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

[Corey Hickey]

Nicolas George wrote:
>> 						   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.

Sure, and I suppose, theoretically, there are plenty of other changes
that could be made; however, unless I'm mistaken, x264 doesn't do any of
that, so what I wrote was true for the topic under discussion. Correct
me if I'm wrong. :)

--------------------------------------------------------
for i in 1 3 ; do
  mencoder in.avi -ovc x264 -x264encopts qp=1:pass=$i \
      -o out-$i.avi -frames 320
done
--------------------------------------------------------

$ diff out-1.avi out-2.avi


> 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.

I don't know of any (which doesn't mean much), but I would be interested
to see how much of a difference it makes.

-Corey