Video File Format Specification(FLV)

VideoFileFormatSpecificationVersion9Copyright©2008AdobeSystemsIncorporated.Allrightsreserved.Thismanualmaynotbecopied,photocopied,reproduced,translated,orconvertedtoanyelectronicormachine-readableforminwholeorinpartwithoutwrittenapprovalfromAdobeSystemsIncorporated.Notwithstandingtheforegoing,apersonobtaininganelectronicversionofthismanualfromAdobemayprintoutonecopyofthismanualprovidedthatnopartofthismanualmaybeprintedout,reproduced,distributed,resold,ortransmittedforanyotherpurposes,including,withoutlimitation,commercialpurposes,suchassellingcopiesofthisdocumentationorprovidingpaid-forsupportservices.TrademarksAdobe,ActionScript,Flash,FlashMediaServer,andFlashPlayerareeitherregisteredtrademarksortrademarksofAdobeSystemsIncorporatedandmayberegisteredintheUnitedStatesorinotherjurisdictionsincludinginternationally.Otherproductnames,logos,designs,titles,words,orphrasesmentionedwithinthispublicationmaybetrademarks,servicemarks,ortradenamesofAdobeSystemsIncorporatedorotherentitiesandmayberegisteredincertainjurisdictionsincludinginternationally.NorightorlicenseisgrantedtoanyAdobetrademark.Third-PartyInformationThisguidecontainslinkstothird-partywebsitesthatarenotunderthecontrolofAdobeSystemsIncorporated,andAdobeSystemsIncorporatedisnotresponsibleforthecontentonanylinkedsite.Ifyouaccessathird-partywebsitementionedinthisguide,thenyoudosoatyourownrisk.AdobeSystemsIncorporatedprovidestheselinksonlyasaconvenience,andtheinclusionofthelinkdoesnotimplythatAdobeSystemsIncorporatedendorsesoracceptsanyresponsibilityforthecontentonthosethird-partysites.Noright,licenseorinterestisgrantedinanythirdpartytechnologyreferencedinthisguide.NOTICE:THISPUBLICATIONANDTHEINFORMATIONHEREINISFURNISHED“ASIS”,ISSUBJECTTOCHANGEWITHOUTNOTICE,ANDSHOULDNOTBECONSTRUEDASACOMMITMENTBYADOBESYSTEMSINCORPORATED.ADOBESYSTEMSINCORPORATEDASSUMESNORESPONSIBILITYORLIABILITYFORANYERRORSORINACCURACIES,MAKESNOWARRANTYOFANYKIND(EXPRESS,IMPLIED,ORSTATUTORY)WITHRESPECTTOTHISPUBLICATION,ANDEXPRESSLYDISCLAIMSANYANDALLWARRANTIESOFMERCHANTABILITY,FITNESSFORPARTICULARPURPOSES,ANDNONINFRINGEMENTOFTHIRDPARTYRIGHTS.AdobeSystemsIncorporatedPublishedApril2008iContentsIntroduction.............................................1TheFLVfileformat...........................................1TheF4Vfileformat...........................................1Chapter1:TheFLVFileFormat.............................3TheFLVheader................................................4TheFLVfilebody...............................................4FLVtags.......................................................5Audiotags.....................................................6AACAUDIODATA............................................7Videotags.....................................................8AVCVIDEOPACKET..........................................9Datatags......................................................9onMetaData...................................................13Chapter2:TheF4VFileFormat...........................15TheF4Vbox..................................................15ftypbox.......................................................16moovbox.....................................................17mvhdbox.....................................................17trakbox.......................................................19udtabox......................................................19metabox......................................................19mdiabox.....................................................20minfbox.....................................................20stblbox......................................................20tkhdbox......................................................21mdhdbox....................................................22stsdbox.....................................................23stscbox......................................................24sttsbox......................................................25cttsbox......................................................26stcoandco64boxes..........................................26stssbox.......................................................27iiContentsstszbox......................................................28chplbox......................................................28pdinbox......................................................29mdatbox.....................................................30Requiredstructure.............................................30Supportedmediatypes........................................31Unsupportedboxes............................................32Chapter3:F4VMetadata................................33Tagbox......................................................34ilstbox.......................................................34Imagemetadata...............................................35Textmetadata................................................36stylbox....................................................36hlitbox.....................................................37hclrbox....................................................37krokbox....................................................38dlaybox....................................................38drpobox...................................................39drptbox....................................................39hrefbox....................................................39tboxbox....................................................40blnkbox....................................................41twrpbox...................................................411IntroductionThisdocumentprovidestechnicalformatinformationforthevideofileformatssupportedbyAdobe®Flash®Playersoftware—FLVandF4V.Adobeseriouslyconsidersallfeedbacktothevideofileformatspecification.E-mailanyunclearorpotentiallyerroneousinformationwithinthespecificationtoAdobeatflashformat@adobe.com.AllsuchemailsubmissionsshallbesubjecttotheSubmittedMaterialsguidelinesintheTermsofUseatwww.adobe.com/misc/copyright.html.TheFLVfileformatStartingwithSWFfilespublishedforFlashPlayer6,FlashPlayercanexchangeaudio,video,anddataoverRTMPconnectionswiththeAdobeFlashMediaServer™.OnewaytofeeddatatoFlashMediaServer(andthusontoFlashPlayerclients)isfromfilesintheFLVfileformat.StartingwithSWFfilespublishedforFlashPlayer7,FlashPlayercanalsoplayFLVfilesdirectlywithMIMEtypevideo/x-flv.AnFLVfileencodessynchronizedaudioandvideostreams.TheaudioandvideodatawithinFLVfilesareencodedinthesamewayasaudioandvideowithinSWFfiles.ThisdocumentdescribesFLVversion1.FormoreinformationontheFLVformat,seeChapter1,“TheFLVFileFormat,”onpage3.TheF4VfileformatStartingwithSWFfilespublishedforFlashPlayer9Update3(9,0,115,0),FlashPlayercanplayF4Vfiles.TheF4VformatisbasedontheformatspecifiedbyISO/IEC14496-12:ISObasemediafileformat.FormoreinformationontheF4Vformat,seeChapter2,“TheF4VFileFormat,”onpage15.AlargepartoftheF4Vformatinvolvesmetadata.FormoreinformationonF4Vmetadata,seeChapter3,“F4VMetadata,”onpage33.2Introduction31CHAPTER1TheFLVFileFormatEachtagtypeinanFLVfileconstitutesasinglestream.Therecanbenomorethanoneaudioandonevideostream,synchronizedtogether,inanFLVfile.Youcannotdefinemultipleindependentstreamsofasingletype.UnlikeSWFfiles,FLVfilesstoremultibyteintegersinbig-endianbyteorder.Forexample,asaUI16inSWFfileformat,thebytesequencethatrepresentsthenumber300(0x12C)is0x2C0x01;asaUI16inFLVfileformat,thebytesequencethatrepresentsthenumber300is0x010x2C.Also,FLVfilesusea3-byteintegertype,UI24,thatisnotusedinSWFfiles.4TheFLVFileFormatTheFLVheaderAllFLVfilesbeginwiththefollowingheader:TheDataOffsetfieldusuallyhasavalueof9forFLVversion1.Thisfieldispresenttoaccommodatelargerheadersinfutureversions.TheFLVfilebodyAftertheFLVheader,theremainderofanFLVfileconsistsofalternatingback-pointersandtags.Theyinterleaveasshowninthefollowingtable:FLVheaderFieldTypeCommentSignatureUI8Signaturebytealways'F'(0x46)SignatureUI8Signaturebytealways'L'(0x4C)SignatureUI8Signaturebytealways'V'(0x56)VersionUI8Fileversion(forexample,0x01forFLVversion1)TypeFlagsReservedUB[5]Mustbe0TypeFlagsAudioUB[1]AudiotagsarepresentTypeFlagsReservedUB[1]Mustbe0TypeFlagsVideoUB[1]VideotagsarepresentDataOffsetUI32Offsetinbytesfromstartoffiletostartofbody(thatis,sizeofheader)FLVfilebodyFieldTypeCommentPreviousTagSize0UI32Always0Tag1FLVTAGFirsttagPreviousTagSize1UI32Sizeofprevioustag,includingitsheader.ForFLVversion1,thisvalueis11plustheDataSizeoftheprevioustag.Tag2FLVTAGSecondtag...FLVtags5FLVtagsFLVtagshavethefollowingformat:Inplayback,thetimesequencingofFLVtagsdependsontheFLVtimestampsonly.Anytimingmechanismsbuiltintothepayloaddataformatareignored.PreviousTagSizeN-1UI32Sizeofsecond-to-lasttagTagNFLVTAGLasttagPreviousTagSizeNUI32SizeoflasttagFLVTAGFieldTypeCommentTagTypeUI8Typeofthistag.Valuesare:8:audio9:video18:scriptdataallothers:reservedDataSizeUI24LengthofthedataintheDatafieldTimestampUI24Timeinmillisecondsatwhichthedatainthistagapplies.ThisvalueisrelativetothefirsttagintheFLVfile,whichalwayshasatimestampof0.TimestampExtendedUI8ExtensionoftheTimestampfieldtoformaUI32value.Thisfieldrepresentstheupper8bits,whilethepreviousTimestampfieldrepresentsthelower24bitsofthetimeinmilliseconds.StreamIDUI24Always0DataIfTagType=8AUDIODATAIfTagType=9VIDEODATAIfTagType=18SCRIPTDATAOBJECTBodyofthetagFLVfilebodyFieldTypeComment6TheFLVFileFormatAudiotagsAudiotagsaresimilartotheDefineSoundtagintheSWFfileformat.TheirpayloaddataisidenticalexceptfortheadditionalNellymoser8-kHzformat,whichisnotpermittedinSWF.(ForinformationontheSWFfileformat,seetheSWFFileFormatSpecificationatwww.adobe.com/go/swf_file_format.)Format3,linearPCM,storesrawPCMsamples.Ifthedatais8-bit,thesamplesareunsignedbytes.Ifthedatais16-bit,thesamplesarestoredaslittleendian,signednumbers.Ifthedataisstereo,leftandrightsamplesarestoredinterleaved:left-right-left-right-andsoon.AUDIODATAFieldTypeCommentSoundFormat(seenotesfollowingtable)UB[4]0=LinearPCM,platformendian1=ADPCM2=MP33=LinearPCM,littleendian4=Nellymoser16-kHzmono5=Nellymoser8-kHzmono6=Nellymoser7=G.711A-lawlogarithmicPCM8=G.711mu-lawlogarithmicPCM9=reserved10=AAC14=MP38-Khz15=Device-specificsoundFormatofSoundDataFormats7,8,14,and15arereservedforinternaluseFormat10(AAC)issupportedinFlashPlayer9,0,115,0andhigher.SoundRateUB[2]0=5.5-kHz1=11-kHz2=22-kHz3=44-kHzSamplingrateForAAC:always3SoundSizeUB[1]0=snd8Bit1=snd16BitSizeofeachsampleForAAC:always1SoundTypeUB[1]0=sndMono1=sndStereoMonoorstereosoundForNellymoser:always0ForAAC:always1SoundDataUI8[sizeofsounddata]ifSoundFormat==10AACAUDIODATAelseSounddata—variesbyformatAudiotags7Format0PCMisthesameasformat3PCM,exceptthatformat0stores16-bitPCMsamplesintheendianorderoftheplatformonwhichthefilewascreated.Forthisreason,format0isnotrecommendedforuse.Nellymoser8-kHzisaspecialcase—the8-kHzsamplingrateisnotsupportedinotherformats,andtheSoundRatebitscan’trepresentthisvalue.WhenNellymoser8-kHzmonoisspecifiedinSoundFormat,theSoundRateandSoundTypefieldsareignored.ForotherNellymosersamplingrates,specifythenormalNellymoserSoundFormatandusetheSoundRateandSoundTypefieldsasusual.AACAUDIODATATheAACformatissupportedinFlashPlayer9,0,115,0andhigher.TheAudioSpecificConfigisexplainedinISO14496-3.NotethatitisnotthesameasthecontentsoftheesdsboxfromanMP4/F4Vfile.Thisstructureismoredeeplyembedded.AACAUDIODATAFieldTypeCommentAACPacketTypeUI80:AACsequenceheader1:AACrawDataUI8[n]ifAACPacketType==0AudioSpecificConfigelseifAACPacketType==1RawAACframedata8TheFLVFileFormatVideotagsVideotagsaresimilartotheVideoFrametagintheSWFfileformat,andtheirpayloaddataisidentical.(ForinformationontheSWFfileformat,seetheSWFFileFormatSpecificationatwww.adobe.com/go/swf_file_format.)IfFrameType=5,insteadofavideopayload,themessagestreamcontainsaUI8withthefollowingmeaning:■0=Startofclient-sideseekingvideoframesequence■1=Endofclient-sideseekingvideoframesequenceVIDEODATAFieldTypeCommentFrameTypeUB[4]1:keyframe(forAVC,aseekableframe)2:interframe(forAVC,anon-seekableframe)3:disposableinterframe(H.263only)4:generatedkeyframe(reservedforserveruseonly)5:videoinfo/commandframeCodecIDUB[4]1:JPEG(currentlyunused)2:SorensonH.2633:Screenvideo4:On2VP65:On2VP6withalphachannel6:Screenvideoversion27:AVCVideoDataIfCodecID=2H263VIDEOPACKETIfCodecID=3SCREENVIDEOPACKETIfCodecID=4VP6FLVVIDEOPACKETIfCodecID=5VP6FLVALPHAVIDEOPACKETIfCodecID=6SCREENV2VIDEOPACKETifCodecID=7AVCVIDEOPACKETVideoframepayload(seenotefollowingtable)Datatags9AVCVIDEOPACKETAnAVCVIDEOPACKETcarriesapayloadofAVCvideodata.SeeISO14496-12,8.15.3foranexplanationofcompositiontimes.TheoffsetinanFLVfileisalwaysinmilliseconds.SeeISO14496-15,5.2.4.1forthedescriptionofAVCDecoderConfigurationRecord.ThiscontainsthesameinformationthatwouldbestoredinanavcCboxinanMP4/FLVfile.DatatagsDatatagsencapsulatesingle-methodinvocation,whichisusuallycalledonaNetStreamobjectinFlashPlayer.Datatagsareformedfromamethodnameandasetofarguments.AVCVIDEOPACKETFieldTypeCommentAVCPacketTypeUI80:AVCsequenceheader1:AVCNALU2:AVCendofsequence(lowerlevelNALUsequenceenderisnotrequiredorsupported)CompositionTimeUI24ifAVCPacketType==1Compositiontimeoffsetelse0DataUI8[n]ifAVCPacketType==0AVCDecoderConfigurationRecordelseifAVCPacketType==1OneormoreNALUs(canbeindividualslicesperFLVpackets;thatis,fullframesarenotstrictlyrequired)elseifAVCPacketType==2EmptySCRIPTDATAFieldTypeCommentObjectsSCRIPTDATAOBJECT[]ArbitrarynumberofSCRIPTDATAOBJECTstructuresEndUI24Always9,alsoknownasaSCRIPTDATAOBJECTEND10TheFLVFileFormatSCRIPTDATAOBJECTandSCRIPTDATAOBJECTENDASCRIPTDATAOBJECTrecorddefinesobjectdatainActionScript™.ListsofSCRIPTDATAOBJECTrecordsareterminatedbyusingtheSCRIPTDATAOBJECTENDtag.SCRIPTDATAOBJECTFieldTypeCommentObjectNameSCRIPTDATASTRINGNameoftheobjectObjectDataSCRIPTDATAVALUEDataoftheobjectSCRIPTDATAOBJECTENDFieldTypeCommentObjectEndMarker2UI24Always9Datatags11SCRIPTDATASTRINGandSCRIPTDATALONGSTRINGTheSCRIPTDATASTRINGandSCRIPTDATALONGSTRINGrecordsareusedtodefinestringsfordatatags.TheSCRIPTDATALONGSTRINGrecordcanbeusedtospecifystringslargerthan65535characters.SCRIPTDATAVALUEASCRIPTDATAVALUErecordrepresentsanabstractdefinitionofanActionScriptvalueorobject.Itcancontainalistofvalues,objects,variables,orarrays.SCRIPTDATASTRINGFieldTypeCommentStringLengthUI16StringlengthinbytesStringDataSTRINGStringdataSCRIPTDATALONGSTRINGFieldTypeCommentStringLengthUI32StringlengthinbytesStringDataSTRINGStringdataSCRIPTDATAVALUEFieldTypeCommentType(seenotesfollowingtable)UI8Typeofthevariable:0=Numbertype1=Booleantype2=Stringtype3=Objecttype4=MovieCliptype5=Nulltype6=Undefinedtype7=Referencetype8=ECMAarraytype10=Strictarraytype11=Datetype12=LongstringtypeECMAArrayLengthIfType=8,UI32ApproximatenumberoffieldsofECMAarray12TheFLVFileFormatIfType=8(ECMAarraytype),theECMAArrayLengthprovidesahinttothesoftwareabouthowmanyitemsmightbeinthearray.ThearraycontinuesuntilSCRIPTDATAVARIABLEENDappears.IfType=10(strictarraytype),thearraybeginswithaUI32typeandcontainsthatexactnumberofitems.ThearraydoesnotterminatewithaSCRIPTDATAVARIABLEENDtag.SCRIPTDATAVARIABLEandSCRIPTDATAVARIABLEENDASCRIPTDATAVARIABLErecorddefinesvariabledatainActionScript.ListsofSCRIPTDATAVARIABLErecordsareterminatedbyusingtheSCRIPTDATAVARIABLEENDtag.ScriptDataValueIfType=0,DOUBLEIfType=1,UI8IfType=2,SCRIPTDATASTRINGIfType=3,SCRIPTDATAOBJECT[n]IfType=4,SCRIPTDATASTRINGdefiningtheMovieClippathIfType=7,UI16IfType=8,SCRIPTDATAVARIABLE[ECMAArrayLength]IfType=10,SCRIPTDATAVARIABLE[n]IfType=11,SCRIPTDATADATEIfType=12,SCRIPTDATALONGSTRINGScriptdatavaluesScriptDataValueTerminatorIfType=3,SCRIPTDATAOBJECTENDIfType=8,SCRIPTDATAVARIABLEENDTerminatorsforObjectandStrictarraylistsSCRIPTDATAVARIABLEFieldTypeCommentVariableNameSCRIPTDATASTRINGNameofthevariableVariableDataSCRIPTDATAVALUEDataofthevariableSCRIPTDATAVALUEFieldTypeCommentonMetaData13SCRIPTDATADATEASCRIPTDATADATErecorddefinesaparticulardateandtime.onMetaDataAnFLVfilecancontainmetadatawithan“onMetaData”marker.VariousstreampropertiesareavailabletoarunningActionScriptprogramviatheNetStream.onMetaDataproperty.Theavailablepropertiesdifferdependingonthesoftwareused.Commonpropertiesinclude:■duration:aDOUBLEindicatingthetotaldurationofthefileinseconds■width:aDOUBLEindicatingthewidthofthevideoinpixels■height:aDOUBLEindicatingtheheightofthevideoinpixels■videodatarate:aDOUBLEindicatingthevideobitrateinkilobitspersecond■framerate:aDOUBLEindicatingthenumberofframespersecond■videocodecid:aDOUBLEindicatingthevideocodecIDusedinthefile(see“Videotags”onpage8foravailableCodecIDvalues)■audiosamplerate:aDOUBLEindicatingthefrequencyatwhichtheaudiostreamisreplayed■audiosamplesize:aDOUBLEindicatingtheresolutionofasingleaudiosample■stereo:aBOOLindicatingwhetherthedataisstereo■audiocodecid:aDOUBLEindicatingtheaudiocodecIDusedinthefile(see“Audiotags”onpage6foravailableSoundFormatvalues)■filesize:aDOUBLEindicatingthetotalsizeofthefileinbytesSCRIPTDATAVARIABLEENDFieldTypeCommentVariableEndMarker1UI24Always9SCRIPTDATADATEFieldTypeCommentDateTimeDOUBLENumberofmillisecondssinceJan1,1970UTC.LocalDateTimeOffsetSI16LocaltimeoffsetinminutesfromUTC.FortimezoneslocatedwestofGreenwich,UK,thisvalueisanegativenumber.TimezoneseastofGreenwich,UK,arepositive.14TheFLVFileFormat152CHAPTER2TheF4VFileFormatFlashPlayerUpdate3(9,0,115,0)andhighercanplayF4Vfiles.TheF4VformatisbasedontheformatspecifiedbyISO/IEC14496-12:ISObasemediafileformat.UnlikeSWFfiles,F4Vfilesstoremultibyteintegersinbig-endianbyteorder.Forexample,asaUI16inSWFfileformat,thebytesequencethatrepresentsthenumber300(0x12C)is0x2C0x01;asaUI16inF4Vfileformat,thebytesequencethatrepresentsthenumber300is0x010x2C.ThischapterdiscussesallaspectsoftheF4Vformatexceptmetadata.Forinformationonmetadata,seeChapter3,“F4VMetadata,”onpage33.TheF4VboxThefundamentalbuildingblockofanF4VfileisaboxwhichhasthefollowingBOXformat:EachboxstructurebeginswithaBOXHEADERstructure:F4VboxFieldTypeCommentHeaderBOXHEADERAconsistentheaderthatallboxeshavePayloadUI8[]Anumberofbytes,thelengthofwhichisdefinedbytheBOXHEADERBOXHEADERFieldTypeCommentTotalSizeUI32Thetotalsizeoftheboxinbytes,includingthisheaderBoxTypeUI32ThetypeofatomExtendedSizeIfTotalSizeequals1UI64Thetotal64-bitlengthoftheboxinbytes,includingthisheader16TheF4VFileFormatManyboxesarewellunder4gigabytesinlengthandcanstoretheirsizeintheTotalSizefield.Theformatalsosupportsverylargeboxesbysettingthe32-bitTotalSizefieldto1andstoringa64-bitsizeinExtendedSize.Eachboxisidentifiedwitha32-bittype.Formostboxes,this32-bittypedoublesasahuman-readablefour-characterASCIIcodeorFourCC,suchas'moov'(0x6D6F6F76)and'mdat'(0x6D646174).Theboxpayloadimmediatelyfollowstheboxheader.Thesizeofthepayloadinbytesisequaltothetotalsizeoftheboxminuseither8bytesor16bytes,dependingonthesizeoftheheader.Formoreinformation,seesection4.2ofISO/IEC14496-12.ftypboxTheF4VformatisbasedontheISOMP4format,whichinturnisbasedontheAppleQuickTimecontainerformat.Thesubsetsoftheformatsupportdifferentfeatures.Theftypboxhelpsidentifythefeaturesthataprogrammustsupporttoplayaparticularfile.FlashPlayerdoesnotenforceanyrestrictionswithrespecttoftypboxes.Theprogramtriestoplayanyfileitisgiven,withintherestrictionsofthecodectypesitsupports.Formoreinformation,seesection4.3ofISO/IEC14496-12.ftypboxFieldTypeCommentsHeaderBOXHEADERBoxType='ftyp'(0x66747970)MajorBrandUI32TheprimarybrandidentifierMinorVersionUI32ThesecondarybrandidentifierCompatibleBrandsUI32[]Arbitrarynumberofcompatiblebrands,untiltheendoftheboxmvhdbox17moovboxAnF4Vfilemustcontainoneandonlyonemoovbox.Themoovboxiseffectivelythe“header”ofanF4Vfile.Themoovboxitselfcontainsoneormoreotherboxes,whichinturncontainotherboxeswhichdefinethestructureoftheF4Vdata.Formoreinformation,seesection8.1ofISO/IEC14496-12.mvhdboxAnF4Vfilemustcontainoneandonlyonemvhdbox.ThemvhdboxiscontainedwithinamoovboxanddefinesplaybackinformationthatappliestotheentireF4Vfile.moovboxFieldTypeCommentHeaderBOXHEADERBoxType='moov'(0x6D6F6F76)BoxesBOX[]ManyotherboxeswhichdefinethestructuremvhdboxFieldTypeCommentHeaderBOXHEADERBoxType='mvhd'(0x6D766864)VersionUI8Either0or1FlagsUI24Reserved,setto0CreationTime