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

Audio Priming - Handling Encoder Delay in AACExample—Representing Encoder Delay ExplicitlySizeA 32-bit integer that specifies the number of bytes in this sample-to-group atom.TypeA 32-bit integer that identifies the atom type; set to 'sbgp'.VersionA 1-byte specification of the version of this sample-to-group atom, set to 0FlagsA 3-byte reserved space, set to 0.Grouping typeA 32-bit integer identifying the grouping type, set to ‘roll’.Entry countA 32-bit integer giving the number of entries in the table table data that follows.Table dataA table of sample count and group description index pairs as shown in Figure G-4 (page 429).Figure G-4The layout of the table data formatSample countGroup description IndexField4 4BytesSample countA 32-bit integer that provides the number of consecutive media samples with the same samplegroup descriptor. The value is typically the same as in the sample size atom’s number of entriesfield.Group description indexA 32-bit integer the value of which is the index into the sample group description atom’s payloaddata table which describes the samples in this group. The index ranges from 1 to the number ofpayload data entries in the sample group description atom, or takes the value 0 to indicate thatthis group of samples is a member of no group of this type.Example—Representing Encoder Delay ExplicitlyConsider the following example of a typical case of PCM source sound data to be encoded as AAC:2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.429