Hi,
Unless you can find a package that'll do this for you, you'll need to:
1. Demultiplex the audio and video
2. Load the audio into something like Audacity
3. Bleep out the bits required
4. Encode the audio back into MPEG format
5. Remultiplex the audio and video again
You could try
mpgtx, though that doesn't appear to have been updated for a while.
For all-in-one solutions that
may work, have a look at
Kdenlive,
Kino,
LiVES and
Cinelerra.
I must admit I usually "cheat" and drop back to Windoze for video-related work (mainly because I've paid for the editing software!), rather than doing it in Linux, but hopefully one of the above will be of use.
If I was in Windows doing this, I'd use TMPGEnc to demultiplex, then Audacity to bleep out, then TMPEGEnc to re-encode the audio, then TMPGEnc again to remultiplex.
Good luck!
- Ali