ISO11172-3MPGAUDIO教学资料.doc
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1、Good is good, but better carries it.精益求精,善益求善。ISO11172-3MPGAUDIO-TITLEPAGEPROVIDEDBYISOCD11172-3CODINGOFMOVINGPICTURESANDASSOCIATEDAUDIOFORDIGITALSTORAGEMEDIAATUPTOABOUT1.5MBIT/sPart3AUDIOCONTENTSFOREWORDINTRODUCTION1.GENERALNORMATIVEELEMENTS1.1Scope1.2OrganizationoftheDocument1.3NormativeReferences
2、2.TECHNICALNORMATIVEELEMENTS2.1Definitions2.2SymbolsandAbbreviations2.3MethodofDescribingBitstreamSyntax2.4Requirements2.4.1CodingStructureandParameters2.4.2SpecificationoftheCodedAudioBitstreamSyntax2.4.3SemanticsfortheAudioBitstreamSyntax2.4.4TheAudioDecodingProcess2.4.5ComplianceRequirements3-Ann
3、exA(normative)Diagrams3-AnnexB(normative)Tables3-AnnexC(informative)TheEncodingProcess3-AnnexD(informative)PsychoacousticModels3-AnnexE(informative)BitSensitivitytoErrors3-AnnexF(informative)ErrorConcealment3-AnnexG(informative)JointStereoCodingFOREWORDThisstandardisacommitteedraftthatwassubmittedfo
4、rapprovaltoISO-IEC/JTC1SC29on22November1991.ItwaspreparedbySC29/WG11,alsoknownasMPEG(MovingPicturesExpertGroup).MPEGwasformedin1988toestablishastandardforthecodedrepresentationofmovingpicturesandassociatedaudiostoredondigitalstoragemedia.Thisstandardispublishedinfourparts.Part1-systems-specifiesthes
5、ystemcodinglayerofthestandard.Itdefinesamultiplexedstructureforcombiningaudioandvideodataandmeansofrepresentingthetiminginformationneededtoreplaysynchronizedsequencesinreal-time.Part2-video-specifiesthecodedrepresentationofvideodataandthedecodingprocessrequiredtoreconstructpictures.Part3-audio-speci
6、fiesthecodedrepresentationofaudiodata.Part4-conformancetesting-isstillinpreparation.ItwillspecifytheproceduresfordeterminingthecharacteristicsofcodedbitstreamsandfortestingcompliancewiththerequirementsstatedinParts1,2and3.InPart1ofthisstandardallannexesareinformativeandcontainnonormativerequirements
7、.InPart2ofthisstandard2-AnnexA,2-AnnexBand2-AnnexCcontainnormativerequirementsandareanintegralpartofthisstandard.2-AnnexDand2-AnnexEareinformativeandcontainnonormativerequirements.InPart3ofthisstandard3-AnnexAand3-AnnexBcontainnormativerequirementsandareanintegralpartofthisstandard.Allotherannexesar
8、einformativeandcontainnonormativerequirements.INTRODUCTIONToaidintheunderstandingofthespecificationofthestoredcompressedbitstreamanditsdecoding,asequenceofencoding,storageanddecodingisdescribed.EncodingTheencoderprocessesthedigitalaudiosignalandproducesthecompressedbitstreamforstorage.Theencoderalgo
9、rithmisnotstandardized,andmayusevariousmeansforencodingsuchasestimationoftheauditorymaskingthreshold,quantization,andscaling.However,theencoderoutputmustbesuchthatadecoderconformingtothespecificationsofclause2.4willproduceaudiosuitablefortheintendedapplication.FigureI-1SketchofabasicencoderInputaudi
10、osamplesarefedintotheencoder.Themappingcreatesafilteredandsubsampledrepresentationoftheinputaudiostream.Themappedsamplesmaybecalledeithersubbandsamples(asinLayerI,seebelow)ortransformedsubbandsamples(asinLayerIII).Apsychoacousticmodelcreatesasetofdatatocontrolthequantizerandcoding.Thesedataarediffer
11、entdependingontheactualcoderimplementation.Onepossibilityistouseanestimationofthemaskingthresholdtodothisquantizercontrol.Thequantizerandcodingblockcreatesasetofcodingsymbolsfromthemappedinputsamples.Again,thisblockcandependontheencodingsystem.Theblockframepackingassemblestheactualbitstreamfromtheou
12、tputdataoftheotherblocks,andaddsotherinformation(e.g.errorcorrection)ifnecessary.LayersDependingontheapplication,differentlayersofthecodingsystemwithincreasingencodercomplexityandperformancecanbeused.AnISOMPEGAudioLayerNdecoderisabletodecodebitstreamdatawhichhasbeenencodedinLayerNandalllayersbelowN.
13、LayerI:Thislayercontainsthebasicmappingofthedigitalaudioinputinto32subbands,fixedsegmentationtoformatthedataintoblocks,apsychoacousticmodeltodeterminetheadaptivebitallocation,andquantizationusingblockcompandingandformatting.LayerII:Thislayerprovidesadditionalcodingofbitallocation,scalefactorsandsamp
14、les.Differentframingisused.LayerIII:Thislayerintroducesincreasedfrequencyresolutionbasedonahybridfilterbank.Itaddsadifferent(nonuniform)quantizer,adaptivesegmentationandentropycodingofthequantizedvalues.JointStereocodingcanbeaddedasanadditionalfeaturetoanyofthelayers.StorageVariousstreamsofencodedvi
15、deo,encodedaudio,synchronizationdata,systemsdataandauxiliarydatamaybestoredtogetheronastoragemedium.Editingoftheaudiowillbeeasieriftheeditpointisconstrainedtocoincidewithanaddressablepoint.Accesstostoragemayinvolveremoteaccessoveracommunicationsystem.Accessisassumedtobecontrolledbyafunctionalunitoth
16、erthantheaudiodecoderitself.Thiscontrolunitacceptsusercommands,readsandinterpretsdatabasestructureinformation,readsthestoredinformationfromthemedia,demultiplexesnon-audioinformationandpassesthestoredaudiobitstreamtotheaudiodecoderattherequiredrate.DecodingThedecoder,subjecttotheapplication-dependent
17、parametersofclause2.4.1,acceptsthecompressedaudiobitstreaminthesyntaxdefinedinclause2.4.2,decodesthedataelementsaccordingtoclause2.4.3,andusestheinformationtoproducedigitalaudiooutputaccordingtoclause2.4.4.FigureI-2SketchofthebasicstructureofthedecoderBitstreamdataisfedintothedecoder.Thebitstreamunp
18、ackinganddecodingblockdoeserrordetectioniferror-checkisappliedintheencoder(seeclause2.4.2.4).Thebitstreamdataareunpackedtorecoverthevariouspiecesofinformation.Thereconstructionblockreconstructsthequantizedversionofthesetofmappedsamples.TheinversemappingtransformsthesemappedsamplesbackintouniformPCM.
19、1.GENERALNORMATIVEELEMENTS1.1ScopeThisstandardspecifiesthecodedrepresentationofhighqualityaudioforstoragemediaandthemethodfordecodingofhighqualityaudiosignals.TheinputoftheencoderandtheoutputofthedecoderarecompatiblewithexistingPCMstandardssuchasstandardCompactDiscandDigitalAudioTape.Thisstandardisi
20、ntendedforapplicationtodigitalstoragemediaprovidingatotalcontinuoustransferrateofabout1.5Mbit/secforbothaudioandvideobitstreams,suchasCD,DATandmagneticharddisc.Thestoragemediamayeitherbeconnecteddirectlytothedecoder,orviaothermeanssuchascommunicationlinesandtheISO11172multiplexstreamdefinedinPart1of
21、thisstandard.Thisstandardisintendedforsamplingratesof32kHz,44.1kHz,and48kHz.1.2ReferencesThefollowingstandardscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthisInternationalStandard.Atthetimeofpublication,theeditionsindicatedwerevalid.Allstandardsaresubjecttorevision,andpar
22、tiestoagreementsbasedonthisInternationalStandardareencouragedtoinvestigatethepossibilityofapplyingthemostrecenteditionsofthestandardsindicatedbelow.MembersofIECandISOmaintainregistersofcurrentlyvalidInternationalStandards.RecommendationsandreportsoftheCCIR,1990XVIIthPlenaryAssembly,Dusseldorf,1990Vo
23、lumeXI-Part1BroadcastingService(Television)Rec.601-1Encodingparametersofdigitaltelevisionforstudios.VolumeXRec.953Encodingparametersofdigitalaudio.IEEEDraftStandardSpecificationfortheimplementationof8x8inversediscretecosinetransform.P1180/D2,July18,19902.TECHNICALNORMATIVEELEMENTS2.1DefinitionsForth
24、epurposesofthisInternationalStandard,thefollowingdefinitionsapply.ACcoefficient:AnyDCTcoefficientforwhichthefrequencyinoneorbothdimensionsisnon-zero.accessunit:inthecaseofcompressedaudioanaccessunitisanaudioaccessunit.Inthecaseofcompressedvideoanaccessunitisthecodedrepresentationofapicture.Adaptives
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