mixing mp3 and ac3

[ivan_alias]

Do people do this?

I see the option in GKnot but I'm not sure of the benefits?

Is there any point?

Surely you want either the ful ac3 or a goodquality compressed mp3?

What have I missed here?

[elgan123]

There are many situations where you might want 2 (or more) audio tracks. Example: Original mandarin AC3 and english mp3 for CTHD. Or maybe you want the director's commentary and the original soundtrack.