Audio conversion (Avi to DVD): separate or together with video?

[kthan]

I am doing a conversion from AVI (xvid) to (VCD) DVD and have some questions about audio conversion. In virtualdubmod (or virtualdub), I convert audio part into wav file. Then, I convert video file to mpeg2 at TMPGEnc plus.

In this process, would it be better to process video and audio separately? I found that it would be better if I am using TMPGEnc (plus) because their audio processing is not always optimal. If so, I don't even have to put my wav file (processed at virtualdub) at the time of video conversion at TMPGEnc? Instead, I can put audio and video file separately into a dvd authoring program (like TMPGEnc or DVD-lab)? (But, i couldn't find a way to add video&audio separately in these programs. Or, I can simply put wav file in the audio section at TMPGEnc and process together with video files. To what extent the difference in the quality of audio I can find between these two options?

Also, what would be the best audio format to make dvd (wav, ac3, mp2)? how to set bit rate (192kbps or 320, or else) for best result?
What would be the best software to process (convert) audio files (Virtualdub, ffmpeggui, else)?

[guns1inger]

When I do this type of conversion, I use virtualdubmod to save the audio as an uncompressed wav, then load it into sound forge and output it as AC3. You can do the same with ffmpeggui. I then encode the video seperately with CCE (whose audio processing is pretty crap as well), usually through an avisynth script to resize and filter the video. I then use DVD Lab Pro to put it all together again at the end.

In DLP, just import the video and audio as seperate assets, then drag them both to the same Movie object.