need program to add additional audio track to .avi file

[pathumx]

I have a .avi file that already has 2 different audio tracks on it and a .ac3 file that i want to add as a 3rd audio track. my googling skills have failed me.

 

[pathumx]

bonus question: is there a way i can take the audio tracks and subtitles from the avi and add them to an mkv file of the same video? i have a .sub file if that helps...

 

[pathumx]

found the answer. used the program here
http://www.bunkus.org/videotools/mkvtoolnix/downloads.html and the only additional thing i had to do was download a srt file for my video.