rfc3533oggWord文件下载.docx

rfc3533oggWord文件下载.docx

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Thekeywords"

MUST"

"

MUSTNOT"

REQUIRED"

SHALL"

SHALLNOT"

"

SHOULD"

SHOULDNOT"

RECOMMENDED"

MAY"

and"

OPTIONAL"

inthis

documentaretobeinterpretedasdescribedinBCP14,RFC2119[2].

TableofContents

1.Introduction.........................2

2.Definitions.........................2

3.Requirementsforagenericencapsulationformat.......3

4.TheOggbitstreamformat...................3

5.Theencapsulationprocess..................6

6.TheOggpageformat.....................9

7.SecurityConsiderations...................11

8.References..........................12

A.Glossaryoftermsandabbreviations.............13

B.Acknowledgements.......................14

Author'

sAddress.......................14

FullCopyrightStatement...................15

PfeifferInformational[Page1]

RFC3533OGGMay2003

1.Introduction

TheOggbitstreamformathasbeendevelopedasapartofalarger

projectaimedatcreatingasetofcomponentsforthecodingand

decodingofmultimediacontent（codecs）whicharetobefreely

availableandfreelyre-implementable,bothinsoftwareandin

hardwareforthecomputingcommunityatlarge,includingtheInternet

community.ItistheintentionoftheOggdevelopersrepresentedby

Xiph.Orgthatitbeusablewithoutintellectualpropertyconcerns.

ThisdocumentdescribestheOggbitstreamformatandhowtouseitto

encapsulateoneorseveralmediabitstreamscreatedbyoneorseveral

encoders.TheOggtransportbitstreamisdesignedtoprovide

framing,errorprotectionandseekingstructureforhigher-level

codecstreamsthatconsistofraw,unencapsulateddatapackets,such

astheVorbisaudiocodecortheupcomingTarkinandTheoravideo

codecs.Itiscapableofinterleavingdifferentbinarymediaand

othertime-continuousdatastreamsthatarepreparedbyanencoderas

asequenceofdatapackets.Oggprovidesenoughinformationto

properlyseparatedatabackintosuchencodercreateddatapacketsat

theoriginalpacketboundarieswithoutrelyingondecodingtofind

packetboundaries.

PleasenotethattheMIMEtypeapplication/ogghasbeenregistered

withtheIANA[1].

2.Definitions

FordescribingtheOggencapsulationprocess,asetoftermswillbe

usedwhosemeaningneedstobewellunderstood.Therefore,someof

themostfundamentaltermsaredefinednowbeforewestartwiththe

descriptionoftherequirementsforagenericmediastream

encapsulationformat,theprocessofencapsulation,andtheconcrete

formatoftheOggbitstream.SeetheAppendixforamorecomplete

glossary.

TheresultofanOggencapsulationiscalledthe"

Physical（Ogg）

Bitstream"

.Itencapsulatesoneorseveralencoder-created

bitstreams,whicharecalled"

LogicalBitstreams"

.Alogical

bitstream,providedtotheOggencapsulationprocess,hasa

structure,i.e.,itissplitupintoasequenceofso-called

Packets"

.Thepacketsarecreatedbytheencoderofthatlogical

bitstreamandrepresentmeaningfulentitiesforthatencoderonly

（e.g.,anuncompressedstreammayusevideoframesaspackets）.They

donotcontainboundaryinformation-strungtogethertheyappearto

bestreamsofrandombyteswithnolandmarks.

PfeifferInformational[Page2]

RFC3533OGGMay2003

Pleasenotethattheterm"

packet"

isnotusedinthisdocumentto

signifyentitiesfortransportoveranetwork.

3.Requirementsforagenericencapsulationformat

ThedesignideabehindOggwastoprovideageneric,linearmedia

transportformattoenablebothfile-basedstorageandstream-based

transmissionofoneorseveralinterleavedmediastreamsindependent

oftheencodingformatofthemediadata.Suchanencapsulation

formatneedstoprovide:

oframingforlogicalbitstreams.

ointerleavingofdifferentlogicalbitstreams.

odetectionofcorruption.

orecaptureafteraparsingerror.

opositionlandmarksfordirectrandomaccessofarbitrarypositions

inthebitstream.

ostreamingcapability（i.e.,noseekingisneededtobuilda100%

completebitstream）.

osmalloverhead（i.e.,usenomorethanapproximately1-2%of

bitstreambandwidthforpacketboundarymarking,high-level

framing,syncandseeking）.

osimplicitytoenablefastparsing.

osimpleconcatenationmechanismofseveralphysicalbitstreams.

Allofthesedesignconsiderationshavebeentakenintoconsideration

forOgg.Oggsupportsframingandinterleavingoflogical

bitstreams,seekinglandmarks,detectionofcorruption,andstream

resynchronisationafteraparsingerrorwithnomorethan

approximately1-2%overhead.Itisagenericframeworktoperform

encapsulationoftime-continuousbitstreams.Itdoesnotknowany

specificsaboutthecodecdatathatitencapsulatesandisthus

independentofanymediacodec.

4.TheOggbitstreamformat

AphysicalOggbitstreamconsistsofmultiplelogicalbitstreams

interleavedinso-called"

Pages"

.Wholepagesaretakeninorder

frommultiplelogicalbitstreamsmultiplexedatthepagelevel.The

logicalbitstreamsareidentifiedbyauniqueserialnumberinthe

PfeifferInformational[Page3]

headerofeachpageofthephysicalbitstream.Thisuniqueserial

numberiscreatedrandomlyanddoesnothaveanyconnectiontothe

contentorencoderofthelogicalbitstreamitrepresents.Pagesof

alllogicalbitstreamsareconcurrentlyinterleaved,buttheyneed

notbeinaregularorder-theyareonlyrequiredtobeconsecutive

withinthelogicalbitstream.Oggdemultiplexingreconstructsthe

originallogicalbitstreamsfromthephysicalbitstreambytakingthe

pagesinorderfromthephysicalbitstreamandredirectingtheminto

theappropriatelogicaldecodingentity.

EachOggpagecontainsonlyonetypeofdataasitbelongstoone

logicalbitstreamonly.Pagesareofvariablesizeandhaveapage

headercontainingencapsulationanderrorrecoveryinformation.Each

logicalbitstreaminaphysicalOggbitstreamstartswithaspecial

startpage（bos=beginningofstream）andendswithaspecialpage

（eos=endofstream）.

Thebospagecontainsinformationtouniquelyidentifythecodectype

andMAYcontaininformationtosetupthedecodingprocess.Thebos

pageSHOULDalsocontaininformationabouttheencodedmedia-for

example,foraudio,itshouldcontainthesamplerateandnumberof

channels.Byconvention,thefirstbytesofthebospagecontain

magicdatathatuniquelyidentifiestherequiredcodec.Itisthe

responsibilityofanyonefieldinganewcodectomakesureitis

possibletoreliablydistinguishhis/hercodecfromallothercodecs

inuse.Thereisnofixedwaytodetecttheendofthecodec-

identifyingmarker.Theformatofthebospageisdependentonthe

codecandthereforeMUSTbegivenintheencapsulationspecification

ofthatlogicalbitstreamtype.Oggalsoallowsbutdoesnotrequire

secondaryheaderpacketsafterthebospageforlogicalbitstreams

andthesemustalsoprecedeanydatapacketsinanylogical

bitstream.Thesesubsequentheaderpacketsareframedintoan

integralnumberofpages,whichwillnotcontainanydatapackets.

So,aphysicalbitstreambeginswiththebospagesofalllogical

bitstreamscontainingoneinitialheaderpacketperpage,followedby

thesubsidiaryheaderpacketsofallstreams,followedbypages

containingdatapackets.

Theencapsulationspecificationforoneormorelogicalbitstreamsis

calleda"

mediamapping"

.Anexampleforamediamappingis"

Ogg

Vorbis"

whichusestheOggframeworktoencapsulateVorbis-encoded

audiodataforstream-basedstorage（suchasfiles）andtransport

（suchasTCPstreamsorpipes）.OggVorbisprovidesthenameand

revisionoftheVorbiscodec,theaudiorateandtheaudioqualityon

theOggVorbisbospage.Italsousestwoadditionalheaderpages

perlogicalbitstream.TheOggVorbisbospagestartswiththebyte

0x01,followedby"

vorbis"

（atotalof7bytesofidentifier）.

PfeifferInformational[Page4]

Oggknowstwotypesofmultiplexing:

concurrentmultiplexing（so-

called"

Grouping"

）andsequentialmultiplexing（so-called

Chaining"

）.Groupingdefineshowtointerleaveseverallogical

bitstreamspage-wiseinthesamephysicalbitstream.Groupingisfor

exampleneededforinterleavingavideostreamwithseveral

synchronisedaudiotracksusingdifferentcodecsindifferentlogical

bitstreams.Chainingontheotherhand,isdefinedtoprovidea

simplemechanismtoconcatenatephysicalOggbitstreams,asisoften

neededforstreamingapplications.

Ingrouping,allbospagesofalllogicalbitstreamsMUSTappear

togetheratthebeginningoftheOggbitstream.Themediamapping

specifi