[MPlayer-users] mencoder, getting much lower vbitrate than I requested

[Andreas]

I routinely use the following to convert 440Mb mpeg-1 files to
"mpeg4" (currently with mplayer-0.90rc4):

BR=960
mencoder "$infile" -o frameno.avi -ovc frameno -oac mp3lame -lameopts abr:br=128 -srate 44100
mencoder "$infile" -o "$outfile" -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vhq:vbitrate=$BR:vpass=1:aspect=4/3
mencoder "$infile" -o "$outfile" -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vhq:vbitrate=$BR:vpass=2:aspect=4/3

However, for *some* mpeg input files, the resulting avi file has a video bitrate way below 960, sometimes
around 300 or 400.

Does this mean that the quality of the resulting avi file can't get any better? is this a problem with
the original mpeg? I even tried some absurd values such as 4096 for vbitrate, but it "saturates" at
some top (and low) value.