[MPlayer-users] Mixing two or more audio streams in one

[yurysub at gmail.com]

I have a movie (AVI) with two audio tracks: the first is original
language track with all sounds of the movie, the second is translation
track without any sounds of the movie.
Applying 'mplayer -aid 1 -aid 2 movie.avi' plays only one audio track as
expected.
How can I mix these tracks while playing movie by mplayer?
Are there some tools for Linux to do mixing two or more audio streams in
one?

Thank you in advance.

-- 
Best regards,
Y.