If you have a video in avi form, and this is supposed to have finished two tracks, while the order of the tracks but must be reversed, ie the sound track that was originally in the video is the result of the second track to be helping the following two commands:

/ / Video + external sound track = new again with a sound track
input.avi mencoder-audiofile externes.mp3-oac copy-ovc copy-o temp.avi

/ / New video + 2 soundtrack = finished video with 2 audio tracks
avimerge getauschte_tonspur.avi-o-i-p temp.avi input.avi

Originally I wanted to mplayer and dumpstream, and then directly by avimerge 2x (once with the first track and once with the second audio track) to make. avimerge but has obvious problems with certain avis, which are then "avilib: not an avi file" auspuckt and cease working.

mencoder spits while the first merge some error (1 duplicate frame (s) and skipping frames - the latter will probably be due to false detection of Framereate) from, but the avi works then either via vlc, as in mplayer via VDR.
If necessary. I look even if I have an avi header fix the NEN find missing index repaired, which can lead to asynchrony in play and possibly also for the error messages from mencoder, and is responsible for the collapse of avimerge.

The two CLI commands I made forum.doom9.org and the study of the respective man pages.