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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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AnalogDevicescurrentlyofferstheADV202,aJPEG2000-compliantcodec.MoreinformationontheADV202isavailableat:ftp.analog.com/pub/Digital_Imaging/ADV202_FTP_site_contents_3.html.

Formoreinformation,pleasecontact:BrookeCrossley,HighSpeedConvertersMarketingManagerPhone:336.605.4308Email:brooke.crossley@analog.com

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