[x264-devel] Default value for the --scenecut option causes heavy undesirable flood of I slices in active scenes

[Vladimir Chernyshov]

Well, that's simple - B-frames are coded with higher QP, and take less 
space than either I or P frames. You can check the total bitrate reading 
from the statistics in my posts.

On the other hand, I-frames are coded with much lower QP in the hope 
they can be useful for predicting subsequent frames.

Thus with plenty of I- and P- frames the average quality is boosted, 
which is against the idea of CQP VBR mode, and not desirable in 
highly-active scenes.

regards,
Vladimir


Jason Garrett-Glaser wrote:
> On Sun, Nov 2, 2008 at 1:48 AM, Vladimir Chernyshov <vchernys at welho.com> wrote:
>> I tried --pre-cut. It worked only marginally better. It still inserted
>> few extra scene cuts through the scene, and has suppressed all B-frames,
>> which are highly desirable in the highly-active scene to keep bitrate down.
> 
> How does it "keep bitrate down" to use B-frames when they are
> counterproductive?  Given the percentage of I-blocks in the scene, I
> severely doubt that the B-frames are "highly desirable", considering
> the enormous size of the coding prefix used for I-blocks, especially
> when using CAVLC.
> 
> Dark Shikari
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