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

Audio Priming - Handling Encoder Delay in AACUsing Track Structures to Represent Encoder Delay ExplicitlyThe sample group description atom contains the following data elements:SizeA 32-bit integer that specifies the number of bytes in this sample group description atom.TypeA 32-bit integer that identifies the atom type, set to 'sgpd'.VersionA 1-byte specification of the version of this sample group description, set to 1.FlagsA 3-byte reserved space, set to 0Grouping typeA 32-bit integer that identifies the grouping type of this sample group description, set to ‘roll’.Default lengthA 32-bit integer indicating the length of the group entry in the payload data, set to 2 (bytes).Entry countA 32-bit integer giving the number of entries in the payload data field, set to 1.Payload dataA 16-bit signed integer giving the roll distance, set to -1 value for AAC audio.Sample-To-Group AtomsSample-to-group atoms are used to find the group that a sample belongs to and the associated descriptionof that sample group. The sample-to-group atom has an atom type of ‘sbgp’.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.427