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

Profile Atom GuidelinesUniversal FeaturesFeature ValuesThe feature value holds one of the following two values: 0 if the audio is constant bit rate, or 1 if the audio isvariable bit rate.Writer ResponsibilitiesA writer of the Audio Variable Bit Rate Indication feature should determine if the audio frames are constant orvariable bit rate in nature and record either 0 or 1, respectively.Feature Value AlgorithmConsult the audio sample descriptions. If the compressionID field in the sample descriptions is 0 or -1, thenthe audio is constant bit rate. If the field is -2, then the same algorithm as for video applies: if all the sampleshave both constant duration and constant size, then the audio is constant bit rate; otherwise it is variable.Reader ResponsibilitiesA reader of this feature code should only expect the values 0 or 1.Audio Channel CountContaining profile atomTrack (sound), moviepart-ID0x20202020 (universal feature)feature-code'achc'feature-valueUnsigned int(32) holding the number of audio channelsFeature ValuesThe feature value is an unsigned 32-bit integer holding the number of audio channels encoded by a SoundTrack in the movie. For monaural, the value would be 1. For stereo, the value would be 2. Note that the audiochannel count is a standard field in the sound sample description.Writer ResponsibilitiesA writer of the Audio Channel Count feature should determine the number of audio channels encoded in thesound track or tracks of the movie.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.419