I have a DivX movie which has aspect ratio of 4:3 (640:480) but that is wrong. I can change the ratio in players but I would like to convert a movie so that it opens in correct ratio every time. I think I can add resize filter in Virtual Dub. Does that mean I have to recode the movie again. Do I lose any quality doing that and are there any options I should be careful about. Also if original movie uses codec DIV3 and I recode it now, can I use DIV5. Thanks.
You answered all your questions. Yes you will have to re-encode, yes it will lose quality and yes you can use DIVX 5.xx. Note, if the clip is heavily compressed, than resize down, but you'll have to resize down a lot or it will look pretty bad. Better of using DIV3 low in full quality and bitrate.