[MPlayer-users] Re: Constant Visual Quality

[D Richard Felker III]

On Fri, Dec 13, 2002 at 04:44:22AM -0600, Angel wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> > So, if I used vqscale=4 with naq and fairly large values for the
> > masking parameters, I might be likely to see lots of frames using
> > qscale 2,3,4,5,6,7 across different macroblocks as needed, but with
> > the average sticking around 4. However, I haven't actually tested such
> > a setup yet, so it's just speculation right now.
> 
> > Have fun playing around with it.
> 
> 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