mix audio

hello everyone...

I am trying to put few audio files on a video file....

for instance ...

second 0 one audio
second 12 one audio
second 45 one audio

where the audio files overlap each other

I couldn't find any command line tool which dose this... so what i did is to join the mp3 files by mp3wrap.exe and then mux it with video file by mencoder.exe... but thats not exactly what i need... caz mp3wrap doesn't mix the mp3 files...it just joins them by order!

and by the way what do u call doing this?? is it mixing or muxing or what??

Thanks
Zoha