Re[2]: [XviD-devel] Other clip with Bframes, quality vs size

[Radoslaw 'sysKin' Czyz]

Monday, August 19, Christoph wrote:

> So there is another plot, where not max_bframes gets different colors, but
> bquant_ratio (Dogma-bquantratio.png). Here the colors mean:

> green: bquant_ratio = 100    result: always worse then non-bframes
> blue:  bquant_ratio = 150    result: always better than non-bframes
> purple:bquant_ratio = 200    result: even better in some cases
> turquoise:    ratio = 250    result: best, in many cases (!)

I guess you used my code. So, I have a question: did you alter
SKIP-threshold for B-frames? I have no idea how big this threshold
should be. I set it to 100 at the beginning and didn't see any
difference. To be safe, I decreased it to 70 - similar threshold for
P-frames is only 10 (well not really, it's for initial decision only).

As the skip-decision is : SAD < Quant * Threshold ,

possibly good results for high quant simply mean that this threshold
should be higher. I myself encoded a scene with Threshold = 180 and it
looked still the same to me (and the sizes of B-frames were below 500
bytes at quant 4 & resolution 640x400).

Do you have a working PSNR-computing thingy for B-frames? Do you think
you could send it to me?

I tested b-frames with anime a bit. The (subjective) results are:
When there is a scene with only camera panning (common in animation) -
filesize is 25% smaller *and* 'visiual quality' is higher - there is
no visible static noise on smooth background, while it's quite visible
with p-frames only. I definitely like it.
For other scenes it was good, too. But not that good.

> So, what parameters to choose for an arbitrary file?
> I don't have the faintest idea...

Dynamic P/B decision sounds great. However, I have absolutely no idea
how would that work. Do you have some ideas? Or papers about it?

Radek

PS
@Milan: if you are here, I'll use this mail to ask you: When I tested
B-frames I discovered that ffdshow (downloaded ~5 days ago) shows some
artifacts. They were gone with xvid's decoder and divx5 decoder. Do
you know about it or should I investigate more and send you full
report? (this might be a big in xvid, too).