Canon XL1 3CCD Manual

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Choosingbetweenencodingspeedandquality

‐Manycodecsofferacontrolthatspecifiesatrade‐offbetweenencodingtimeandquality.Thefaster

modestypicallyperformmuchlessexhaustivemotionestimation.‐Generally,bigspeedchangescause

muchsmallerqualitygains

‐Thecorrecttrade‐offbetweenspeedandqualityvariesdependingontheproject.‐ForDVDprojects,

titlesunderanhourwon’tgainmuchbyslower,higher‐qualityencodingbecausethedatarateisso

high.Web‐distributedcontentalmostalwaysbenefitsfromtheslower,high‐qualityencodedfiles,

becausebandwidthissooftenthelimitingfactorforwebvideo.

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Settingframesize

Framesize(alsocalledresolution)istheheightandwidthofthefinalvideoframe,measuredinpixels.

Thedataratechangesinproportiontotheareaoftheframe(heightxwidth).

‐Thus,convertingfrom320x240to640x480wouldrequireaboutfourtimesthedatarate,but

convertingto192x144,youcouldreducethedataratedowntoone‐third.Becausetherearefewer

pixels,pixelqualitybecomesmoreimportant.

‐Mostcodecsandformatsrequiretheheightandwidthofavideotobedivisiblebytwoandgivebest

compressionefficiencywhenheightandwidtharedivisibleby16.

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Specifyingaspectratio

‐Animportantfacetofframesizeisaspectratio.MostwebandCD‐ROMformatsusesquarepixels,

andmanyformatsonlysupportsquarepixels.

‐Conversely,thedisc‐basedVCD,SVCD,andDVDformatsonlyusenonsquarepixels.‐It’simportantto

figureoutthetargetaspectratiofirst,andthenmakesurethattheframesizeyouchoosegivesthe

correctaspectratiogiventhepictureshapeinwhichthecontentisdelivered.

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Adjustingtheframerate

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Higherframeratesappearsmoother,andlowerframeratesappearchoppier.

Anythingbelow20fpsdoesn’tappearsmooth,andbelow10fps,thevideolooksmorelikea

filmstripthanmovingvideo.

Reducingorincreasingtheframeratehasmuchlesseffectthanframesizeonthedatarate

becausereducingtheframeraterequiresencodingtwiceasmuchmotionforeachframe,aprocess

thatrequiresmorebitsforeachframe.Also,eachframeappearsfortwiceaslong,sothere’smore