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

Movie AtomsSample AtomsThe sample description atom has an atom type of 'stsd'. The sample description atom contains a table ofsample descriptions. A media may have one or more sample descriptions, depending upon the number ofdifferent encoding schemes used in the media and on the number of files used to store the data. Thesample-to-chunk atom identifies the sample description for each sample in the media by specifying the indexinto this table for the appropriate description (see “Sample-to-Chunk Atoms” (page 109)).The sample description atom contains the following data elements.SizeA 32-bit integer that specifies the number of bytes in this sample description atom.TypeA 32-bit integer that identifies the atom type; this field must be set to 'stsd'.VersionA 1-byte specification of the version of this sample description atom.FlagsA 3-byte space for sample description flags. Set this field to 0.Number of entriesA 32-bit integer containing the number of sample descriptions that follow.Sample description tableAn array of sample descriptions. For details, see “General Structure of a Sample Description” (page 100).General Structure of a Sample DescriptionWhile the exact format of the sample description varies by media type, the first four fields of every sampledescription are the same.Sample description sizeA 32-bit integer indicating the number of bytes in the sample description.Important When parsing sample descriptions in the ‘stsd’ atom, be aware of the sample descriptionsize value in order to read each table entry correctly. Some sample descriptions terminate with four zerobytes that are not otherwise indicated.Data formatA 32-bit integer indicating the format of the stored data. This depends on the media type, but is usuallyeither the compression format or the media type.ReservedSix bytes that must be set to 0.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.100