Re: [MPlayer-users] Re: Constant Visual Quality

[Martin Pavon <martin_199ar@xxxxxxxxxxxx>]

On Fri, Dec 13, 2002 at 10:48:13AM -0500, D Richard Felker III wrote:
> > Thank you very much for your thorough and well written explanation. I just 
> > have one last question. In my experience, the lavc mpeg4 codec seems to 
> > have 
> > the most problems (visual quality wise) encoding scenes that 1) contain 
> > smoke 
> > or clouds (this is doubly true for dark scenes) 2) scenes containing large 
> > solid color areas. In both cases, the encoded video looks blocky even when 
> > a 
> > high bitrate or a qscale of 2 is used. Since I watch most of my videos on 
> > T.V., this is the type of visual artifact that I most want to avoid because 
> > its very apparent. Do you have any specific recommendations to improve the 
> > visual quality of these types of scenes.
> 
> I've seen reports of this before, but it's never happened to me. My
> best guess is that you're trying to encode with too low a bitrate, and
> scenes before the smoke/clouds/fog are very complex and cause the rate
> control code to consume more bits than the average bitrate you
> requested, then it has to compensate later by encoding the scenes
> you're talking about with way too few bits. Could you perhaps provide
> some more examples (uploading them to mphq would be fine) or try
> encoding the relevant scenes with vqscale=2 or 3 and see if that looks
> good?
> 
> BTW, one way to improve quality of specific scenes is to use the
> vrc_override lavcopt to specify your own qscale for particular ranges
> of frames. But if there really is a general problem, it should be
> fixed in lavc so that this isn't necessary in the future.
> 
> Rich
> 

Hi Rich!!!

I think I sent the two samples that Rémi talk about in this thread. I can't
fix  an embarrassing  500 error  at my  site,  so if  you want  to see  the
samples, I can  try to upload them to mplayerhq.hu/incoming  this week end;
one sizes 26mb and the other 42mb.

Besides, I have ... Well, I believe I  have a sample from "the city of lost
children" which I  guess it show the  rate control you say.  When I encoded
the movie I found a very ugly blocking problem in one scene, when I cut off
a sample  to upload it  and encoded this piece,  I found that  the blocking
problem almost vanish... Actually, I've just  tried to encode the sample to
see if  the problem is fixing  or not, I've  found that I can't  encode the
whole sample,  may be  this is due that I splited &  join the  file several
times until I got  the sample (with split and cat) , but  I can see it with
mplayer so ... If you want it, I  can upload it too (57mb). 

Finally, if you are  intersting in all of this artifacts,  I can upload the
infamous sample of the 500 error (I  believe you are one of the people that
tell me about this).

Regards,

Martín

-- 
Martín Pavón
martin_199ar@xxxxxxxxxxxx
http://mate.dm.uba.ar/~mpavon/