Encoded audio is not good - Add better audio?

[NotSoEasy]

Not enough room to really say what I mean.

I encoded a movie to XviD through VDubMOD.Video looks great but audio is not so great.I went with 128 mp3 but it sounds like I used lower bitrate.
What I want to know is how to add my AC3 audio to the video replacing the crummy mp3 and with minimal encoding.Otherwise I would just re-encode whole movie over.....but that takes ages on my PC so trying to avoid long processing.

TIA

[jagabo]

Open your original file with VirtualDubMod. Export the AC3 track by selecting Streams -> Stream List and pressing Demux.

Open the file you've already converted. Go to Streams -> Steam List. Hilite the MP3 track and press Disable. Press Add and select the AC3 track from above. Back at the main window select Video -> Direct Stream Copy. Then File -> Save as... In a minute you'll have a new file with the Xvid video and the original AC3 audio.

[NotSoEasy]

Thank you !
Very painless!