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

Profile Atom GuidelinesUniversal FeaturesWarning Use of the "clean aperture" sample description extension does not affect the value of thetrack visual size, as the picture buffer is needed immediately after decoding, prior to any clean apertureclipping.Maximum Video Frame Rate in a Single TrackContaining profile atomTrack (video), moviepart-ID0x20202020 (universal feature)feature-code'vfps'feature-valueAn unsigned fixed-point (16.16) number holding the maximum video frame rateFeature ValuesThis is an unsigned fixed-point (16.16) number holding the maximum 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.Writer ResponsibilitiesA writer of the Maximum Video Frame Rate feature should record a 16.16 fixed-point value that is equal to orgreater than the current video frame rate. A writer (such as a CE device) may choose to record a constant forthe feature based on its current recording mode, even if the actual frame rate is less.A writer of a new video track (such as a CE device recorder) may set the maximum frame rate feature value toa value set during video encoder initialization, so long as this frame rate is never exceeded.If the current calculated frame rate is fractional (such as 22.3 fps), a writer may choose to round the value upto the nearest integer value (such as 23.0 fps for 22.3 fps).A writer calculating the video frame rate using the video track’s sample table should not consider the first orthe last sample duration if they differ from the other sample durations. The reason for this is that capturedmovie files often have longer or shorter first and last sample durations. By not considering them in thecalculation, a more accurate calculation is achieved.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.414