[MEncoder-users] x264 [error]: no ratecontrol method specified

[Nicolas George]

Le quintidi 15 germinal, an CCXVI, Corey Hickey a écrit :
> Roughly, 'qp' sets a constant quality per frame,

To be perfectly, qp sets a constant quantizer, which is roughly related to
quality, but not directly. There is another mode, crf, which is supposed to
be more akin to constant quality.

>						   making multipass
> encoding useless--if the quality is constant, each pass is identical,
> since there's no way to control how many bits each frame uses.

That, now, is quite wrong on the theoretical point of view: even with
constant quantizer, there is a choice to be made between I- and P-frames
(and B-frames if they are enabled). This choice can benefit from knowledge
of the global structure of the movie, especially the position of scene
change.

The way I see it, the choice between I- and P-frames is very akin to the
line-breaking problem in text formating tools (without justification, and
with no space elasticity). The naive, glutton algorithm will cram as much
words as possible on each line before breaking. But there are algorithm that
can use the whole paragraph to find the best breaks; see the TeXbook for
details.

I wonder if there are video codecs which implement such an algorithm.

Regards,

-- 
  Nicolas George
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