The way you're doing it now would result in two lots of quality loss - the downconversion from tape to DVD in the first place and then, if you change the aspect ratio in Vegas, you're going to have to then re-encode the output back to DVD again. Taking an already highly compressed file and compressing it again, even to the same size, always results in loss because you have to recompress the blocking and encoding artifacts from the previous encode. So what you're doing - the Mini-DV encoding results in some encoding artifacts in the image, when the tape is passed to the standalone DVD recorder it sees these artifacts as though it was detail in the frame, and so it needs to compress these too, not just the actual picture content. This compression results in even more encoding artifacts, especially because the DVD bitrate will be so much less than the mini-DV. When you stretch it and encode it out again from Vegas, Vegas will see the original Mini-DV artifacts, the standalone DVD recorder artifacts, and have to compress all of this in addition to the actual content. This results in even more artifacts and blocking, which you then see. Even if you don't think you can see any artifacts at the mini-DV or standalone DVD level, they are certainly there, and the computer can see them (as added 1s and 0s). I hope you get what I'm saying, it's a little hard to explain.
That said, if all you want to do is fix the aspect ratio you don't need to re-encode the DVD at all (or use Vegas). Aspect Ratios on all DVDs are all handled by putting commands in the header of the MPEG-2 file on the DVD that tells the player to stretch the footage to either 4:3 or 16:9 on playback. The standalone has set this header to play back at 4:3, but there are simple programs that will take the DVD, just change the little bit of info in the header, then when you burn it it will play back correctly.
thanks, that second option you described sounds like something i want to try if it would eliminate a second layer of quality loss. what is one of those simple programs you refer to? could i render the project i've created in vegas as MPEG-2, in 4:3 without reencoding, and then just change the header directly on this MPEG file?
also...maybe someone can help me with one more thing. sorry, i can hold my own with audio but i'm a bit of a noob with video. in vegas, how do you fill gaps of missing video, with a picture, for instance, so you don't have to just look at a black screen. like, when you change minidv tapes but you're recording an external audio source, when you mix the 2 you'll have a small section there with audio but no video. i don't even have to do anything fancy like looping video clips in that gap or anything, just a still picture would suffice.
EDIT: to answer my own question (1st paragraph), it looks like DVDPatcher would do the trick? does anyone else use this?
still can't figure out how to do what i want in vegas though, if anyone can help.