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.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
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