QuickTime 4 Reference

Preloading Tracks

There are occasions when it may be useful to preload some or all of a track's media data into memory. For example, if you are developing an application that plays several movies at once, you may want to load the smaller movies into memory in order to reduce CD-ROM seek activity. Text tracks, which are typically rather small, are good candidates for preloading; in many cases you can load a movie's entire text track into memory. Another good use of preloading is to preload small music tracks that play over scene changes, giving the interactive experience a more continuous feel.

QuickTime 2.0 expanded your options for preloading tracks. In the past, applications could use the Load...IntoRAM functions to preload a movie, track, or media. Now you can establish preloading guidelines as part of a track's definition. The Movie Toolbox then automatically preloads the track, according to those guidelines, every time the movie is played, without any special effort by applications. You establish these preloading guidelines by calling the new SetTrackLoadSettings function. (See "Enhancing Movie Playback Performance" for more information about this function). Note that the preloading information is preserved in flattened movies.