The problem is that lavc mpeg-4 uses quantization level 31 for more than 10% of the video. I'm not sure if it has anything to do with it, but the source mpeg has some very dark portions (it's the 16th episode of the ABC show Lost). I was also using dd to cut the commercials before encoding, so there are some damaged mpeg2 frames near the cutpoints. Here are the commands I've used for encoding: First pass: mencoder -vfm ffmpeg <hdtv-1080i-mpeg-ts-file> -tsprog 1 -vop hqdn3d=4:3:3,scale=1024:576,harddup,softskip,filmdint=crop=1908:1078:4:0 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:psnr:mbd=2:v4mv:aspect=16/9:vmax_b_frames=1:trell:cbp:cmp=2:precmp=2:subcmp=2:vb_qoffset=0.5:vpass=1:vdpart:vpsize=1000:vqcomp=0.75:lmin=4:lmax=4 -force-avi-aspect 16/9 -sws 1 -fps 29.97 -ofps 23.976 Second pass: mencoder -vfm ffmpeg <hdtv-1080i-mpeg-ts-file> -tsprog 1 -vop hqdn3d=4:3:3,scale=1024:576,harddup,softskip,filmdint=crop=1908:1078:4:0 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:psnr:mbd=2:v4mv:aspect=16/9:vmax_b_frames=1:trell:cbp:cmp=2:precmp=2:subcmp=2:vb_qoffset=0.5:vpass=3:vqcomp=0.75:vbitrate=1000:vdpart:vpsize=1000 -force-avi-aspect 16/9 -sws 1 -fps 29.97 -ofps 23.976 The 2 passes take more than 4.5 hours, so it's not easy to experiment with changes. I've posted about a similar bug before, see http://mplayerhq.hu/pipermail/mplayer-advusers/2005-February/001093.html but I got no reply. This problem happens very often in 3-pass mode, but this is the first time I see this in 2-pass mode. I've uploaded badquant.tar.bz2 to mplayerhq incoming which contains the passlog files from both passes (pass1.log, pass2.log), the psnr file (pass2.psnr) and the output of mencoder in the second pass (pass2.out). All this was done with the Feb 28 CVS of mplayer and libavcodec. Thanks, Zoli