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

Profile Atom GuidelinesUniversal Featurespart-ID0x20202020 (universal feature)feature-code'mp4a'feature-valueUnsigned int(32) where least significant 5 bits hold the AudioObjectType as found in theAudioSpecificInfo (as defined in specification ISO/IEC 14496-3, subclause 1.6) found in the esds ofthe MPEG-4 audio codec (QuickTime type 'mp4a') sample descriptionFeature ValuesThe least significant 5 bits hold the value. The most significant 27 bits of the feature value should be set to 0.The list of audio object type constants is defined in specification ISO/IEC 14496-3, subclause 1.5.1.1.Examples: AAC LC is indicated by the value 2, CELP is indicated by the value 8.Writer ResponsibilitiesA writer of the MPEG-4 Audio Codec feature should record the 5 bits corresponding to the AudioObjectTypefound in the ES_descriptor's audio DecoderSpecificConfig. The most significant 27 bits of the valueshould be set to 0.Note A writer that records the MPEG-4 Audio Codec feature is encouraged also to write the QuickTimeAudio Codec Type feature.Feature Value AlgorithmThe MPEG-4 audio codec value is the 5 bits of the AudioObjectType found in the AudioSpecificInfo (aDecoderSpecificInfo). See specification ISO/IEC 14496, subclause 1.6. The AudioSpecificInfo is foundin the MPEG-4 Elementary Stream Descriptor Atom within the siDecompressionParam atom of the audiosample description for the QuickTime audio codec of type 'mp4a'.Reader ResponsibilitiesA reader of this feature code should compare the recorded value with the set of MPEG-4 audio decoderssupported by the reader.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.410