Hello rds_correia:
I just started playing w/ ffmpeg, and thanks to kwag, as well as posts regarding ffmpeg, I was able to work with .VOB files as well.
I am following the script tha kwag posted a couple of days ago. Just in case, you can find it here:
http://www.kvcd.net/forum/viewtopic.php?t=6153
On my first tries, VOBs were not working for me, only because I forgot to enter the ,VOB extention. Something else you may try, just for kicks, change the fps to 29.76 and see what happens, after all, we are just playing around
Regards
Totonho03