well typically speaking… if your converting a .VOB file to a .AVI (XviD) … in general it’s going to take some loss in quality but considering ‘file size vs quality’ ratio a .avi (XviD) is a pretty good tradeoff as if you select the proper output size (which to keep quality high say 700MB per hour of video (give or take a little)) the final video will be pretty close to the original source but at a much smaller file size.
but a general figure for XviD is… 700MB per hour of video (this is about as close to original source as you can get for the most part) and depending how picky your are you could even get up to around 1 hour and 30minutes per 700MB (just use 128kbps MP3 for the audio instead of the .AC3 track on the DVD)
so if your .VOB file is only 30minutes long you could make a 350MB .avi file and it would be the same as if you did 1 hour @ 700MB… you basically just do the math when it comes to the length of the original .VOB file and you can scale it down if you need to
but in general when i convert my DVD movies to XviD… i usually do this…
-Movies around 1hour and 30minutes = 700MB (and you convert the .ac3 audio track to 128kbps MP3)
-Movies around 2hours+ = 1400MB (and i use the .AC3 audio track from the DVD)
the program i use is ‘Gordian Knot’ (which is basically the manual version (more control over the conversion process) of AutoGK (easier to use for the beginner) which is listed above by Kerry56)
here is ‘newest’ XviD codec which you will need to make .avi (XviD) files with Gordian Knot… http://www.koepi.info/Xvid-1.2.1-04122008.exe