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

Movie AtomsReference Movies'moov' atom must contain both a 'rmra' atom and a 'mvhd' atom. To resolve this datareference, an application uses the movie defined in the movie header atom, ignoring the remainderof the fields in this data reference atom, which are used only to specify external movies.Data reference typeThe data reference type. A value of 'alis' indicates a file system alias record. A value of 'url ' indicatesa string containing a uniform resource locator. Note that the fourth character in 'url ' is an ASCII blank(0x20).Data reference sizeThe size of the data reference in bytes, expressed as a 32-bit integer.Data referenceA data reference to a QuickTime movie, or to a stream or file that QuickTime can play. If the referencetype is 'alis' this field contains the contents of an AliasHandle. If the reference type is 'url ' thisfield contains a NULL-terminated string that can be interpreted as a URL. The URL can be absolute orrelative, and can specify any protocol that QuickTime supports, including http://, ftp://, rtsp://,file:///, and data:.Data Rate AtomA data rate atom specifies the minimum data rate required to play a movie. This is normally compared to theconnection speed setting in the user’s QuickTime Settings control panel. Applications should play the moviewith the highest data rate less than or equal to the user’s connection speed. If the connection speed is slowerthan any movie’s data rate, applications should play the movie with the lowest data rate. The movie with thehighest data rate is assumed to have the highest quality.Only one data rate atom is allowed in a given reference movie descriptor atom.A data rate atom may contain the following fields:SizeThe number of bytes in this data rate atom.TypeThe type of this atom; this field must be set to 'rmdr'.FlagsA 32-bit integer that is currently always 0.Data rateThe required data rate in bits per second, expressed as a 32-bit integer.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.123