[XviD-devel] Subpelrefine_Fast

[Radek Czyz]

Hi everyone.

I've been looking at new Subpelrefine_Fast() and I have some
questions. Isibaar, I hope you'll find time to answer them :)

First - do you think the idea will be useful for halfpel-refinement?
It looks like halfpel-ready, but you only use it for qpel.
The way I see it, the total number of checks will actually increase
for halfpel... Am I wrong?

Second - a bug? You seem to check 8 halfpel positions first, to find
the "second best" vector among them. Makes sense but...
    second_best = *data->currentMV;
As long as data->qpel_precision is set (and it is), CheckCandidates
will not change data->currentMV, but data->currentQMV instead.

As a result, it just can't work correctly - or I missed something ;)


The _fast idea is very good, and will be even more useful for VHQ
refinement and b-frame refinement. To implement them, I plan to change
it a bit. There will only be one CheckCandate, but the information
about "second best" etc will only be stored in memory if
qpel_precision is active. Should work as expected, and not be too
slow.
I'll combine it with halfpixel refinement to save some extra halfpixel
checkcandidates (from 3 to 8).

BTW I kinda fear about the complexity of CheckCandidates... On
average, CheckCandidate16 takes about 94 cpu cycles. That doesn't
include functions it calls (like sad16v). Do you think it's slow?


Radek