[MEncoder-users] New quality problem with low contrast images

[Pepe]

Hi.

I'm having again a problem to get a quality image. I recorded a movie with my 
dvd-recorder from a satellite channel. 

Now I'm trying to pass to divx. I'm having problems with some scenes. Scenes 
well illuminated (outside, with sun) look very good. But the movie has a lot 
of scenes with very low light. They are dark but not very dark, maybe they 
have low contrast.

The problem is that those scenes look very bad in my xvid, a lot of blocks, 
very annoying. In the original video, image looks much better. 

This is the command I used:

mencoder -noodml -o temp/video2.avi \
  -oac mp3lame -lameopts vol=0:mode=3:cbr:br=64 \
  -ovc xvid \
  -xvidencopts 
bitrate=1200:nointerlacing:nopacked:pass=2:max_iquant=15:max_pquant=15:max_bquant=15:max_bframes=0 
\
  -vf-add crop=688:560:20:8 \
  -vf-add pp=l5 \
  -vf-add scale=576:432 -zoom \
  -vf-add harddup \
  -force-avi-aspect 4:3 \
  -sws 9   \
  temp/video.avi

I tried everything. I used max_iquant=4:max_pquant=4. I tried different values 
for -sws, also tried yadif instead of l5. I raised the bitrate up to 4000. I 
used b-frames. I used libavcodec instead of xvid. But nothing improved the 
quality, it always remained the same. Removing the filters (crop, 
deinterlace, scale) may improve a little bit, but there's still very visible 
blocks. And anyway I don't want to make a video with such a high resolution 
(720x576) because I would need a bigger bitrate.

I also tried quant_type=mpeg. With that option the image is very different, 
the blocks are smaller but there are even more, all over the whole image 
and are even more annoying.

If I use hqdn3d after the other filters, yes it removes most of the blocks, 
but image loses a lot of details.

Any idea of how to improve the image?

Or maybe is this a limitation of mencoder or the codecs? I got from internet a 
video with an excelent quality, but in one scene there's a moment when the 
contrast goes down for some seconds, and then the image turns very blocky.

-- 
Pepe