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

Movie AtomsReference MoviesApplications should play the highest-quality movie whose requirements are met by the user’s system. If thedata reference to the selected movie cannot be resolved—because the file cannot be found, for example—theapplication should recursively attempt to play the next-highest-quality movie until it succeeds or has exhaustedthe list of movies whose requirements are met.If a movie contains both a reference movie atom and a movie header atom, applications should play theappropriate movie indicated by the reference movie atom.If the user’s system does not meet any of the alternate movies’ criteria, or none of the qualifying data referencescan be resolved, applications should play the movie defined in the movie header atom. (The movie defined inthe movie header atom can also be indicated by one of the alternate movie references.)The movie header atom is sometimes used to provide a fallback movie for applications that can play olderQuickTime movies but do not understand reference movies.When parsing a reference movie, the reader should treat the URL or file reference in the reference movie atomas a new starting point, making no assumptions that the reference is a valid URL, or an existing file, or awell-formed and playable QuickTime movie.Reference Movie AtomA reference movie atom contains references to one or more movies as shown in Figure 2-55 (page 120). It canoptionally contain a list of system requirements in order for each movie to play, and a quality rating for eachmovie. It is typically used to specify a list of alternate movies to be played under different conditions.A reference movie atom’s parent is always a movie atom ('moov'). Only one reference movie atom is allowedin a given movie atom.Figure 2-55A 'rmra' atom with multiple 'rmda' atomsReference Movie atomAtom sizeType = 'rmra'Reference movie descriptor atomReference movie descriptor atomReference movie descriptor atom'rmda''rmda''rmda'A reference movie atom may contain the following fields:2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.120