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

Movie AtomsMedia AtomsComponent typeA four-character code that identifies the type of the handler. Only two values are valid for this field:'mhlr' for media handlers and 'dhlr' for data handlers.Component subtypeA four-character code that identifies the type of the media handler or data handler. For media handlers,this field defines the type of data—for example, 'vide' for video data, 'soun' for sound data or ‘subt’for subtitles. See “Media Data Atom Types” (page 154) for information about defined media data types.For data handlers, this field defines the data reference type; for example, a component subtype value of'alis' identifies a file alias.Component manufacturerReserved. Set to 0.Component flagsReserved. Set to 0.Component flags maskReserved. Set to 0.Component nameA (counted) string that specifies the name of the component—that is, the media handler used when thismedia was created. This field may contain a zero-length (empty) string.Media Information AtomsMedia information atoms (defined by the 'minf' atom type) store handler-specific information for a track’smedia data. The media handler uses this information to map from media time to media data and to processthe media data.These atoms contain information that is specific to the type of data defined by the media. Further, the formatand content of media information atoms are dictated by the media handler that is responsible for interpretingthe media data stream. Another media handler would not know how to interpret this information.This section describes the atoms that store media information for the video ('vmhd'), sound ('smhd'), andbase ('gmhd') portions of QuickTime movies.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.85