---

Modifier Tracks

Track references and modifier tracks create dynamic relationships between tracks in a QuickTime movie. Track references describe the relationship between tracks; for example, one track’s output can be connected to an input of another track, or two tracks may be related as alternate versions, to be used in different languages. Track references are used to create modifier tracks, alternate tracks, and chapter lists, and to relate timecode tracks to segments of other tracks.

A modifier track does not present its data as a video or audio track normally does; instead it uses its data to modify the presentation of other tracks. For example, the output of a video track can used as the source of image data for a sprite track or effect track, or the output of a tween track can be used as the source of the volume setting of an audio track. This chapter discusses several special modifier track types, including:

• Alternate tracks. These are typically different versions of a track to be used in different circumstances, such as multiple text or sound tracks in different languages, or different bit-rate video tracks for optimal display on faster or slower computers.

• Chapter lists, sets of named entry points into a movie that can be jumped to either programmatically or through the user interface.

• Timecode tracks. They contain timecode information, typically gathered from a source external to QuickTime (such as SMPTE timecodes). They relate this timecode data to segments of other QuickTime tracks, such as video, audio, and text tracks.

This chapter assumes that you are familiar with QuickTime tracks in general and the QuickTime functions used to determine and change the display characteristics of movies and tracks.

Contents:

Track References
Creating Modifier Tracks
Creating Movies With Modifier Tracks
Manipulating Media Input Maps
Working With Alternate Tracks

---