1、Rec. ITU-R BT.1209-1 1RECOMMENDATION ITU-R BT.1209-1SERVICE MULTIPLEX METHODS FOR DIGITAL TERRESTRIALTELEVISION BROADCASTING(Question ITU-R 121/11)(1995-1997)Rec. ITU-R BT.1209-1The ITU Radiocommunication Assembly,consideringa) that digital terrestrial television broadcasting (DTTB) will be introduc
2、ed in the VHF/UHF bands by someadministrations;b) that existing television broadcast systems are capable of transmitting video, sound and data services which caninclude multi-language services, teletext, Power Distribution Centres (PDC), etc.;c) that digital television broadcasting systems can provi
3、de for the simultaneous transmission of video, sound, dataand control signals;d) that any service multiplex method should provide for the optional capability of multiple digital televisionprogramme services within an existing channel;e) that the service multiplex, for example, can be implemented usi
4、ng structured transmission (fixed assignedmethod), packet transmission (variable assigned method), or a combination of the two;f) that there are significant advantages in each of the above approaches depending upon the service requirements;g) that it may be desirable to support the transmission of a
5、 hierarchical video service (comprising HDTV, EDTVand SDTV) within a single channel;h) that it is desirable that the service multiplex be capable of flexible allocation of data to audio, video and dataservices, consistent with the data capacity required for the video;j) that multiple digital televis
6、ion programme satellite broadcasting systems are under development in somecountries;k) that it is desirable to seek commonality between systems designed for different channel widths,recommends1 that DTTB systems should use the Transport Stream multiplexing methods specified in the InternationalOrgan
7、ization for Standardization/International Electrotechnical Commission Standard 13818-1 (ISO/IECStandard 13818-1). The outline of the specifications is shown in Annex 1.ANNEX 11 IntroductionThe multiplexing scheme specified by ISO/IEC Standard 13818-1 is based on a fixed packet length transport strea
8、mapproach. The packet is called the Transport Stream Packet (TSP).The overall system multiplexing approach can be thought of as a combination of multiplexing at two different layers. Inthe first layer, single program transport bit streams are formed by multiplexing transport packets from one or more
9、elementary bit streams, and in the second layer, a number of single program transport bit streams are combined to form asystem of programs. The function that contains both this program and system level multiplexing information is called theProgram Specific Information (PSI).2 Rec. ITU-R BT.1209-11.1
10、 Single program transport streamA single program transport bit stream is formed by multiplexing individual transport packetized elementary bitstreams (PESs) sharing a common time-base, and a packetized control bit stream that describes the program. Individualbit streams are identified by their uniqu
11、e packet identifiers (PIDs). The organization of this multiplexing function isillustrated in Fig. 1. The control bit stream contains the program_map_table (PMT) that includes information aboutthe PIDs of the transport streams that make up the program, the identification of the applications that are
12、beingtransmitted on these bit streams and the relationship among these bit streams.1209-01PID 1PID 2PID (n + 1)PID nPID (n 1)PID (k + 1)FIGURE 1Illustration of the multiplex function to form a single program transport streamSingle program transport bit stream* A single program could also contain mul
13、tiple video streams.MultiplexerElementary stream 1 (Video)*Elementary stream 2 (Audio 1)Elementary stream k + 1 (Audio k)Elementary stream n 1(Data i)Elementary stream n (Data j)program_map_tableFIGURE 1/BT.1209-1.D01 = 3 CM1.2 System multiplexThe system layer of multiplexing is illustrated in Fig.
14、2. In addition to the single program transport bit streams (with thecorresponding PIDs) that define the individual programs, a system level control bit stream with PID = 0 is defined. Thisbit stream carries the program_association_table (PAT) that maps program_identities to the PIDs of the bit strea
15、mscontaining the program_map_table for the particular program.1209-02Program transport stream 1Program transport stream 2Program transport stream 3Program transport stream 4Program transport stream 5program_association_table PID = 0Multiplexer System level multiplexFIGURE 2Illustration of the multip
16、lex function to form the system level bit streamFIGURE 2/BT.1209-1.D02 = 3 CMThe packet on this system level multiplexing is called the TSP.The TSP and PES are described in detail in 2, and the actual ways to multiplex data services are shown in 3.Rec. ITU-R BT.1209-1 32 Packet format2.1 Transport p
17、acketThe transport packet format is shown in Fig. 3. Transport packets, 188-byte long, containing program transport streams,are generated and asynchronously multiplexed with a single bit stream channel. Each transport packet carries databelonging to one particular “data source” and these sources are
18、 identified from PIDs within the header (which are furtherspecified using information in PSI tables). Data sources are either the applications generating the PESs, or the typesof PSI information being transmitted.1209-03PCR OPCRPCR OPCR11 1 1 18 1 1 1 13 2 2 481 11511522 4 3res42+ res642+ res68 8 81
19、115FIGURE 3Structure of the transport stream188 bytesTransportpacket streamHeader Payload Header Payload Header Payload5 flagsOptionalfieldsstuffing_bytesFlagsNumber of bytesFlagsAdaptationfieldPIDDTS_next_access_unitsync_bytetransport_error_indicatorpayload_ unit_start_indicatortransport_prioritytr
20、ansport_scrambling_controlAdaptationfieldcontrolcontinuity_counteradaptation_field_lengthdiscontinuity_indicatorrandom_access_ indicatorelementary_ stream_priority_indicatorsplice_count_downTransportprivate_data_lengthTransportprivate_dataadaptation_field_extension_lengthLegal timewindow (ltw)piecew
21、ise_rateSeamlessspliceltw_valid_flagltw_offsetpiecewise_ratesplice_typeTransportprivate dataAdaptationfield extensionSplicing pointFIGURE 3/BT.1209-1.D03 = 3 CM2.1.1 Headersync_byte (8 bits): it is for packet synchronization, and sent in every packet.transport_error_indicator (1 bit): a flag to show
22、 if the packet contains error bits or not. This field can beused for error handling.4 Rec. ITU-R BT.1209-1payload_unit_start_indicator (1 bit): a flag to show if a PES starts in the packet or the first byte of a PSIsection is included in the packet or not.transport_priority (1 bit): this flag shows
23、the priority of the packet. It can be used to indicate thatthe packet was sent repeatedly to increase robustness against transmissionerror and has less priority.PID (13 bits): an identifier for the TSP.transport_scrambling_control (2 bits): “00” means “not scrambled” and the others mean “user define
24、d”. “10”and “11” can be used as “scrambled with key A” and “scrambled withkey B”, respectively.continuity_counter (4 bits): it shows the order of transmitted packets having the same PID. Errordetection is enabled in the decoder through the use of this field.2.1.2 Adaptation field (variable length)ad
25、aptation_field_length (8 bits): it shows the byte length of the contents of the adaptation field.discontinuity_indicator (1 bit): it indicates the discontinuity of PCR.random_access_indicator (1 bit): it indicates that the next PES packet of the same PID contains anelementary stream access point. Th
26、is is used for the random entry intoapplication bit streams in such case as programme tuning or channelchange.elementary_stream_priority_indicator (1 bit): this flag can be used to indicate that the same elementary stream is sentrepeatedly to increase robustness against transmission error and has le
27、sspriority.5 flags (5 bits).2.1.3 Optional fieldsprogram_clock_reference (PCR)(42 bits + 6 bits (for future use):the reference data for system clock synchronization. It consists of 33 bitfield which is expressed by 90 kHz and 9 bit extension field which isexpressed by 27 MHz.original_program_clock_r
28、eference (OPCR)(42 bits + 6 bits (for future use):it assists in the reconstruction of a single TS from another TS.splice_count_down (8 bits): it indicates the number of TSPs until or after a splicing point. It isnecessary to note that when this is used in a high-speed system, thecontrol needs to sta
29、rt just before the discontinuous point (several ms inthe HDTV case, for example). This shows the points in the elementary bitstreams at which local programme insertion such as commercials isallowed.private_data_length (8 bits): it shows the byte length of the private data.private_data: users can use
30、 these bit streams for themselves.adaptation_field_extension_length (8 bits): it shows the byte length of the following optional fields.3 flags (3 bits).ltw_valid_flag (1 bit): it indicates that the value of the ltw_offset is valid.ltw_offset (15 bits): it indicates the displacement in the arrival t
31、ime of the TSP.piecewise_rate (22 bits): it specifies the bit rate over all transport packets of this PID measured inunits of 50 bytes/s.splice_type (4 bits): it is used to derive splice_decoding_delay and max_splice_rate fromtables in the specifications.DTS_next_access_unit (33 bits): it indicates
32、the value of the DTS (decoding time stamp) explained in 2.2.3 of the next access unit of an unspliced or seamless spliced stream.Rec. ITU-R BT.1209-1 52.1.4 Stuffingstuffing-bytes (8X bytes): for stuffing.2.2 PES packetThe structure of the PES packet is shown in Fig. 4. The PES packet consists of th
33、e header, and the followed elementarystream of video or audio signals standardized in the Moving Pictures Expert Group (MPEG) or the elementary stream fordata services, and its length is variable. Namely, both the header and the content of the packet are variable.1209-04211111133 33111131ESCRPTSDTSP
34、TSPTS/DTS ESCRPESCRC24 8 16733 2 42 22816m 822 1 11 188n 8128 8 7 1 6 14 7FIGURE 4Structure of the PES packet(Marker bits are not shown.)OptionalPESheaderPES packet data bytes7 flagsOptionalfieldsstuffing_bytes(0 FF)FlagsFlagslengthNo. of bytesPES_packet_length“ID”PES_scrambling_ controldata_alignme
35、nt_indicatorCopyrightoriginal_or_copyPES_header_data_lengthPES_prioritypacket_ start_code_prefixstream_idPES_extensionFlag 2P-STD_bufferprogram_packet_sequence_counterpack_header_fieldPESprivate_dataPESextensionprevious_PES_CRCadditional_copy_infoDSM_trick_modeES_ratePESprivate_datapack_ header_fiel
36、dprogram_packet_sequence_counterMPEG1MPEG2idOriginalstuff lengthP-STD_bufferPES_extension_field_lengthPES_extension_field_dataES_rateDSM_trick_modeadditional_copy_infoPESextensionFIGURE 4/BT.1209-1.D04 = 3 CM6 Rec. ITU-R BT.1209-12.2.1 PES headerpacket_start_code_prefix (24 bits): a fixed 24-bit pat
37、tern indicates the start of the PES packet.stream_id (8 bits): it is used for identifying each PES. The 4th bit is available for videosignals and the 5th bit for audio signals, and the 11 kinds of data servicecan be identified. Although it is impossible to predict the number ofidentifications for th
38、e future services, the PES_extension_field allows itto increase, and one example is explained in the third section.PES_packet_length (16 bits): it shows the byte length of the contents of the packet.2.2.2 Optional PES headerPES_scrambling_control (2 bits): “00” means “not scrambled” and the others m
39、ean “user defined”.PES_priority (1 bit): it indicates the priority of the payload of the PES packet. It is not used inthe broadcast stream.data_alignment_indicator (1 bit): it indicates whether the access unit data is aligned after the PES packetheader or not.copyright (1 bit): it indicates whether
40、the material of the associated PES packet payload iscopyrighted or not.original_or_copy (1 bit): it indicates whether the contents of the PES packet payload is an originalor copy.7 flags (8 bits).PES_header_data_length (8 bits): it specifies the total number of bytes of the optional fields and stuff
41、ingbytes contained in this PES packet header.2.2.3 Optional fieldsPTS (presentation_time_stamp)(33 bits):it indicates the intended time of presentation of the presentation unit ofthe first access unit that commences in the packet. The value of PTS ismeasured by 90 kHz.DTS (decoding_time_stamp) (33 b
42、its): it indicates the intended time of decoding of the first access unit thatcommences in the packet. The value of DTS is measured by 90 kHz.ESCR (elementary_stream_clock_reference)(42 bits):it is used in a PES stream, and it is not used for broadcasting.ES_rate (22 bits): it is used in a PES strea
43、m, and it is not used for broadcasting.DSM_trick_mode (8 bits): it is used for digital storage media, and it is not used for broadcasting.additional_copy_info (7 bits): it contains private data relating to copyright information. It needs to bereserved because there will be various kinds of services
44、in broadcasting.previous_PES_CRC (16 bits): the CRC for the previous PES packet is sent in the header of thefollowing PES packet which has the same PID value. It is intended foruse in network maintenance, and it is not intended for use by elementarystream decoders.2.2.4 PES_extension5 flags (5 bits
45、and 3 bits reserved).Rec. ITU-R BT.1209-1 72.2.5 Optional field (variable length)private_data (128 bits): it can be used for future services.pack-header-field (8 bits): it is used when PS is transmitted by TS and the PS is reconstructed at thereceiver, and it is not used for broadcasting.Program_pac
46、ket_sequence_counter(8 bits):it can be used as the continuity counter for the PES packets although it isintended to be used in PS.P-STD_buffer (16 bits): it is used in PS, and it is not used for broadcasting.PES_extension_field_length (7 bits): it means the byte length of the content of the extensio
47、n field.PES_extension_field (variable length): it is used for future extension.3 Scheme for the multiplexing of various dataExamples of a multiplexing scheme of general purpose data are shown in Appendix 1 to Annex 1. An example for theinsertion of teletext into the MPEG-2 transport multiplex is sho
48、wn in Appendix 2 to Annex 1.APPENDIX 1TO ANNEX 1Multiplexing of general purpose data for digital terrestrialtelevision broadcasting1 Scheme for the multiplexing of various dataIn digital TV broadcasting, the specifications should allow the system to transmit various kinds of data service not onlyrel
49、ated but also non-related to the TV programmes.According to ISO/IEC Standard 13818-1, there are two ways to multiplex data. One is to use the elementary streams andthe other is to use the private sections defined in the PSI.1.1 Data multiplexing by PES-type data groupIn this case, the start of each data group is synchronized with the start of the payload of the TSP. The stream_id code isassigned for data services.This scheme is suitable for the data of presentation media which uses the Presentation Time Stamp (PTS).When so-called multimedia broadcasting is carried out,
