Canon XL1 3CCD Camcorder User Manual

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‐Average‐limitedencodingisusedformostprogressivedownloadfileswherefilesizeanddatarate

arethelimitingfactors.



•Peaklimitedencoding‐generallymeantforhardwaredevicesorhigh‐data‐ratecontentwherethe

speedofthedecoder(CPU,memory,ordisk)isthelimitingfactor.

‐Specifyingaparticularpeak‐limiteddataratedoesn’tmeanthepeakofthefilewillactuallybeatthe

requestedbitrate.Instead,thepeak‐limiteddatarateisthemaximumratesupportedbythedecoder,

buttheencoderisfreetousealowerrateifappropriateforthecontent.

‐Peak‐limitedencodingalsoworkswellforhigh‐resolutionandhigh‐data‐ratewebandCDROMfiles

thatneedtoplaybackonlower‐endcomputers.

‐Somecodecssupportencodingwithbothaveragelimitingandpeaklimiting.



•Bufferlimitedencoding‐themethodofchoiceforreal‐timestreaming.

‐Theaveragedatarateisn’tappliedtotheoverallfile,butitisappliedtoany

givensectionofvideo.So,whenvideoisencodedwithathree‐secondbuffer,anyarbitrarythree‐

secondchunkofthefilehasadatarateatorbelowthetargetdatarate.

‐Moststreamingencodedfilesusebothaverage‐limitedandbuffer‐limitedencoding.Buffer‐limited

encodingisoftencalledconstantbitrateorCBR.



•Qualitylimitedencoding‐differentfromtheothermethodsbecauseitdoesn’tspecifyadatarate.

‐Instead,itspecifiesaqualitytarget,andeachframeusesasmanyorasfewbitsneededtoreachthat

qualitytarget.

‐Thismodeisn’tcompatiblewithreal‐timestreaming.However,itcan

workverywellforarchivingcontentorfordownloadingmission‐criticalvideowherequalityismore

importantthanthefilesizeordownloadtime.

‐Mostcodecsthatperformquality‐limitedencodingspecifythequalityona0‐100range.However,

actualvisualqualityproducedbythesamevaluecanwidelyvaryamongcodecs.

‐Somecodecssupportaverage‐limitedandquality‐limitedencodingtogether;thequalitylimitsetsa

minimumqualityforeachframe.Ifaframefallsbelowthequalitylimitbasedonavailablebitrate,the

bitrateforthatframeisraisedsoitmeetstheminimum.

‐Typically,oneormoreframesafterthelow‐qualityframearedroppedtopreservetheaveragebit

rate.

‐Thismodesacrificessmoothmotioninfavorofimagequality.



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Canon XL1 3CCD Camcorder User Manual