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MPEG-2传输流中的PCR分析.docx

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MPEG-2传输流中的PCR分析 Introduction: Inthefieldofdigitalvideobroadcasting,theMPEG-2transportstreamisthestandardinuseglobally.Transportstreamreferstotheformatofamultimediadatawhichplaysanimportantroleinvideotransmission.Withinthismultimediastream,wehavetheProgramClockReference(PCR)insertedattheheadofthepacketofaudioandvideofortimingsynchronization.Inthisarticle,wewilllookatthePCRanalysiswithintheMPEG-2transportstream. MPEG-2TransportStream: MPEG-2TSisaformatthatisusedforsimulationofdigitalvideobroadcasting,satelliteandcabledatadistribution.Thetransmissionofaudioandvideoisdonebytheuseofpacketsthatformthetransportstreams.Thevideoandaudioframeswhicharecontainedinthesetransportstreamsareprocessed,packed,andsentoutaccordingtotherequiredspecifications.ThemainpurposeofMPEG-2TSistotransmitmultipleprogramsthroughonetransportstream. ProgramClockReference(PCR): IntheMPEG-2transportstream,theProgramClockReference(PCR)isasystemclockreferencethatisusedforsynchronizationofvideodecodersandaudiowiththetransportstream.Itistransmittedwiththevideoandaudioheadersofthetransportstreampackets.PCRisalsousedtoprovideinformationaboutthetimingofthedatastream.ToextractthePCR,oneneedstoreadapacketthatcontainsitinthetransportstream.ThePCRisa42-bitvalueencodedinthepacketheaderthatisinsertedbeforetheMPEG-2frameofavideooraudiosequence. PCRAnalysis: PCRanalysisinvolvesthestudyofthePCRvaluesoftheMPEG-2transportstreampackets.TheanalysisoftheProgramClockReferencevaluescanprovideinformationaboutthetimingofthemultimediastream.Inatransportstream,thePCRvaluesareusuallytransmittedatafixedrateof27MHz.ThereceiverordecodercanusePCRreadingstodeterminethetimewhenadatapacketisreceived.Thisensuresthatthedataistransmittedinthecorrectorderandattherightspeed. PCRJitter: PCRJitterreferstothevarianceinthePCRvalues,andcanbemeasuredusingthePCRstandarddeviation.ThestandarddeviationbetweenPCRvaluescanbeusedforidentifyingthevariationsintheTransportStream.PCRJitterisoneofthemainfactorswhichcanaffectthequalityofvideoplayback,asitimpa