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

Media Data Atom TypesSound MediaSound Sample Description (Version 2)QuickTime 7 introduced a new version of the sound sample description, version 2, which extends QuickTimecapabilities to include high resolution audio with another expansion of the sound sample description structure.In QuickTime 7, the sound and audio facilities are based on the Core Audio framework facilities and the SoundManager has been deprecated. In this version of the sound sample description, the format field is set to ‘lpcm’for uncompressed data. For compressed data formats, the format field is set to the compression type code(normally ‘mp4a’) and the compression specifics and other features of QuickTime 7 are supplied by extensions.The version field is set to 2 for this version of the sound sample description structure.The sound sample description v2 structure adds the following new fields, appending to the v1 structure andrenaming the four fields added in v1 to help ensure backwards compatibility with older applications. Theversion 2 fields are:Important The values contained in these fields have different meanings for compressed and uncompressedaudio. The meaning may not be easily deducible from the field name and require reference to the appropriatesound sample description extensions to understand fully.VersionA 16-bit integer that holds the sample description version (set to 2).Revision levelA 16-bit integer that must be set to 0.VendorA 32-bit integer that must be set to 0.always3A 16-bit integer field that must be set to 3.always16A 16-bit integer field that must be set to 16 (0x0010).alwaysMinus2A 16-bit integer field that must be set to -2 (0xFFFE).always0A 16-bit integer field that must be set to 0.always65536A 32-bit integer field that must be set to 65536.sizeOfStructOnlyA 32-bit integer field providing the offset to sound sample description structure’s extensions.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.181