Ac3 and m2v merged

[robertrej]

I have been trying to combine an ac3 audio file with a m2v file
but each time the various software programs seem to encode
the ac3 to mp2.A very big difference in quality of course so
can I combine the two or is it simply not possible.
I have been using free software and would like to continue
down that path.

Both files are equal length and play ok but the audio output
is not ac3 just pcm.

Please help
Thanks
Bob