JPEG2000 Enables Wireless HD Video Distribution in the Home
Transcript of JPEG2000 Enables Wireless HD Video Distribution in the Home
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JPEG2000 Enables Wireless HDVideo Distribution in the Home
JPEG2000 Is Ideal for Wireless Video• Lowlatency—lessthanoneframe
• MorerobusttoerrorsthanMPEG-X
• Errorresiliencyincreasesrange
• Fixedbitratesimplifiesdesign
JPEG2000 Is Ideal for Consumer Applications• Capableofreal-timeHDcompression
• Symmetricencodeanddecode
• Lowcost,lowcomplexity
• Noexternalmemoryrequired
JPEG2000 Code Stream Is Scalable for Resolution and Quality• Singleencodedstreamcansupplydifferentresolutiondisplays
• Freethumbnailimagesavailable
• Dynamicallyadjustablebitrate:tradequalityforbandwidth
• Reducefilesizebyreducingquality,withouttranscoding
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Frequently Asked Questions
Q: Since most video reaches the home as MPEG-2, why not just send it wirelessly?
A: (NotethatalthoughMPEG-2isusedinthisFAQ,thesameprinciplesapplytoanswersforanytemporalscheme.)MostMPEG-2videostreamsarealreadydecodedbeforebeingsenttotheTVforvariousreasons:toaddmenuoverlays,programguides,etc.Thisistrueformostset-topboxes,DVDplayers,anddigitalbroadcastreceivers.ThevideoistheneithersenttotheTVinanuncompressedformatorisrecompressedusinganinexpensiveencoder(forSDresolution).
Somevideosourcesaren’tencodedinMPEG-2,orthereisnoaccesstotheMPEG-2signal.OutputsfromPCsandmanyDVDplayersfeatureuncompressedanalogordigitalvideoformats,suchasDVIandHDMI.ThesewillhavetobecompressedinrealtimebeforebeingwirelesslytransmittedfromaPCorDVDplayertoadisplay.Thecostofareal-timeHDMPEG-2encoderisroughly$20,000;clearlythisisnotasolutionintendedfortheconsumermarket.
JPEG2000permitslowcost,real-timecompressionofHDvideo,enablinginteractiveapplicationsandthetransmissionofmenuoverlays.
Q: If I do have access to the MPEG-2 stream, why not send it wirelessly?
A: Thevideocommunityhasidentifiedtwomajorproblemswithvideoinwirelessenvironments:errorresiliencyandlatency.Unlesstheapplicationisinteractive,latencyislessofanissuethanerrorresiliency.
AnerrorinanI-frameisvisiblethroughtheentiregroupofpictures(GOP),soasingletransmissionerrorcanresultinseveralframescontainingerrors,creatingdisturbingartifacts.JPEG2000compresseseachframeindividually,soerrorsdonotpropagateacrossframes.Also,JPEG2000isawavelet-basedscheme,anderrorsinthecodestreamtendto“soften”thepicture,notcreateblockyartifacts.AlthoughJPEG2000isadigitalcompressionscheme,itoffersananalog-likegracefuldegradationofimagequality.
Q: Why not use MPEG-2 I-frame-only transmission? That way errors wouldn’t propagate across multiple frames.
A:Thisrequiresreal-timecompression,andwhilereal-timeMPEG-2encodersdoexist,real-timeHDMPEG-2encodersareveryexpensiveandcomplex.Likemostcompressionschemes,MPEG-2wasdesignedtobemorecomplexontheencodesidethanthedecode;MPEG-2simplywasn’tintendedforuseinhighvolumeencodeapplications.
Let’ssuppose,though,thatreal-timeHDI-frame-onlyMPEG-2encodingisfeasible.I-frame-onlyMPEG-2streamsaremuchhigherbandwidththantypicalstreamsandrequiresubstantiallymoreresourcestodecode.MostMPEG-2decodersaren’tbuilttohandlethesebandwidths.Newdecoderswouldhavetobedeployed,andtheywouldbesubstantiallymorecomplexandexpensivethanexistingdecoders.
Q: Doesn’t JPEG2000 consume a lot more bandwidth than MPEG-2?
A: Actualefficiencyisdifferentdependingonwhetherthetransmissionchanneliserror-free(wired)ornoisy(wirelessorpowerline).Inawiredchannelwithnoerrors,JPEG2000consumesabouttwicethebandwidthasMPEG-2forSDandHDvideo,atsimilarqualitylevels.ForcableTVbroadcastorDVDcompression,JPEG2000isnotcompetitivewithMPEG-2.However,asimageresolutionincreasesto1080pandbeyond,MPEG-2becomeslessandlessefficient.MPEG-2encodecomplexityincreasesexponentiallyastheimagesizeincreases,butJPEG2000complexityisroughlylinear.Atsomepoint,JPEG2000becomesmoreefficient,whichisonereasonitwaschosenbytheDigitalCinemaInitiative.It’salsoworthnotingthatJPEG2000canperformlosslesscompression,whichmaybeattractiveinhighendwiredandwirelessHDtransmissions.Forsimilarqualityinanerror-freetransmissionenvironment,anSDMPEG-2streamrequiresabout3Mbps;theequivalentJPEG2000streamwouldbeabout6Mbps.Similarly,720pHDMPEG-2streamrequiresabout16Mbps;theequivalentJPEG2000streamofthesamevideowouldconsumeabout30Mbps.
Inawirelessenvironment,JPEG2000becomesmuch,muchmoreattractive.BecauseMPEG-2manifestserrorsasveryobviousartifacts,muchmoreforwarderrorcorrection(FEC)isrequired,andmanymorepacketsmayhavetoberetransmitted.FECandretransmissionbothconsumebandwidth,requiringalargeframebufferwithcomplexmemoryandtimingconsiderations.OnceFECistakenintoaccount,thebandwidthrequirementsofJPEG2000maybelessthanorequaltothatofanMPEG-2stream.Also,becausethedecodeisstraightforward,theJPEG2000solutionwillbelessexpensive.Further,retransmissionrequiressignificantamountsofbufferonthereceiver,whichcanbecostlyandwhichincreaseslatency.
UsingJPEG2000hasadditionalbenefitsthatarediscussedbelow.Manyofthebenefitsarerelatedtothescalabilityofthecodestream,which,amongotherthings,allowsdisplaysofdifferentresolutionstodecodeonlytheportionsofthecodestreamstheyneed.
UWBprovidesamplebandwidthforJPEG2000,andallowstheotherbenefitsofJPEG2000toberealized.
Q: Why don’t we just wait for H.264? It’s going to address all of these problems, right?
A:H.264promisesbettercompressionefficiency,buttherearenoadvantagesoverMPEG-2forwirelessapplications.Likeanymotionestimationscheme,anyerrorswillbepropagatedthroughoutseveralframes.
Further,forrecompressioninthehome(caseswherethestreamdidn’toriginateinH.264)theencoderwouldrequiretoomuchspaceandcosttoomuchforanyconsumerproduct.Today,H.264HDencodersareprohibitivelyexpensiveforconsumerelectronicsapplications.
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Q: Why not just make the wireless environment more robust?
A: Eveninarobustenvironmenterrorswilloccur.Forwarderrorcorrectionisacriticalpartofqualityofservice(QoS),butitconsumesbandwidth.UsinglessbandwidthonFECmeansitcanbeusedelsewhere.
Q: What about security? Is there content protection for JPEG2000?
A: ThesamequestionsapplytoJPEG2000astheydotoMPEG-2orH.264,oranyothercompressedvideo.Itisverypossibletoapplyacontentprotectionscheme,suchasHDCPorAES128,toacompressedstream.Sincetheinputtoallvideocompressioncodecsisuncompressedvideo,thecontentprotectionmustbeappliedaftercompression,notbefore.Atthepresenttime,manywirelesschipvendorsuseAES128.Recently,SandiaNationalLabsused256-bitAESencryptiontosecurereal-timelive-streamingvideoimagesoverawirelessUWBlinkformilitaryapplications.
SomefeaturesofJPEG2000maymakeiteasiertoapplyexistingencryptionmethods.ThefixedoutputbitrateofJPEG2000shouldmakeiteasiertoimplementhandshakingandothertiming-criticalelementsofcontentprotection.Theintraframe-onlycompressionmayalsoeasesystemdesignrequirements.
Q: How do UWB and JPEG2000 enable wireless HD gaming? Why can’t MPEG-2 be used?
A: Thevideofromagamingconsolemustbecompressedinrealtimebeforebeingwirelesslytransmitted.JPEG2000providesbetterimagequalitythanMPEG-2forreal-timecompressionofeitherSDorHDatthepricepointsofinterest.
Real-timecompressionisnotthesamethingaslowlatency.Becauseitmustwaitforseveralcompressedframestodisplayasingledecompressedframe,MPEG-2hashighlatency.LatencyandbandwidthcanbetradedbygoingtoI-frameonly,but,asdiscussedearlier,thisisanexpensive,complexpropositionevenforSD;recallthatreal-timeHDMPEG-2encodersarethousandsofdollars.
ThelatencyofaJPEG2000streamisaboutoneframeforencodeandoneframefordecode.ThetotallatencyoftheHDgameshownatCES2006,usingAnalogDevices’ADV202andPulse~LINK’sCWave™UWBtechnology,islessthan200ms—theusercan’ttellthatit’sawirelessvideolink.
Q: What is meant by “scalable” quality and resolution?
A: Forquality,scalabilitymeansthatthecompressedcodestreamisorganizedsothatdifferentqualitylevelscanbeextractedwithoutdecompression.JPEG2000willproducethebestpossibleimagefortheavailablebandwidth.Ifthechannelis50Mbps,JPEG2000producesthebestpossibleimagequalityfor50Mbps.Ifthebandwidthdropsto25Mbps,JPEG2000willautomaticallyproducethebestpossibleimagequalityfor25Mbps.Becauseit’sintraframe-onlycompression,theoutputbitratecanbeinstantaneouslyadjustedtomatchchannelconditions.
Qualityscalabilityalsomeansthatportionsofthecodestreamcanbeselectivelyprotected.LikeMPEG-2,theheaderoftheJPEG2000codestreamisthemostimportantsectionanderrorstothissectioncanbemitigatedusingFEC.UnlikeMPEG-2though,somesectionsoftheJPEG2000streamaremoreimportantthanothersandFECcanbeappliedonlytothosesections.Ifthesectionofthepacketcontainingveryhighdetailislostordamaged,theimagewillnotsufferasmuchasifthelowfrequencyportionisdisrupted.Becauseofthis,JPEG2000makesmoreefficientuseofFECbandwidththandoesMPEG-2.
Forresolution,scalabilitymeansthatthecompressedcodestreamisorganizedsothatdifferentresolutionlevels(imagesizes)canbeextractedwithoutdecompression.Anyreceivercandecodejusttheportionofthecodestreamitrequires,allowingittodisplayitsnativeresolution.ThesameJPEG2000codestreamcouldbebroadcasttoanHDTV,anSDTV,adisplayinaremotecontrol,oraPDAwithidealresults.Fortemporalschemesthisisnotpossible;thehighestresolutionmustbedecodedbyeachdevicebefore,whichcouldbeveryexpensiveforHDtemporaldecoders.
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