1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T J.189TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Corrigendum 1(04/2003) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Miscellaneous Seamless splicing for MPEG-2 bit streams Corrigendum 1 ITU-T Re
2、commendation J.189 (2002) Corrigendum 1 ITU-T J-SERIES RECOMMENDATIONS CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS General Recommendations J.1J.9 General specifications for analogue sound-programme transmission J.10J.19 Performance characteristics of a
3、nalogue sound-programme circuits J.20J.29 Equipment and lines used for analogue sound-programme circuits J.30J.39 Digital encoders for analogue sound-programme signals J.40J.49 Digital transmission of sound-programme signals J.50J.59 Circuits for analogue television transmission J.60J.69 Analogue te
4、levision transmission over metallic lines and interconnection with radio-relay links J.70J.79 Digital transmission of television signals J.80J.89 Ancillary digital services for television transmission J.90J.99 Operational requirements and methods for television transmission J.100J.109 Interactive sy
5、stems for digital television distribution J.110J.129 Transport of MPEG-2 signals on packetised networks J.130J.139 Measurement of the quality of service J.140J.149 Digital television distribution through local subscriber networks J.150J.159 IPCablecom J.160J.179 Miscellaneous J.180J.199 Application
6、for Interactive Digital Television J.200J.209 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. J.189 (2002)/Cor.1 (04/2003) i ITU-T Recommendation J.189 Seamless splicing for MPEG-2 bit streams Corrigendum 1 Source Corrigendum 1 to ITU-T Recommendation J.189 was app
7、roved by ITU-T Study Group 9 (2001-2004) under the WTSA Resolution 1 on 4 April 2003. ii ITU-T Rec. J.189 (2002)/Cor.1 (04/2003) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardiza
8、tion 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 Standardization Assembly (WTSA), which me
9、ets 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 technology which fall within ITU-Ts
10、 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. Compliance with this Recommendation is
11、 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 obligatory language such as “must“ a
12、nd 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 implementation of this Recommendation may in
13、volve 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 the date of approval of this Re
14、commendation, 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 consult the TSB patent database. IT
15、U 2003 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. J.189 (2002)/Cor.1 (04/2003) iii CONTENTS Page 1) Clause 1 Scope. 1 2) Clause 4.2 MPEG-2 bit-stream syntax required for seamless splicing . 2 3)
16、 Clause 4.3.1 Basic mechanism based on ITU-T Rec. J.181 2 4) Clause 4.3.2 Constraints for seamless splicing 3 5) Clause 4.3.2.1.2 For video or audio PID streams 3 6) Clause 4.3.2.2.2 For video or audio PID streams 4 ITU-T Rec. J.189 (2002)/Cor.1 (04/2003) 1 ITU-T Recommendation J.189 Seamless splici
17、ng for MPEG-2 bit streams Corrigendum 1 1) Clause 1 Scope Modify this clause as follows: The processing of the MPEG-2 bit stream is becoming increasingly necessary in television transmission chains to avoid picture quality degradation due to multiple cascaded MPEG-2 encoding and decoding cycles. In
18、fact, Many local television operators normally receive several TV programtelevision signals from different or remote sources in the form of MPEG-2 bit streams. They switch these program signals at an appointed time to produce complete TV television programs signals, or they insert local advertisemen
19、ts and emergency messages into already complete television programsthe TV program signals. In these switching systems, seamless bit-stream insertions, splicing has been strongly demandedrequired to avoid picture quality degradation on the splicing point at the decoder side. For MPEG-2 bit-stream spl
20、icing, two a number of techniques have been recommended, including those in ITU-T Recs H.222.0 | ISO/IEC 13818-1 and J.181. An MPEG-2 syntax of a spliceable bit stream recommended in ITU-T Rec. H.222.0 | ISO/IEC 13818-1 means a PID stream whose discontinuity in a time-stamp or a time base can be pro
21、cessed seamlessly by the MPEG-2 bit stream splicing device. These syntaxes are defined as splicing point flag, seamless splice flag, splice type and so forth. The transport mechanism of scheduling information on a splicing event for splicing devices is also recommended in ITU-T Rec. J.181. This Reco
22、mmendation specifies a seamless splicing technique for the MPEG-2 bit stream based on the two existing Recommendations above. The MPEG-2 syntax of a spliceable bit stream is fully in accordance with ITU-T Rec. H.222.0 | ISO/IEC 13818-1, while the transport mechanism of scheduling information is modi
23、fied by applying some constraints on the streams being spliced. “Seamless splicing“, as used here, means switching from one MPEG-2 video elementary stream to a second video elementary stream supplied to a single decoderin such manner that: cContinuity of the spliced bit stream is maintained; Switchi
24、ng occurs at a Transport Stream packet boundary; nNo underflow or overflow of the decoder buffer occurs as a result of the splice; Correct bitstream syntax as defined in ITU-T Rec. H.222.0 is maintained and the splice may result in discontinuities in timebase or continuity counter; nNo visible artif
25、acts in the reconstructed baseband video are introduced. The syntax of a spliceable bitstream recommended in ITU-T Rec. H.222.0 means that a PID stream whose discontinuity in a time stamp or a time base can be processed seamlessly by an MPEG-2 T-STD decoder. The syntax elements to be used are the sp
26、licing point flag, seamless splice flag, splice type, and so forth. This method places constraints on the two bit streams that may be limiting in actual use. The reader is directed to Annex K/H.222.0. This current Recommendation specifies a seamless splicing technique for the MPEG-2 bit stream based
27、 on the two existing Recommendations above. The resulting MPEG-2 syntax of a spliced bit stream is fully in accordance with ITU-T Rec. H.222.0. The splicing signalling information is based on ITU-T Rec. J.181. The bit stream requirements of ITU-T Rec. J.181 are modified, 2 ITU-T Rec. J.189 (2002)/Co
28、r.1 (04/2003) applying the constraints of SMPTE 312M and additional program splice constraints on the streams being spliced. In addition, other types of splicing schemes without any splicing informationbit stream constraints are given in the appendices as reference information. 2) Clause 4.2 MPEG-2
29、bit-stream syntax required for seamless splicing Modify the text in this clause as follows: Those basic fields constituting a spliceable bit stream are defined as splicing_point_flag, splice_countdown, seamless_splice_flag, splice_type and DTS_next_AU in ITU-T Rec. H.222.0 | ISO/IEC 13818-1. These f
30、ields are mapped into an adaptation field of transport stream packets as shown in Figure 2, and the definition of each field is summarized thereafter. splicing_point_flag: When set to “1“, this field indicates the presence of the splice_countdown field, specifying the occurrence of a splicing point.
31、 splice_countdown: A positive value specifies the remaining number of transport stream packets, of the same PID, following the associated transport stream packet until a splice point is reached. The transport stream packet in which the splice_countdown field reaches zero corresponds to the Out Point
32、 packet. A negative value specifies that the associated transport stream packet is the packet following the splicing point. seamless_splice_flag: When set to “1“, it indicates the presence of the splice_type and DTS_next_AU fields. splice_type: This field indicates the condition that shall be respec
33、ted by an associated elementary stream for splicing purposes especially for video PID streams. DTS_next_AU: This field indicates the decoding time of the first access unit following the splicing point, where the decoding time is expressed in the time base, which is valid in the transport stream pack
34、et in which the splice_countdown reaches zero. When the bit stream is assumed to be a spliceable one as described above, seamless splicing is basically enabled based on simple bit-stream switching as shown in Figure 3, when using an appropriate splicinger equipment. Simple Bbit-stream splicing is ap
35、plied directly to bit streams where possible splice points must be provided by the upstream encoder. In addition, the upstream encoder must control the number of encoded bits to put the downstream decoder in a stable buffer state at each Out Point, otherwise simple seamless switching can not be real
36、ized. The splicing device based on this approach can be implemented without any re-encoding processing. Other splicing approaches which do not require any constraints on bit-stream splice points exist. Two such approaches are described in the appendices. 3) Clause 4.3.1 Basic mechanism based on ITU-
37、T Rec. J.181 Modify this clause as follows: Detailed information on a splicing event (the possible splice point, the PID of the spliced stream, the schedule of upcoming splicing events, etc.) can be mapped into a bit stream as the splice information section specified in ITU-T Rec. J.181. The splice
38、information section notifies the splicing device of scheduled splice events prior to the arrival of splice points, and enables the splicing device to ensure a reliable splicing operation. The splice information section shall be carried in transport stream packets within their own PID streams. ITU-T
39、Rec. J.181 itself makes no requirements for the preconditioning of an input MPEG stream in addition to the MPEG-2 standards and it also places no requirements upon how a splicing device must operate. ITU-T Rec. J.181 is limited entirely to the area of signalling. Table 1 shows the syntax of the spli
40、ce information section.See ITU-T Rec. J.181 for details. ITU-T Rec. J.189 (2002)/Cor.1 (04/2003) 3 Table 1/J.189 Syntax of the splice information section defined in ITU-T Rec. J.181 Syntax Bits Mnemonic Encrypted splice_info_section () table_id section_syntax_indicator private_indicator reserved sec
41、tion_length protocol_version encrypted_packet encryption_algorithm pts_adjustment cw_index reserved splice_command_type if (splice_command_type=0x00) splice_null () if (splice_command_type=0x04) splice_schedule () if (splice_command_type=0x05) splice_insert () descriptor_loop_length for ( I=0; IN; I
42、+ ) splice_descriptor () for ( I=0; IN; I+ ) alignment_stuffing if (encrypted_packet) E_CRC_32 CRC_32 8 1 1 2 12 8 1 6 33 8 24 8 16 8 32 32 uimsbf bslbf bslbf bslbf uimsbf uimsbf bslbf uimsbf uimsbf uimsbf bslbf uimsbf uimsbf bslbf rpchof rpchof E E E E E E E E 4) Clause 4.3.2 Constraints for seamle
43、ss splicing Modify this clause as follows: When applying ITU-T Rec. J.181 as the splice information section, ITU-T Rec. J.189 requires that the Out Point and the In Point shall meet the following constraints in order to achieve seamless splicing. For video PID streams, seamless splicing between a lo
44、w-delay sequence and a sequence containing at least one B-picture is not aimed at in this Recommendation. 5) Clause 4.3.2.1.2 For video or audio PID streams Modify this clause as follows: The seamless_splice_flag shall be set to 1 in the Out Point packet. DTS_next_AU shall be set in the Out Point pa
45、cket, according to the definition in ITU-T Rec. H.222.0 | ISO/IEC 13818-1. 4 ITU-T Rec. J.189 (2002)/Cor.1 (04/2003) The Out Point packet shall carry the splice_type field. For video PID streams, the value of the splice_type shall be selected from the table defined in ITU-T Rec. H.222.0 | ISO/IEC 13
46、818-1. For audio PID streams, the value of the splice_type shall be set to “0000“. For video PID streams, the last picture (in presentation order) preceding an Out Point shall be either a P- or an I-picture. An Out Point shall not occur between the two fields of a coded frame. To enable seamless spl
47、icing, the last payload byte of the Out Point Packet shall remain in the VBV buffer an amount of time equal to: splice_decoding_delay Display_Period_last_AUold; where Display_Period_last_AUoldis the display duration of the video access unit of the old material which begins presentation at the time w
48、hen the last video access unit is removed from the buffer (see ITU-T Rec. H.222.0 (2000) | ISO/IEC 13818-1:2000). To enable seamless splicing, the last picture (in presentation order) before an Out Point shall be either a frame picture or a bottom field picture. In the case of an interlaced sequence
49、 (progressive_sequence equals 0), the following constraints on the use of top_field_first and repeat_first_field shall apply: If the last picture (in presentation order) before an Out Point is a frame picture with the top_field_first bit equal to 1, then the repeat_first_field bit of that picture shall be 0. If the last picture (in presentation order) before an Out Point is a frame picture with the top_field_first bit equal to 0, then the repeat_first_field bit of that picture shall be 1. For audio PID streams
