Firstly i would use mplayer to get a info on the file : mplayer file.vob
So i can see wich audio tracks are there, how long etc.
Let's say we have only one audio track in AC3.
mencoder input.vob -ovc x264 -oac copy -of avi -o output.avi That would be the setting for mencoder to convert the vob to a simple avi file in h264 ( h264 is in my opinion the best codec to convert a vob or a DVD to before you start to encode the final file )
I think you do get what the commands are, but for those who read here who do not know : -ovc = output video codec ; -oac = output audio codec ; -of output format -o output ( ;)
So, after this i let ffmpeg handle the rest :
ffmpeg -i output.avi -vcodec xvid -s 640x480 -b ( what ever you want )1500 -acodec aac -ar 48000 -ab 128 -r 29 final.avi
Commands : -vcodec = video codec; -s = Size; -b = video bitrate; -acodec = audio codec; -ar = audio rate; -ab = audio bitrate; -r = framerate
That would for example how i would encode that file. In case of mplayer i recommend to read the online documentation since they have already some exaples for encoding in it for anything you could encode a file to.
In case of ffmpeg, you dont realy need a documentation. It's plenty to just type ffmpeg in the console and look up the commands you need.
Edit : As you can see, i dont encode the stuff directly to the final file wich i want to play. I use mencoder to convert it to something i can more easy reencode with ffmpeg. You could encode the whole thing with mencoder to the final xvid. But the commands for that are long and confusing ( well, for me at least )
You would have to go live -lavc lavcopts xvidblablubb with many : and other stuff wich only confuse you when you look for a wrong option wich causes an abort or mencoder to not even start. Therefore i encode to h264, copy the audio track and then do the rest with ffmpeg since i have a seperated command for almost any option i wnat to set.