User guide

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A.1.1.2 ImpactofPacketLossonSpecificVideoCodecs
AsshowninFigure2‐3,asimplenon‐robustvideostreamcanbeseverelydegraded
withevenlowlevelsofpacketlossduetotheerrorpropagationeffectsdescribedabove.
PeakSignal‐to‐NoiseRatio(PSNR)isanobjectivemeasurementofvideoservice
quality
comparingthemaximumpowerofthevideosignaltothepowerofcorruptingnoiseaffecting
thesignal.Generally,aPSNRofunder20dBisregardedasunwatchable,andthislevelis
reachedforMPEGvideowithalossrateunder1percent.
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Figure2‐3.
EstimatedPSNR
forThree
CommonCodecs
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Errormi
tigationalgorithmsarebeingincreasinglyappliedtohelptocompensateforpacket
loss[11][12].Methodsinclude:
ForwardErrorCorrection(FEC)‐redundancyisappliedtothedatastreamtoallowsome
proportionoflostorerroredpacketstobereplaced