Dual audio track

1.Warning

Avidemux can only handle one audio track internally.

Nonetheless, there is a way to add a second audio track, with limited support and no processing at all on that second audio track.

2.Adding a second audio track

Restrictions 

The second audio track must be CBR, that is MP3 CBR or AC3. Period.

Menu 

To add a second audio track, use the Audio->Second Track->xxxx menu. After selecting it, set the output format to avi (dual audio).