Format Factory Video freeze - Audio fine

Can anyone help please.

I have to convert some DVD (not copyright nor protected) into MPEG files.
I have downloaded Format Factory 2.07 and run a conversion from the VOB files but the image sticks for many seconds while the audio continues, this happens every 15 - 20 seconds.

Also the result the output file is 30% less than if I create an MPEG using serif Movieplus.

I would prefer to use Format Factory because with Movieplus I have to load all the VOB's into a project, index them, before I can export an MPEG (A much longer process than Format Factory)

Any Idea why FF isnt working properly

Thanks