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

Profile Atom GuidelinesUniversal FeaturesFeature Value AlgorithmThis value is calculated by examining the dimensions of all visual tracks and computing the maximum combineddimensions, including the effect of track matrices and the movie matrix. For example, if two video tracks playside-by-side in the movie, and the tracks and movie all use the identity matrix, this value will be the largest ofthe two tracks’ heights and their combined width.Reader ResponsibilitiesA reader of this feature code should compare the recorded value with its own video size limits.The reader should not interpret the value of this feature as the current video size. To determine the currentvideo size, the reader should use the dimensions of all currently displaying video tracks, their matrices, andthe movie matrix.CommentsThe width and height correspond to the maximum visual area needed to display the movie.The summarized width and height should take into account all components of all track matrices and the moviematrix. The goal is to understand the maximum contribution of all tracks to the movie’s bounds.For the case where there is a single video track with an identity track matrix, the movie’s maximum video sizefeature would typically have the same value as the track’s maximum video size feature.Maximum Video Size in a TrackContaining profile atomTrack (video), moviepart-ID0x20202020 (universal feature)feature-code'tvsz'feature-valueA 32-bit packed structure holding width and height of the largest picture buffer needed for a video track.Feature ValuesA packed structure in a 32-bit value:struct {2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.412