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

Movie AtomsReference MoviesReference MoviesA QuickTime movie can act as a container for a set of alternate movies that should be displayed under specifiedconditions. One of these movies may be contained within the same file; any others are included by reference.For example, a QuickTime movie can contain a list of references to movies having different data rates, allowingan application to choose the best-looking movie that can play smoothly as it downloads over the Internet,based on the user’s connection speed.A movie that contains references to alternate movies is called a reference movie.A reference movie contains a reference movie atom ('rmra') at the top level of the movie atom as shown inFigure 2-54 (page 119). The movie atom may also contain a movie header atom, or it may contain the referencemovie atom alone.Figure 2-54A movie atom containing a 'rmra' atom instead of a 'mvhd' atomMovie atomAtom sizeType = 'moov'Reference movie atom'rmra'The reference movie atom contains one or more reference movie descriptor atoms, each of which describesan alternate movie.Each reference movie descriptor atom contains a data reference atom, which specifies the location of a movie.Note Movie locations are specified using QuickTime data references. QuickTime supports multipletypes of data reference, but alternate movies are generally specified using data reference types ofeither url ('url ') or file alias ('alis').A reference movie descriptor atom may contain other atoms that specify the movie’s system requirementsand the movie quality. If so, there will be an atom of an appropriate type for each requirement that must bemet for the movie to play, and there may be a quality atom as well.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.119