One thing to keep in mind is that many codecs have width/height/colour-depth limitations. Having everything evenly divisible by two or four is a good rule-of-thumb. In the case of DivX, at least, width must be a multiple of four, and height must be a multiple of two. And I don't think it supports 16-bit colour. I just gave DivX 5.1.1 (non-pro) a try with my installation of Pro Pack and it appears to work fine.