Axis Q1775 - H.264 Video Compression; Bitrate Management

AXISQ1775NetworkCamera
VideoandAudio
•Maximumframerate.Toavoidbandwidthproblems,theframerateallowedtoeachviewercanbeLimitedtoaxed
amount.Alternatively,theframeratecanbesetasUnlimited,whichmeanstheAxisproductalwaysdeliversthehighest
frameratepossibleunderthecurrentconditions.
•Overlaysettings.SeeAboutoverlaytextonpage22.
ClickSavetoapplythenewsettings.
AboutH.264
H.264,alsoknownasMPEG-4Part10/AVC,isavideocompressionstandardthatprovideshighqualityvideostreamsatlowbitrates.
AnH.264videostreamconsistsofdifferenttypesofframessuchasI-framesandP-frames.AnI-frameisacompleteimage,whereas
P-framesonlycontainthedifferencesfrompreviousframes.
AboutGOPlength
AGroupofPictures(GOP)containsoneI-framefollowedbyanumberofP-frames.TheGOPlengthisthenumberofframes
betweentwoI-frames.
IfyousettheGOPlengthandtheframerateequallyyouwillgetoneGOPpersecond.IfyouchangetheGOPlengthtoahigher
valueyouwillgetmoresmallsizedP-framesandlessbigsizedI-frameswhilekeepingthesameframerate.Inotherwords,ahigh
GOP-lengthvaluesavesbandwidth,butthevideoqualitymaydecrease.AlowGOP-lengthvalueincreasesthevideoquality
butneedsmorebandwidth.
AboutH.264proles
TheAxisproductsupportsthefollowingH.264prole(s):
•Baseline:UsetheBaselineproleiftheclientdoesnotsupportCABACentropycoding.
•Main:TheMainproleusesCABACandprovidesabettercompressionwithmaintainedvideoquality.Itrequiresalarger
amountofprocessingpowertodecodethantheBaselineprole.
•High:TheHighproleprovidesahighercompressionthanbothMainandBaselineproles,butrequiresmoreprocessing
powertodecode.Highprolesupports8x8blocks,whichreducesthebitratefurthercomparedtotheMainprole.
Aboutbitratecontrol
Bitratecontrolisusefultomakesurethevideostreamingdoesnottakeuptoomuchbandwidth.
Thebuilt-inbitratecontrolcanbecombinedwithZipstream,seeAboutZipstreamonpage19.Werecommendusingahighbitrate
limittoenablethefullpotentialofZipstream.
Aboutvariablebitrate
Variablebitrate(VBR)adjuststhebitrateaccordingtotheimagecomplexity.Whentheactivityinthesceneincreases,VBRadjusts
thebitrateaccordingtothecomplexity,usingupmorebandwidthforincreasedactivityinthescene,andlessforlowersceneactivity.
Variablebitrateissuitableifthereisasurplusinbandwidth,wheretheincreasedbitratemaynotbeanissue.
Aboutmaximumbitrate
Ifyouhavelimitedbandwidth,werecommendMaximumbitrate(MBR).MBRallowsyoutosetatargetbitratetocontrolthe
bandwidthconsumption.Thetargetvaluelimitsthebitrate,butitmaintainsaexibilitytobeabletoprioritizeacontinuousvideo
stream.Consequently,theframeratemightneedtogodownandtheimagequalitymightdecrease.Topartlycompensateforthis,
youcanselectwhichvariableshallbeprioritized.Notsettingaprioritymeansthatframerateandimagequalityareequallyaffected.
HowtosetanH.264prole
1.TochangethesettingsforallH.264streamsthatdonotuseastreamprole,gotoVideo&Audio>VideoStream>H.264.
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