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

Movie AtomsOverview of Movie AtomsNote Additional atoms may be present in a one-track QuickTime movie file that do not appear inFigure 2-1 (page 39).The Movie AtomYou use movie atoms to specify the information that defines a movie—that is, the information that allowsyour application to interpret the sample data that is stored elsewhere. The movie atom usually contains amovie header atom, which defines the time scale and duration information for the entire movie, as well as itsdisplay characteristics. Existing movies may contain a movie profile atom, which summarizes the main featuresof the movie, such as the necessary codecs and maximum bit rate. In addition, the movie atom contains a trackatom for each track in the movie.The movie atom has an atom type of 'moov'. It contains other types of atoms, including at least one of threepossible atoms—the movie header atom ('mvhd'), the compressed movie atom ('cmov'), or a referencemovie atom ('rmra'). An uncompressed movie atom can contain both a movie header atom and a referencemovie atom, but it must contain at least one of the two. It can also contain several other atoms, such as aclipping atom ('clip'), one or more track atoms ('trak'), a color table atom ('ctab'), and a user data atom('udta').Compressed movie atoms and reference movie atoms are discussed separately. This section describes normaluncompressed movie atoms.Figure 2-2 (page 41) shows the layout of a typical movie atom.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.40