Interleaving Movie Data

QuickTime Movie File Format Specification, May 1996

Interleaving Movie Data

In order to get optimal movie playback, you must create the movie with interleaved data. The data for the movie is placed on disk in time order so the video, sound, and other data for a particular time in the movie are close together in the file. This means that you will have to intersperse the data from different tracks. To illustrate this, consider a movie with a single video and a single audio track.

Figure 0-45 shows how the movie data was collected, and how the data would need to be played back for proper synchronization. In this example, the video data is recorded at 10 frames per second and the audio data is grouped into 1/2-second chunks.

Figure 45 Noninterleaved movie data

After the data has been interleaved on the disk, the movie data atom contains movie data in the order shown in Figure 0-46 .

Figure 46 Interleaved movie data

In this example, the file begins with the movie atom ('moov' ), followed by the movie data atom ('mdat' ). In order to overcome any latencies in sound playback, at least one second of sound data is placed at the beginning of the interleaved data. This means that the sound and video data are offset from each other in the file by one second.