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

Profile Atom GuidelinesProfile Atom SpecificationThe responsibilities placed upon a writer of a movie (such as QuickTime or a consumer electronics (CE) device)are described in the feature’s Writer Responsibilities section. A description of the algorithm to be used tocalculate values is provided.The feature’s Reader Responsibilities section explains how reading software should interpret the value. In somecases, there are warnings to indicate how the reader must not use the value (for example, not interpreting themaximum bit rate value as the current bit rate).Profile Atom SpecificationDefinitionAtom type'prfl'ContainerMovie atom ('moov') or track atom ('trak')MandatoryNoQuantityZero or oneAt the movie level, the profile atom must occur within the movie atom before the movie header atom. A readermay stop the search for the profile atom once the profile atom or the movie header atom is found. Becausenew atoms may be introduced into the movie atom (type 'moov') in the future, a reader must not expect thefirst child atom of the movie atom to be either the profile (type 'prfl') or the movie header ('mvhd') atom.This rule allows for new atoms in the future but still accommodates readers that do not want to perform anexhaustive enumeration of all the child atoms in a movie atom.The profile atom expresses profiles or feature codes for features that occur in the movie. The list is not necessarilyexhaustive, and there may be multiple profile values recorded for the same profile code. For example, if thereare two independent sequences of MPEG-4 video in the movie, using different profile-level IDs, both mightbe recorded here.Each feature is either universal or is documented in a specific specification, identified by a brand as used inthe file type atom. The only brands that should occur in a given profile atom are the universal brand or brandsthat occur in the file type atom in the same file.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.394