[XviD-devel] GME and Block ME

[Radek Czyz]

Hi everyone,

gruel wrote:
> Currently, I "solve" this by using _two_ block searches, one pre-analysis
> before GME and the ordinary after GME. I can't just use MEAnalysis (for
> B-frame decision) as pre-analysis, because it's too coarse. I need at
> least 16x16 blocks in halfpel resolution, so just ordinary ME, except for
> 4MV. With MEAnalysis this make 3 step of block ME... suboptimal!

> Is anyone interested in a small discussion about how to get rid of this
> double/trippe work? Syskin perhaps?

After one day of thinking, I really didn't come up with anything...
So let me just ask you, how bad MEAnalysis is? I never checked it ;)
How bad would it be to follow it with halfpel refinement? This can
only be done in FrameCodeP, because we don't have halfpel-filtered
pictures available during p/b/i decision. We could also peform the
motion search for all edge macroblocks, because we have edges then (we
ignore all edge MBs during decision, not only because edges are not
available, but also because it could be difficult to find good motion
for them for example in case of camera panning).


Now, differenent stuff:

Has anyone heard of using 'sum of squared DCT coefficients' in place
of SAD/SSE? I tried that, call it holiday-boredom if you wish ;)
It was better then SAD, and at least not worse: 1-3% filesize gain at
almost exactly the same PSNR. Better then SSE. And not _horribly_ slow.


And diffenrent stuff again:

gruel wrote:
> (...) and start writing a trellis quant inbetween?

Yay, trellis quant :-) I was about to ask you what it's all about,
googling for it gave me nothing :(. Anyway, could you please tell me,
briefly, how it works? I understand that it's looking for
optimal bits/distortion, but the question is: what does it do to
change bits/distortion? At first I thought it's changing the quantizer
but no - ffmpeg's file with trellis quant had constant quantizer. So I
thought that it's decreasing, maybe discarding coefficients - that
would decrease number of bits and increase distortion, ok. But again,
no - ffmpeg's file was _larger_ and with much better PSNR...
I have just no idea how is it possible to increase PSNR, or even
increase bits (or both..) during quantization....

Ffmpeg's code was way too criptic for this ;)

Regards,
Radek