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

Profile Atom GuidelinesUniversal FeaturesFeature Value AlgorithmThis feature value may be calculated as the inverse of the smallest sample duration in the video track or tracks.If the value is written for a newly recorded video track it may be a value established during initialization of thevideo encoder, so long as the frame rate is not exceeded.Reader ResponsibilitiesA reader of this feature code should compare the recorded value with its own video frame rate limits. It shouldnot expect exact values.The reader should not interpret the value of this feature as the current frame rate. To determine the currentframe rate, the reader should use the video track’s sample table.CommentsA writer may choose to round up any fractional value of the fixed-point number to the nearest 16-bit integerleaving the lower 16 bits of the Fixed value set to 0. So, in the case of the 29.97 approximation of 0x001DF853,the writer could round this up to 0x001E0000 (which equals 30).Average Video Frame Rate in a Single TrackContaining profile atomTrack (video), moviepart-ID0x20202020 (universal feature)feature-code'tafr'feature-valueAn unsigned fixed-point (16.16) number holding the average video frame rateFeature ValuesThis is an unsigned fixed-point (16.16) number holding the average video frame rate. The integer portion ofthe number can range from 0 to 65535.Examples: 25 fps = 0x00190000; 24 fps = 0x00180000; 29.97 = 0x001DF853 (close approximation of a 30000/1001ratio). The value may be rounded up to the nearest integer.When present in a movie-level profile, these atoms document the average video frame rate of each track inthe movie.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.415