ogg quality problem with ffmpeg

[asm4 <asm4@lehigh.edu>]

i upgraded my unstable-debian last week and i am seeing quality issues 
with ripping sound from a .vob file. when i do:
ffmpeg -i MTK_RECORD_VOLUME1-1.vob -f ogg -vn out.ogg
the nominal bit rate shown by xmms or mplayer on out.ogg is 0k and 
average bit rate is 41.7kbps

if i dump out a .wav from the same vob file using mplayer and then 
convert to ogg using audacity, the quality is much better and xmms shows 
(in file info) a nominal bit rate of 160kbps and average of 113.4kbps.

i have 0.cvs20070307-6 of ffmpeg and this seems to be the latest 
version. am i doing something wrong? or is there a better way of getting 
an ogg file from vob. i tried different -ab options with ffmpeg but did 
not seem to help.

thanks
ashutosh