TS流分析标准24翻译版.docx

TS流分析标准24翻译版.docx

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TS流分析标准24翻译版

2.4TransportStreambitstreamrequirements

2.4.1TransportStreamcodingstructureandparameters

TheITU-TRec.H.222.0|ISO/IEC13818-1TransportStreamcodinglayerallowsoneormoreprogramstobecombined

intoasinglestream.Datafromeachelementarystreamaremultiplexedtogetherwithinformationthatallows

synchronizedpresentationoftheelementarystreamswithinaprogram.

TS编码层允许将一个或多个节目组合成一个流。

每个ES的数据由同一个节目中ES的同步表示的信息来复合。

ATransportStreamconsistsofoneormoreprograms.Audioandvideoelementarystreamsconsistofaccessunits.

一个TS是由一个或多个节目组成。

音频和视频的ES是由访问单元（AU）组成。

ElementaryStreamdataiscarriedinPESpackets.APESpacketconsistsofaPESpacketheaderfollowedbypacket

data.PESpacketsareinsertedintoTransportStreampackets.ThefirstbyteofeachPESpacketheaderislocatedatthe

firstavailablepayloadlocationofaTransportStreampacket.

PES包装载有ES数据。

PES包是由包头和包数据组成。

PES包又插入到TS包中。

每个PES包头的第一个字节装载于TS包的第一个有效负载位置。

ThePESpacketheaderbeginswitha32-bitstart-codethatalsoidentifiesthestreamorstreamtypetowhichthepacket

databelongs.ThePESpacketheadermaycontaindecodingandpresentationtimestamps（DTSandPTS）.ThePES

packetheaderalsocontainsotheroptionalfields.ThePESpacketdatafieldcontainsavariablenumberofcontiguous

bytesfromoneelementarystream.

PES包头由一个32位长的起始码开始，它定义了包数据所属的流或流类型。

PES包头还包含有解码和表示时间戳（DTSandPTS）。

PES包头还有其它的可选域。

PES包数据域包含有变长且连续的ES数据字节。

TransportStreampacketsbeginwitha4-byteprefix,whichcontainsa13-bitPacketID（PID）,definedinTable2-2.The

PIDidentifies,viatheProgramSpecificInformation（PSI）tables,thecontentsofthedatacontainedintheTransport

Streampacket.TransportStreampacketsofonePIDvaluecarrydataofoneandonlyoneelementarystream.

TS包由4字节的前缀开始，它包含一个13比特长的包ID（PID）,定义见于Table2-2。

PID的识别要通过PSI表（它被包含在TS包中）。

一个PID的TS包有且只能有一个ES。

ThePSItablesarecarriedintheTransportStream.TherearefourPSItables:

•ProgramAssociationTable;节目相关表

•ProgramMapTable;节目映射表

•ConditionalAccessTable;条件访问表

•NetworkInformationTable.网络信息表

Thesetablescontainthenecessaryandsufficientinformationtodemultiplexandpresentprograms.TheProgramMap

Table,inTable2-28,specifies,amongotherinformation,whichPIDs,andthereforewhichelementarystreamsare

associatedtoformeachprogram.ThistablealsoindicatesthePIDoftheTransportStreampacketswhichcarrythePCR

foreachprogram.TheConditionalAccessTableshallbepresentifscramblingisemployed.TheNetworkInformation

TableisoptionalanditscontentsarenotspecifiedbythisRecommendation|InternationalStandard.

这些表包含了必须而充分的信息来解复用和显示节目。

Table2-28对应的节目映射表指明了哪个PID（也就是哪个ES）对应的是哪个节目。

这个表也同样指明了TS包（它带有每个节目的PCR域）的PID。

条件访问表用于scrambling时。

网络信息表是可选的，它的说明不在本说明书。

TransportStreampacketsmaybenullpackets.NullpacketsareintendedforpaddingofTransportStreams.Theymaybe

insertedordeletedbyre-multiplexingprocessesand,therefore,thedeliveryofthepayloadofnullpacketstothedecoder

cannotbeassumed.

TS包可以是空包。

ThisRecommendation|InternationalStandarddoesnotspecifythecodeddatawhichmaybeusedaspartofconditional

accesssystems.ThisSpecificationdoes,however,providemechanismsforprogramserviceproviderstotransportand

identifythisdatafordecoderprocessing,andtoreferencecorrectlydatawhicharespecifiedbythisSpecification.This

typeofsupportisprovidedboththroughTransportStreampacketstructuresandintheconditionalaccesstable（referto

Table2-27ofthePSI）.

条件访问表的说明不在本文档

2.4.2TransportStreamsystemtargetdecoder

ThesemanticsoftheTransportStreamspecifiedin2.4.3andtheconstraintsonthesesemanticsspecifiedin2.7require

exactdefinitionsofbytearrivalanddecodingeventsandthetimesatwhichtheseoccur.Thedefinitionsneededareset

outinthisRecommendation|InternationalStandardusingahypotheticaldecoderknownastheTransportStreamSystem

TargetDecoder（T-STD）.InformativeAnnexDcontainsfurtherexplanationoftheT-STD.

TS语义的说明在2.4.3节，对这些语义的限定在2.7节。

TheT-STDisaconceptualmodelusedtodefinethesetermspreciselyandtomodelthedecodingprocessduringthe

constructionorverificationofTransportStreams.TheT-STDisdefinedonlyforthispurpose.Therearethreetypesof

decodersintheT-STD:

video,audio,andsystems.Figure2-1illustratesanexample.Neitherthearchitectureofthe

T-STDnorthetimingdescribedprecludesuninterrupted,synchronizedplay-backofTransportStreamsfromavarietyof

decoderswithdifferentarchitecturesortimingschedules.

Figure2-1–TransportStreamsystemtargetdecodernotation

ThefollowingnotationisusedtodescribetheTransportStreamsystemtargetdecoderandispartiallyillustratedin

Figure2-1above.

i,i′,i″areindicestobytesintheTransportStream.Thefirstbytehasindex0.

jisanindextoaccessunitsintheelementarystreams.

k,k′,k″areindicestopresentationunitsintheelementarystreams.

nisanindextotheelementarystreams.

pisanindextoTransportStreampacketsintheTransportStream.

t（i）indicatesthetimeinsecondsatwhichthei-thbyteoftheTransportStreamentersthesystemtarget

decoder.Thevaluet（0）isanarbitraryconstant.

PCR（i）isthetimeencodedinthePCRfieldmeasuredinunitsoftheperiodofthe27MHzsystemclock

whereiisthebyteindexofthefinalbyteoftheprogram_clock_reference_basefield.

An（j）isthej-thaccessunitinelementarystreamn.An（j）isindexedindecodingorder.

tdn（j）isthedecodingtime,measuredinseconds,inthesystemtargetdecoderofthej-thaccessunitin

elementarystreamn.

Pn（k）isthek-thpresentationunitinelementarystreamn.Pn（k）resultsfromdecodingAn（j）.Pn（k）is

indexedinpresentationorder.

tpn（k）isthepresentationtime,measuredinseconds,inthesystemtargetdecoderofthek-thpresentation

unitinelementarystreamn.

tistimemeasuredinseconds.

Fn（t）isthefullness,measuredinbytes,ofthesystemtargetdecoderinputbufferforelementarystreamn

attimet.

Bnisthemainbufferforelementarystreamn.Itispresentonlyforaudioelementarystreams.

BSnisthesizeofbuffer,Bn,measuredinbytes.

Bsysisthemainbufferinthesystemtargetdecoderforsysteminformationfortheprogramthatisinthe

processofbeingdecoded.

BSsysisthesizeofBsys,measuredinbytes.

MBnisthemultiplexingbuffer,forelementarystreamn.Itispresentonlyforvideoelementarystreams.

MBSnisthesizeofMBn,measuredinbytes.

EBnistheelementarystreambufferforelementarystreamn.Itispresentonlyforvideoelementary

streams.

EBSnisthesizeoftheelementarystreambufferEBn,measuredinbytes.

TBsysisthetransportbufferforsysteminformationfortheprogramthatisintheprocessofbeingdecoded.

TBSsysisthesizeofTBsys,measuredinbytes.

TBnisthetransportbufferforelementarystreamn.

TBSnisthesizeofTBn,measuredinbytes.

DsysisthedecoderforsysteminformationinProgramStreamn.

Dnisthedecoderforelementarystreamn.

Onisthere-orderbufferforvideoelementarystreamn.

RsysistherateatwhichdataareremovedfromBsys.

RxnistherateatwhichdataareremovedfromTBn.

RbxnistherateatwhichPESpacketpayloaddataareremovedfromMBnwhentheleakmethodisused.

Definedonlyforvideoelementarystreams.

Rbxn（j）istherateatwhichPESpacketpayloaddataareremovedfromMBnwhenthevbv_delaymethodis

used.Definedonlyforvideoelementarystreams.

RxsysTherateatwhichdataareremovedfromTBsys.

ResThevideoelementarystreamratecodedinasequenceheader.

2.4.2.1Systemclockfrequency

TiminginformationreferencedintheT-STDiscarriedbyseveraldatafieldsdefinedinthisSpecification.Referto

2.4.3.4and2.4.3.6.InPCRfieldsthisinformationiscodedasthesampledvalueofaprogram’ssystemclock.ThePCR

fieldsarecarriedintheadaptationfieldoftheTransportStreampacketswithaPIDvalueequaltothePCR_PIDdefined

intheTS_program_map_sectionoftheprogrambeingdecoded.

T-STD的时钟信息参考定义在2.4.3.4，2.4.3.6节的多个数据域中，在PCR域中，时钟信息编码成节目的系统时钟的样本值。

而PCR域定义在TS包的PID等于PCR_PID的adaptation域中

Practicaldecodersmayreconstructthisclockfromthesevaluesandtheirrespectivearrivaltimes.Thefollowingare

minimumconstraintswhichapplytotheprogram’ssystemclockfrequencyasrepresentedbythevaluesofthePCR

fieldswhentheyarereceivedbyadecoder.

实际的解码器可能会这些值和期望到达时间来重建时钟。

重建节目的系统时钟频率定义如下。

ThevalueofthesystemclockfrequencyismeasuredinHzandshallmeetthefollowingconstraints:

NOTE–Sourcesofcodeddatashouldfollowatightertoleranceinordertofacilitatecompliantoperationofconsumerrecorders

andplaybackequipment.

Aprogram’ssystem_clock_frequencymaybemoreaccuratethanrequired.Suchimprovedaccuracymaybetransmitted

tothedecoderviatheSystemclockdescriptordescribedin2.6.20.

节目的system_clock_frequency可以比上面描述的精度更高。

这个更高精度可以通过系统时钟描述子（见于2.6.20节）传输给解码器。

BitratesdefinedinthisSpecificationaremeasuredintermsofsystem_clock_frequency.Forexample,abitrateof

27000000bitspersecondintheT-STDwouldindicatethatonebyteofdataistransferredeveryeight（8）cyclesofthe

systemclock.

本说明书中的比特率以system_clock_frequency为单位。

例如，在T-STD中27Mb/s指的是传输一个字节数据需要8个系统时钟。

Thenotation"system_clock_frequency"isusedinseveralplacesinthisSpecificationtorefertothefrequencyofaclock

meetingtheserequirements.Fornotationalconvenience,equationsinwhichPCR,PTS,orDTSappear,leadtovaluesof

timewhichareaccuratetosomeintegralmultipleof（300×233/system_clock_frequency）seconds.Thisisduetothe

encodingofPCRtiminginformationas33bitsof1