I need a way to batch convert 720p video files from avc1 to xvid in Ubuntu 10.04. I'm not terribly concerned about file size, but I do wish to retain the picture quality as much as possible. I believe the audio is encoded as aac, which is fine for my purposes.

What would be the best and easiest way to do this? I've tried using Handbrake. During my first attempt, I had it using ffmpeg to convert to MPEG-4, but that just gave me a super-low quality video at twice the file size. Trying h.264 now, so we'll see how that works out. But just in case it doesn't pan out so well, what other ways do you recommend?

I was thinking I'd write a bash script to reencode the files one by one, but the problem is that I have very little knowledge about codecs and containers and whatnot - so I wouldn't know what parameters I would pass ffmpeg/mencoder.