QuickTime 4 Reference

Track References

Although QuickTime has always allowed the creation of movies that contain more than one track, it has not been able to specify relationships between those tracks. Track references are a new feature of QuickTime that allow you to relate a movie's tracks to one another. The QuickTime track-reference mechanism supports many-to-many relationships. That is, any movie track may contain one or more track references, and any track may be related to one or more other tracks in the movie.

Track references can be useful in a variety of ways. For example, track references can be used to relate timecode tracks to other movie tracks. (See "Timecode Media Handler" for more information about timecode tracks.) You might consider using track references to identify relationships between video and sound tracks--identifying the track that contains dialog and the track that contains background sounds, for example. Another use of track references is to associate one or more text tracks that contain subtitles with the appropriate audio track or tracks.

Track references are also used to create chapter lists , as described below.

Every movie track contains a list of its track references. Each track reference identifies another, related track. That related track is identified by its track identifier. The track reference itself contains information that allows you to classify the references by type. This type information is stored in an OSType data type. You are free to specify any type value you want. Note, however, that Apple has reserved all lowercase type values.

You may create as many track references as you want, and you may create more than one reference of a given type. Each track reference of a given type is assigned an index value. The index values start at 1 for each different reference type. The toolbox maintains these index values so that they always start at 1 and count by 1.

See "Working With Track References" for detailed descriptions of the Movie Toolbox functions that allow you to work with track references.

Chapter Lists