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

Media Data Atom TypesSound MediaAudio channel layoutA big-endian AudioChannelLayout structure as defined in CoreAudioTypes.h. See the OS X DeveloperLibrary for CoreAudio framework details.Subtitle Follows Track Reference AtomSound tracks can have a track reference of type 'folw' (for “follows”) to a single subtitle track from amongthe subtitle tracks in the same alternate group; this subtitle track should be considered the default to select ifthe sound track is selected. Use this only if compatibility between language tags is not possible for some reasonmaking it impossible to otherwise select a default track. See “Preparing Sound and Subtitle Alternate Groupsfor Use with Apple Devices” (page 334) for related information.Sound Sample DataThe format of data stored in sound samples is completely dependent on the type of the compressed datastored in the sound sample description. The following sections discuss some of the formats supported byQuickTime.Uncompressed 8-Bit SoundEight-bit audio is stored in offset-binary encodings. If the data is in stereo, the left and right channels areinterleaved.Uncompressed 16-Bit SoundSixteen-bit audio may be stored in two’s-complement encodings. If the data is in stereo, the left and rightchannels are interleaved.IMA, uLaw, and aLaw●IMA 4:1The IMA encoding scheme is based on a standard developed by the International Multimedia Associationfor pulse code modulation (PCM) audio compression. QuickTime uses a slight variation of the format toallow for random access. IMA is a 16-bit audio format which supports 4:1 compression. It is defined asfollows:kIMACompression = FOUR_CHAR_CODE('ima4'), /*IMA 4:1*/●uLaw 2:1 and aLaw 2:12012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.187