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

Profile Atom GuidelinesUniversal FeaturesExamples: 24 kHz = 24000, 44.1 kHz = 44100.Writer ResponsibilitiesA writer of the Audio Sample Rate feature should record the integer portion (rounded up if there is a fractionalportion) of the audio sample rate found in a sound track’s SoundDescription structure.If multiple audio sample rates are used in the movie, then either all must recorded in the profile atom, or nonemust be recorded.Feature Value AlgorithmThis is the integer portion of the sample rate from a QuickTime audio sample description (rounded up if thereis a fractional portion). If the sample rate is greater than 64 kHz, the integer portion can be recorded here.If a sample rate has a fractional portion, the writer should round up to the nearest integer. So, the 22254.54545value that may occur in QuickTime audio as a Fixed value represented as 0x56EE8BA3 can be recorded as22255.Reader ResponsibilitiesA reader of this feature code should compare the recorded value with its own audio sample rate limits. If thereader only supports discrete values (such as 44100), it can perform equality comparisons (=). If the readersupports ranges of audio sample rates (such as all rates less than or equal to 32000), the reader can performrelative comparisons (=).Audio Variable Bit Rate IndicationContaining profile atomTrack (sound), moviepart-ID0x20202020 (universal feature)feature-code'avbr'feature-valueUnsigned int(32) holding the value 0 if the audio is constant bit rate or 1 if the audio is variable bitrate2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.418