average bitrate
mencoder “source.avi” -ovc x264 -x264encopts bitrate=1000:pass=1:threads=3:qp_min=1:qp_max=40:turbo=1 -oac copy -o /dev/null
mencoder “source.avi” -ovc x264 -x264encopts bitrate=1000:pass=2:threads=3:qp_min=1:qp_max=40 -oac copy -o “autput.avi”
ref:
http://web.njit.edu/all_topics/Prog_Lang_Docs/html/mplayer/encoding.html