strange bitrate problem

[sakuya_su]

I have this strange problem with some videos encoded using MEncoder:

I set the bitrate to 710 and screensize of 320x240, so the comandline looks like this:
-ovc lavc -lavcopts vpass=1:vbitrate=710:vcodec=mpeg4 -ffourcc DIVX50 -vf scale=320:240

now, after the video is converted, both Mencoder and GSpot says the encoded AVI file have a bitrate of 260kbps??

does nayone know what is happening?

thanks

[sakuya_su]

also, the file size reflects this reduction in bitrate, like the original was a 240mb mkv, now the converted file is only 68mb

however when I watch it, during fast scenes and scenes with pretty colours (XD), i do not see the blockyness that come with such a low bitrate(280)