Quicktime File Format (2012-08-14).pdf

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Profile Atom GuidelinesUniversal FeaturesFeature Value AlgorithmConsult the audio sample descriptions.Reader ResponsibilitiesThe reader should be prepared to either play the specified number of channels or to map the audio to thenumber of channels the reader supports (for example, mixing down stereo sound for a monaural speaker).2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.420
Audio Priming - Handling Encoder Delay in AACThis appendix describes temporal positioning of a source audio signal after AAC encoding into a sound trackfor QuickTime media files. The mechanisms described here are specified in ISO MPEG-4 standards (ISO/IEC14496-12, 2008) and are used here with additional constraints.Note on language useAAC implementations typically represent 1024 PCM audio samples in one AAC packet (synonymousin this context with a QuickTime media sample, and also referred to in ISO documents as an “accessunit”). The terms “sample” and “audio sample” in this appendix are used to refer to PCM samples.For the encoded audio data, the terms “AAC packet” and QuickTime “media sample” are used.Background – AAC EncodingAAC requires data beyond the source PCM audio samples in order to correctly encode and decode audiosamples due to the nature of the encoding algorithm. AAC encoding uses a transform over consecutive setsof 2048 audio samples, applied every 1024 audio samples (overlapped). For correct audio to be decoded, bothtransforms for any period of 1024 audio samples are needed. For this reason, encoders add at least 1024samples of silence before the first ‘true’ audio sample, and often add more. This is called variously “priming”,“priming samples”, or “encoder delay”. A couple of definitions for use in this discussion:●●Encoder delay is the delay incurred during encoding to produce properly formed, encoded audio packets.It typically refers to the number of silent media samples (priming samples) added to the front of an AACencoded bitstream.Decoder delay is the number of “pre-roll” audio samples required to reproduce an encoded source audiosignal for a given time index. For AAC this number is typically 1024 and is algorithmically based. This is incontrast to encoder delay which is determined by the encoder and encoding configuration used. However,decoder delay establishes the minimum encoder delay possible (that is, 1024 for AAC).The common practice is to propagate the encoder delay in the AAC bitstream. When these audio packets arethen decoded back to the PCM domain, the source waveform represented will be offset in its entirety by thisencoder delay amount. Since encoded audio packets hold a fixed number of audio samples (for instance, 1024samples) additional trailing or ‘remainder’ silent samples following the last source sample are required so asto pad the final audio packet to the required length.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.421
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QuickTime File FormatSpecification
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ContentsReference Movie Atom 120Ref
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ContentsSprite Track Property Atoms
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ContentsSome Useful Examples and Sc
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ContentsAudio Sample Rate for a Sam
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Figures, Tables, and ListingsFigure
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Figures, Tables, and ListingsFigure
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Figures, Tables, and ListingsTable
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Introduction to QuickTime File Form
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Overview of QTFFQuickTime movies ar
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Overview of QTFFAtomsAtom LayoutFig
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Overview of QTFFQT Atoms and Atom C
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Overview of QTFFQuickTime Movie Fil
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Movie AtomsOverview of Movie AtomsO
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Movie AtomsOverview of Movie AtomsN
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Movie AtomsOverview of Movie AtomsC
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Movie AtomsOverview of Movie AtomsF
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Movie AtomsOverview of Movie AtomsF
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Movie AtomsOverview of Movie AtomsA
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Movie AtomsTrack AtomsPrint to Vide
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Movie AtomsTrack AtomsNote Figure 2
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Movie AtomsTrack AtomsFigure 2-7 (p
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Movie AtomsTrack AtomsAlternate gro
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Movie AtomsTrack AtomsAlthough the
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Movie AtomsTrack AtomsRegion sizeTh
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Movie AtomsTrack AtomsNote If the e
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Movie AtomsTrack AtomsTrack Input M
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Movie AtomsTrack AtomsInput typeA 3
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Movie AtomsMedia AtomsMedia atoms c
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Movie AtomsMedia AtomsTime scaleA t
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Movie AtomsMedia AtomsHandler Refer
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Movie AtomsMedia AtomsNote “Using
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Movie AtomsMedia AtomsOpcolorThree
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Movie AtomsMedia AtomsMedia types t
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Movie AtomsMedia AtomsFlagsA 3-byte
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Movie AtomsMedia AtomsData referenc
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Movie AtomsSample AtomsSamples are
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Movie AtomsSample AtomsFigure 2-33
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Movie AtomsSample AtomsThe sample d
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Movie AtomsSample AtomsSizeA 32-bit
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Movie AtomsSample AtomsNote At the
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Movie AtomsSample AtomsSizeA 32-bit
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Movie AtomsSample AtomsVersionA 1-b
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Movie AtomsSample AtomsNote The sam
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Movie AtomsSample AtomsSample depen
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Movie AtomsCompressed Movie Resourc
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Movie AtomsReference MoviesApplicat
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Movie AtomsReference MoviesData ref
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Movie AtomsReference MoviesCPU Spee
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Movie AtomsReference MoviesFlagsA 3
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MetadataThis chapter describes how
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MetadataMetadata StructureFigure 3-
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MetadataExtensibilityTypeA 32-bit u
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MetadataLanguage List AtomField Siz
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MetadataMetadata Item Keys AtomThis
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MetadataMetadata Item AtomFigure 3-
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MetadataLocale IndicatorValueotherw
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MetadataData Atom StructureNameAn a
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MetadataLocation MetadataLocation M
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MetadataQuickTime Metadata KeysKeyK
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Media Data Atom TypesQuickTime uses
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Media Data Atom TypesVideo MediaCom
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Media Data Atom TypesVideo MediaCol
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Media Data Atom TypesVideo MediaDes
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Media Data Atom TypesVideo MediaThe
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Media Data Atom TypesVideo MediaSch
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Media Data Atom TypesVideo MediaTab
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Media Data Atom TypesVideo MediaNot
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Media Data Atom TypesSound MediaSou
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Media Data Atom TypesSound MediaThe
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Media Data Atom TypesSound Mediaaud
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Media Data Atom TypesSound MediaTyp
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Media Data Atom TypesSound MediaThe
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Media Data Atom TypesTimecode Media
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Media Data Atom TypesTimecode Media
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Media Data Atom TypesText MediaDisp
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Media Data Atom TypesText MediaFore
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Media Data Atom TypesClosed Caption
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Media Data Atom TypesSubtitle Media
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Media Data Atom TypesMusic Media●
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Media Data Atom TypesSprite MediaSp
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Media Data Atom TypesSprite Track P
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Media Data Atom TypesSprite Track M
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Media Data Atom TypesSprite Track M
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Media Data Atom TypesSprite Media A
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Media Data Atom TypesSprite Media A
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Media Data Atom TypesSprite Button
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Media Data Atom TypesSprite Media H
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Media Data Atom TypesWired Action G
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Media Data Atom TypesFlash MediakAc
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Media Data Atom TypesTween MediaTwe
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Media Data Atom TypesTween Media●
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Media Data Atom TypesTween MediakTw
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Media Data Atom TypesTween MediaTwe
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Media Data Atom TypesTrack Referenc
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Media Data Atom TypesStreaming Medi
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Media Data Atom TypesHint Media●
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Media Data Atom TypesHint MediaMovi
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Media Data Atom TypesHint Sample Da
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Media Data Atom TypesHint Sample Da
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Media Data Atom TypesPacketization
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Media Data Atom TypesVR Media} QTVR
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Media Data Atom TypesVR MediaUInt32
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Media Data Atom TypesVR Mediareserv
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Media Data Atom TypesCustom Cursor
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Media Data Atom TypesNode Informati
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Media Data Atom TypesQuickTime VR F
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Media Data Atom TypesQuickTime VR F
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Media Data Atom TypesQTVR TrackImpo
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Media Data Atom TypesPanorama Track
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Media Data Atom TypesCubic Panorama
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Media Data Atom TypesHot Spot Image
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Media Data Atom TypesObject TracksT
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Media Data Atom TypesObject Tracksd
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Media Data Atom TypesObject Tracksk
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Media Data Atom TypesMovie MediaFor
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Media Data Atom TypesMovie MediaNot
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Media Data Atom TypesMovie MediakMo
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Basic Data TypesThis chapter descri
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Basic Data TypesLanguage Code Value
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Basic Data TypesCalendar Date and T
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Basic Data TypesRGB ColorsTable 5-3
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Some Useful Examples and ScenariosT
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Some Useful Examples and ScenariosO
Page 370 and 371: QuickTime Image File FormatNote The
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Page 394 and 395: Profile Atom GuidelinesProfile Atom
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Page 436 and 437: GlossaryAAC Advanced Audio Coding (
Page 438 and 439: Glossaryfile preview A thumbnail pi
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Page 446: Apple Inc.© 2004, 2012 Apple Inc.A
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