpicture indicated in the current message that is without detected bitstream error mismatch. delta_ref_pic_id specifies an increment relative to ref_pic_id identifying a set of pictures that are entirely or partially lost. The va
46、lue of delta_ref_pic_id shall be in the range of 0 to 31, inclusive. data_partition_idc indicates that all data (when data_partition_idc is equal to 0) or a partition of the data (when data_partition_idc is not equal to 0) for the blocks specified by top_left_blk and bottom_right_blk is lost. The va
47、lue of data_partition_idc shall be in the range of 0 to 15, inclusive. run_length_flag equal to 1 indicates the presence of the syntax elements first_blk_lost and num_blks_lost_minus1. run_length_flag equal to 0 indicates the presence of the syntax elements top_left_blk and bottom_right_blk. first_b
48、lk_lost indicates the block address of the first block in raster scan order. A block address is the index of a block in a block raster scan of the picture starting with zero for the top-left block in a picture. num_blks_lost_minus1 plus 1 specifies the number of consecutive blocks in raster scan ord
49、er with the first block being identified by first_blk_lost. top_left_blk and bottom_right_blk specify the block addresses of the top-left and bottom-right blocks, respectively, of the rectangular region that is entirely or partially lost. The following constraints shall be obeyed by the values of the syntax elements top_left_blk and bottom_right_blk, where the variable PicWidthInBlks is the picture width in units of blocks. top_left_blk shall be less than or equal to bottom_right_blk. bottom_right_blk shall be less th
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