I am trying to put few audio files on a video file by command line tools....

for instance ...

second 0 audio1.mp3
second 12 audio2.mp3
second 45 audio3.mp3

and the audio files overlap each other....

the only thing i got was using mencoder which joins the audio files by order ...but that's not what i need...
first, i want the audios to overlap each other and second the software ask for specific second to insert audio...

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

(excuse my poor English! )
Thanks
Zoha