Playing DVD

Hello,
Recently downloaded a whole movie, it is MP4 format. Since this cannot be played on home dvd player, had to convert it into AVI , in user manual it says AVI can be played - but it did not. So then I converted it into VOB format, but again dvd refused to play it. Finaly had to use a dvd authoring program, wasted some hours to work on it and finally got my dvd with menus playing.
My question: Since all files in the dvd folder are vob, why the one vob I made on the first time did no play.
The converstion done with "format factory".
Some answers will be appreciated
Thanks
Motim

Just one .vob file is not up to DVD play back specs. That's why you had to use a authoring program.