[FFmpeg-devel] [PATCH] RoQ video encoder (take 4)
Fri Jun 15 04:56:50 CEST 2007
On Thu, 14 Jun 2007, Eric Lasota wrote:
> Loren Merritt wrote:
>> Lambda (or equivalently, quantizer) is the only thing that a ratecontrol
>> algorithm can decide. Distortion isn't known until after you encode the
> The old progressive reducer (which got dropped in favor of lambda-based
> rate control) could simultaneously target output size, distortion, or
> lambda. When I modified it to target distortion, it hit within 1% of
> its target every time the target was achievable.
Ok, I was speaking of ffmpeg's generic ratecontrol. A RoQ-specific
algorithm can control other variables.
Then the reason for using lambda as opposed to an a-priori bitrate or
distortion target is that lambda is optimal in the sense of minimizing
total distortion over several frames for any given total size of those
frames. That's only mathematical distortion, it doesn't prove that the
resulting video looks better than a constant distortion encode... but then
the constant distortion encode is also only using mathematical distortion.
And my experiments (which do not include RoQ) indicate that constant
lambda doesn't vary the quality _enough_. That's why qcomp<1 in the
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