[x265] Custom LowRes scale

[Steve Borho]

On 07/22, Nicolas Morey-Chaisemartin wrote:
> 
> On 07/21/2014 07:11 PM, Steve Borho wrote:
> >Interesting. I imagine much 4k content would work decently well even
> >with further downscaling of the lookahead pictures.
> >
> >The lowres motion vectors are used in weight analysis as well, so that
> >file would need to be updated.

> I'll have a look at it. It doesn't semm as straight forward as the
> other files though.

it is slightly more complicated; you'll want to scale up the block sizes
used for motion-compensated weight analysis - up to 32x32 or 64x64 based
on how much further you downscale the lowres in lookahead.

> While we're talking about lowres MV: from what I could gather they are
> not used during the motionSearch on the full res picture.  As a lot of
> time is spent finding those, whouldn't it be useful to add them as
> candidate in the fullres search?

This has been on my TODO list for ages; a couple of people have claimed
they've tried it and it hasn't helped as much as you might think.  But I
haven't had a working patch in hand to verify it.

The AMVP fixup after motion search, where we get to go shopping for a
better MVP after the search, often makes extra motion candidates
superfluous.

-- 
Steve Borho