[MPlayer-users] Re: Constant Visual Quality

[Rémi Guyomarch]

On Wed, Dec 11, 2002 at 02:23:49AM -0600, Angel wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hi All,
> 	I have a question regarding encoding movies with the lavc
> mpeg4 codec. I know you can specify a constant quantizer when
> encoding a movie... but that does not necessarily result in a
> constant visual quality in the encoded movie.  Basically what I want
> to be able to do is specify a given visual level of quality and have
> the encoder maintain that quality level using a variable bit rate /
> variable quantizer. I could just specify a quantizer level of 2 (or
> 1 even) and get the best possible quality encoding but I don't want
> to waste space encoding scenes with more bits then are necessary to
> achieve the quality level I want.

The problem is how to define "visual quality". There isn't any magic
formula which tell you "this part has a visual quality of 37.12 and
this one has a VQ of 29.10". The best approximation we have right now
is the value "quantizer" and the associated algorithm.

No one yet has modelized (sp?) the humain eyes and brain.

If you want a non-integer average quantizer (eg 2.27), you can play
with B frames and options vmax_b_frames, vb_qfactor, vb_qoffset,
vi_qfactor and vi_qoffset (and read DOCS/tech/libavc-options.txt). You
can try tcplx_mask and naq too.

-- 
Rémi