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

Audio Priming - Handling Encoder Delay in AACExample—Representing Encoder Delay ExplicitlyEntry count: 1Number of entries: 1with this table data:Track duration: 240000 (source duration)Media time: 2112 (accounts for the encoder delay)Media rate: 1.0Note For this example, the conventional encoder delay value of 2112 audio samples has been used.Alternative encoder delay values can also be explicitly represented with this mechanism, dependingupon codec implementation.The sample group description atom contains this data:Size: 26Type: ‘sgpd’Version: 1Flags: 0Grouping type: ‘roll’Default length: 2Entry count: 1with this table data:payload data: -1Note Recall that the payload data value could be an alternative value, depending upon the particularcodec in use. -1 is typical for current AAC codecs.And the sample-to-group atom contains this data:Size: 22Type: ‘sbgp’Version: 0Flags: 02012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.431