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

Profile Atom GuidelinesNote Profile atoms are deprecated in the QuickTime file format. The information that follows isintended to document existing content containing profile atoms and should not be used for newdevelopment.This appendix introduces and defines some of the ways that profile information about a QuickTime movie filecan be summarized in a profile atom near the beginning of the file, so that software reading the file can easilydetermine some aspects of its features and complexity.The information in this appendix should not be seen as a replacement for, or even a functional overlap with,the definition of the file-type atom. The file-type atom expresses which specifications a file is compatible with:reading software should not attempt to play files unless they are compatible with one or more specificationsthe reader implements, and should not refuse to play a file if it is marked as so compatible. However, readingsoftware may use profiling information to issue warnings, request user decisions, and so on.Reading software should not present excessive warnings to the user in the absence of summarized features.Additionally, readers are encouraged to try to play content even though crucial profile information is missingor incomplete.Profiles may exist at the movie level or the track level. Track-level profiles summarize features of that trackonly. Movie-level profiles may summarize features across tracks or summarize features that are only relevantat the movie level (for example, the movie’s maximum bit rate).If the movie contains runtime variables that might affect a feature, such as the presence of alternate tracksthat would affect the movie bit-rate, the affected feature should either be absent or report the worst case (forexample, the highest bit-rate).If a feature value cannot be accurately represented (for example, the value is not an integer, but the field isformatted as an integer) then the value should be rounded up to the nearest representable value.About This AppendixThe technical content of this appendix begins with a discussion of the structure of the profile atom, whichholds an array of feature codes and values. Next is an enumeration of the currently included profile features,each described in a feature description section.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.393