FFmpeg is a command-line video converter. It can convert among a variety of formats, including the iPod-compatible MP4 format. If you have a VOB file in a Video_TS folder (a standard format for DVD rips), you can convert it to an MP4 with a single command. This will not only change the file format, but update all the video codecs to ensure full MP4 compatibility.
Copy and paste the following into the command line:
ffmpeg -i input -acodec libfaac -vcodec mpeg4 -b 1200k -mbd 2 -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -metadata title=X output.mp4
Change "X" to the desired title of your output video and hit Enter.
Type in the location of the VOB file when prompted, then hit Enter again.
Wait for the conversion to complete. FFmpeg will display "OK" when it is done. Depending on the size of your VOB, it could take up to ten minutes.