[FFmpeg-devel] [PATCH] Issue 543, clarification of -bt in docs

Michael Niedermayer michaelni
Sat Jul 26 04:02:33 CEST 2008

On Fri, Jul 25, 2008 at 03:21:44PM -0600, Loren Merritt wrote:
> On Fri, 25 Jul 2008, Jason Garrett-Glaser wrote:
> >> btw, one thing i wanted to ask you since a while already ...
> >> Are you interrested in merging the x264 & lavc ratecontrol code?
> >> The reason why iam asking is that IMHO the current state of it being
> >> "forked" in x264 and being improved there isnt ideal. And that will
> >> become just worse over time as people improve both independantly ...
> >
> > The main problem I see is that x264's ratecontrol code depends heavily
> > on an Xvid-style low-resolution lookahead, especially the VBV code.
> > I'm not familiar enough with LAVC's ratecontrol to know whether LAVC
> > has similar, but if it doesn't, that is a dealbreaker.
> lavc instead runs fullpel motion estimation before ratecontrol. The 
> fullpel sads should be usable for the same purposes. I don't know which 
> is more accurate at predicting complexity.

This isnt correct, we run the complete motion estimation before 1pass
ratecontrol. Prior to the main motion estimation there is an optional
pre motion estimation pass that does pretty much what normal ME does but
bottom to top.

Also both ME passes have fully user configureable comparission functions,
so SAD,SSE,SATD, ... are all there if the RC code has any special preferance.

So i think the lookahead stuff is available, it also would be interresting
to do the RC twice, once after pre ME and then again after real ME that
way the final ME would have a more accurate QP to mix bits & distortion
in 1pass mode. In 2+pass mode the predicted QP is available prior to ME

And last we do have code to guess the best number of b frames by encoding
low resolution frames in estimate_best_b_count() this or some new code
could be used for some farther lookahead if wanted.

What lavc is really lacking is more people working on the encoding stuff,
finetuning it, ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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