I am converting from MPEG2 to Divx using virtual dub. In the DIVX codec VBR, there is the options 1-pass, 1-pass quality based, 2 pass first pass and 2-pass second pass. Also in general parameters there is keyframe. I have seen both of these mentioned in these forums in regards to video quality. I tried encoding with 2-pass second pass, but virtual dub wouldn't let me do that, it produces some error message. I've also tried with 2 pass first pass but after encoding, it produces nothing but a black screen. Can somebody explain to me what these options do?