Alternate group
A 16-bit integer that identifies a collection of movie tracks that contain alternate data for one another.
Mentioned in
Overview
This same identifier appears in each 'tkhd' atom of the other tracks in the group. QuickTime chooses one track from the group to be used when the movie is played. The choice may be based on such considerations as playback quality, language, or the capabilities of the computer.
A value of zero indicates that the track is not in an alternate track group.
The most common reason for having alternate tracks is to provide versions of the same track in different languages. The following table shows an example of several tracks. The video track’s Alternate Group ID is 0, which means that it is not in an alternate group (and its language codes are empty; normally, video tracks have the appropriate language tags). The three sound tracks have the same Group ID, so they form one alternate group, and the subtitle tracks have a different Group ID, so they form another alternate group. The tracks would not be adjacent in an actual QuickTime file; this is just a list of example track field values.
Track type | Alternate group ID | Extended language tag | Language code |
|---|---|---|---|
video ( |
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sound ( |
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sound |
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sound |
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subtitle ( |
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subtitle |
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