1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T J.189TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2002) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Miscellaneous Seamless splicing for MPEG-2 bit streams ITU-T Recommendation J.189 ITU-T J-
2、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 analogue sound-programme circuits J.20J.29 Equipm
3、ent 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 television transmission over metallic lines and in
4、terconnection 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 systems for digital television distribution J.110J
5、.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 for Interactive Digital Television J.200J.209 Fo
6、r further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. J.189 (07/2002) i ITU-T Recommendation J.189 Seamless splicing for MPEG-2 bit streams Summary This Recommendation specifies an MPEG-2 bit-stream syntax for transport stream splicing and a transport mechanism of scheduli
7、ng information for splicing devices to enable seamless splicing for digital program insertion, which means that different program signals are switched at an appointed time to produce complete TV programs or to insert local advertisements and emergency messages into the TV program signals. Source ITU
8、-T Recommendation J.189 was prepared by ITU-T Study Group 9 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 July 2002. ii ITU-T Rec. J.189 (07/2002) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunicatio
9、ns. The ITU 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
10、Standardization 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 inform
11、ation technology 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 agenc
12、y. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation 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 Ri
13、ghts, whether asserted by ITU members or others outside of the Recommendation development process. As of 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
14、are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2002 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 (0
15、7/2002) iii CONTENTS Page 1 Scope 1 2 References. 1 2.1 Normative references 1 2.2 Informative references 2 3 Terms, definitions and acronyms 2 4 MPEG-2 bit-stream insertion techniques 2 4.1 Configuration 2 4.2 MPEG-2 bit-stream syntax required for seamless splicing 3 4.3 Transport mechanism of sche
16、duling information for splicing devices 4 4.3.1 Basic mechanism based on ITU-T Rec. J.181 4 4.3.2 Constraints for seamless splicing . 5 Appendix I Re-encoding with the side information approach 7 Appendix II Partial re-encoding approach 8 ITU-T Rec. J.189 (07/2002) 1 ITU-T Recommendation J.189 Seaml
17、ess splicing for MPEG-2 bit streams 1 Scope The processing of the MPEG-2 bit stream is becoming increasingly necessary in a TV transmission chain to avoid picture quality degradation due to multiple cascaded MPEG-2 encoding and decoding. In fact, local television operators normally receive several T
18、V program 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 program signals, or they insert local advertisements and emergency messages into the TV program signals. In these switching, seamless bi
19、t-stream insertions, splicing has been strongly demanded to avoid picture quality degradation on the splicing point at the decoder side. For MPEG-2 bit-stream splicing, two techniques have been recommended in ITU-T Recs H.222.0 | ISO/IEC 13818-1 and J.181. An MPEG-2 syntax of a spliceable bit stream
20、 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 processed 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 tran
21、sport mechanism of scheduling information on a splicing event for splicing devices is also recommended in ITU-T Rec. J.181. This Recommendation 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 str
22、eam is fully in accordance with ITU-T Rec. H.222.0 | ISO/IEC 13818-1, while the transport mechanism of scheduling information is modified by applying some constraints on the streams being spliced. “Seamless splicing“ here means switching from one MPEG-2 video elementary stream to a second elementary
23、 stream supplied to a single decoder such that: continuity of the spliced bit stream is maintained; no underflow or overflow of the decoder buffer occurs as a result of the splice; no visible artifacts in the reconstructed baseband video are introduced. In addition, other types of splicing schemes w
24、ithout any splicing information are given in the appendices as reference information. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions
25、 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 references listed below. A list of the currently valid IT
26、U-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. 2.1 Normative references ITU-T Recommendation H.222.0 (2000) | ISO/IEC 13818-1:2000, Information technology Generic coding o
27、f moving pictures and associated audio information: Systems. ITU-T Recommendation H.262 (2000) | ISO/IEC 13818-2:2000, Information technology Generic coding of moving pictures and associated audio information: Video. ITU-T Recommendation J.181 (2001), Digital program insertion cueing message for cab
28、le television systems. 2 ITU-T Rec. J.189 (07/2002) 2.2 Informative references SMPTE 312M-2001, Television Splice Points for MPEG-2 Transport Streams. 3 Terms, definitions and acronyms This Recommendation defines the following terms: 3.1 access unit: The coded representation of a video or an audio f
29、rame (see ITU-T Rec. H.262 | ISO/IEC 13818-2). 3.2 bit stream: MPEG-2 transport stream defined in ITU-T Rec. H.222.0 | ISO/IEC 13818-1. 3.3 in point: A point in the bit stream, suitable for entry, that lies on an elementary access unit boundary. 3.4 in point packet: A transport stream packet which c
30、orresponds to the first packet following the In Point. 3.5 out point: A point in the bit stream, suitable for exit, that lies on an elementary access unit boundary. 3.6 out point packet: A transport stream packet which corresponds to the last packet prior to the Out Point. 3.7 PID stream: All the pa
31、ckets with the same PID within a transport stream. 3.8 presentation time-stamp (PTS): A field that may be present in a PES packet header that indicates the time that a presentation unit is presented in the system target decoder. 3.9 presentation unit (PU): A decoded audio access unit or a decoded pi
32、cture (see ITU-T Rec. H.262 | ISO/IEC 13818-2). 3.10 program in point: A group of PID stream In Points that correspond in presentation time. 3.11 program out point: A group of PID stream Out Points that correspond in presentation time. 3.12 program splice point: A Program In Point or a Program Out P
33、oint. 3.13 splice point: A point in a PID stream that is either an Out Point or an In Point. 3.14 spliceable stream: A PID stream whose discontinuity in a time-stamp or a time base can be processed seamlessly by the MPEG-2 bit stream splicing device. The basic syntax is defined in ITU-T Rec. H.222.0
34、 | ISO/IEC 13818-1. 3.15 splice time: A presentation time of the intended splice point, which is equivalent to the presentation time of the access unit following the intended splice point. 4 MPEG-2 bit-stream insertion techniques 4.1 Configuration The basic syntax of a spliceable bit stream is recom
35、mended in ITU-T Rec. H.222.0 | ISO/IEC 13818-1. A spliceable bit stream means a PID stream whose discontinuity in a time-stamp or a time base can be processed seamlessly by the MPEG-2 bit stream splicing device. This mechanism is not sufficient for achieving a reliable splicing operation because of
36、the following reasons: Splicing devices cannot obtain any preceding information indicating the time schedule with regard to upcoming splice points where a seamless program insertion is ensured. ITU-T Rec. J.189 (07/2002) 3 In the case of a program insertion, synchronization of all PID streams, which
37、 constitute the program, cannot necessarily be established. Figure 1 shows the configuration of the splicing technique for the MPEG-2 bit stream assumed in this Recommendation. The transport mechanism of scheduling information is based on ITU-T Rec. J.181 with additional constraints required for the
38、 seamless splicing. This Recommendation defines additional constraints on bit-stream splice points for ITU-T Rec. J.181 and the desirable operation of the splicing device, which are required to achieve the seamless splicing. J.189F01ENCATS (spliceable)Splicing deviceTS (spliceable)TS (spliceable)Sch
39、eduling(J.181)ENCBFigure 1/J.189 Configuration of seamless splicing technique for the MPEG-2 bit stream 4.2 MPEG-2 bit-stream syntax required for seamless splicing Those basic fields constituting a spliceable bit stream are defined as splicing_point_flag, splice_countdown, seamless_splice_flag, spli
40、ce_type and DTS_next_AU in ITU-T Rec. H.222.0 | ISO/IEC 13818-1. These fields are mapped into an adaptation field of transport stream packets as shown in Figure 2, and the definition of each field is summarized thereafter. J.189F025 flagsOPCR3 flagsPCR811 1Splice point flag42 42 8 8 8DTS_next_au1152
41、2 4 3AdaptationfieldlengthDiscontinuityindicatorRandomaccessindicatorElementarystreampriorityindicatorOptionalfieldsStuffingbytesSplicecountdownTransportprivatedatalengthTransportprivatedataAdaptationfieldextensionlengthOptionalfieldsltw_validflagltwoffsetPiece-wiserateSplicetypeSeamless splice flag
42、Figure 2/J.189 Syntax of the adaptation field in the MPEG-2 transport stream packet 4 ITU-T Rec. J.189 (07/2002) splicing_point_flag: When set to “1“, this field indicates the presence of the splice_countdown field, specifying the occurrence of a splicing point. splice_countdown: A positive value sp
43、ecifies 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 packet. A negative value specifies th
44、at 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 respected by an associated elementary stream
45、 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 packet in which the splice_countdown reach
46、es 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, using an appropriate splicer equipment. Bit-stream splicing is applied directly to bit streams where possible splice po
47、ints 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 seamless switching can not be realized. The splicing device based on this approach can be imple
48、mented without any re-encoding processing. Other splicing approaches which do not require any constraints on bit-stream splice points are described in the appendices. J.189F03TS packet ATS packet BOutputbit streamSwitching pointSwitching pointPossible splice points in TSFigure 3/J.189 Bit-stream spl
49、icing 4.3 Transport mechanism of scheduling information for splicing devices 4.3.1 Basic mechanism based on ITU-T Rec. J.181 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 information section notifies the splicing device of scheduled splice events prior to the arrival of splice points, and enables the splicing device to ensu
