Thank you the DJ four your answer.
I can´t find the options 'abit' and 'vbit' in the documentation. Can u say me in which document I can find them (Videolan howto, or vlc userguide). To which module do they belong?
P.S: I´m using VLC 0.7.2. Pehaps you mean the options 'ab' and 'vb' of the "transcode" module!