Preload duration
A 32-bit integer specifying the duration, in the movie’s time coordinate system, of a segment of the track that is to be preloaded.
Overview
If the duration is set to –1, it means that the preload segment extends from the preload start time to the end of the track. All media data in the segment of the track defined by the preload start time and preload duration values should be loaded into memory when the movie is to be played.