Axis Q1942-E - H.264 Features and Bitrate Control

AXISQ1942-EPTMountThermalNetworkCamera
Aboutvideosettings
•Palette.Theimagecanbecoloredbyapplyingapalette.Colorsintheimageindicatetemperaturedifferencesandcanbe
usedtoimprovevisibilityofnedetails.Thepaletteselectedhereisusedasthedefaultpalette,otherpalettescanbe
selectedontheLiveViewpage.
•Maximumframerate.Toavoidbandwidthproblems,theframerateallowedtoeachviewercanbeLimitedtoaxed
amount.Alternatively,theframeratecanbesetasUnlimited,whichmeanstheAxisproductalwaysdeliversthehighest
frameratepossibleunderthecurrentconditions.
•Overlaysettings.SeeAboutoverlaytextonpage20.
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.
EqualvaluesforGOPlengthandframerateresultinoneGOPpersecond.AhigherGOPlengthvalueresultsinmoresmall-sized
P-framesandlessbig-sizedI-frameswhilekeepingthesameframerate.Inotherwords,ahighGOP-lengthvaluesavesbandwidth,
butthevideoqualitymaydecrease.AlowGOP-lengthvalueincreasesthevideoqualitybutrequiresmorebandwidth.
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,seeAboutZipstreamonpage18.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.
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