[XviD-devel] Global Motion Compensation
Christoph Lampert
xvid-devel@xvid.org
Thu, 24 Oct 2002 13:27:57 +0200 (CEST)
On Thu, 24 Oct 2002, Michael Niedermayer wrote:
> encoding is not more difficult than decoding IMHO, as the motion estimation is
> allready done, we just need to analyse it to find good warp points ...
For translational: yes. For the others: No, ordinary motion vectors are
by far not exact enough to find subpictional zoom/pan etc. parameters.
Most likely that's the reason why DivX5 does translations only.
> > Maybe more tweaks are possible for fast decoding, too.
> > (pre calculated tables or something...)
> hmm, i doubt it a bit
Me, too... but who knows ;-) Is GMC decoding MMX/XMMed? Maybe it's
3dnow/SSE/SSE2able?
> > The only argument would be that you don't gain anything from GMC, which
> > may be true for most videos, but sometimes it seems to help during
> > zoom/pan, so I'll at least have a look.
> hmm, its allways a question of complexity vs. compression gain, never just
> compression alone, or why dont we all do full ME search?
Okay, partly agreed. A slow feature should only be enabled if there is
a sufficient gain, but what "sufficient" means depends on the application.
Full search ME is an extreme example of slowdown at hardly any
better ME results (than PMVfast/EPZS) in all sequences I know.
If GMC gives 1dB gain in 5% of sequences and nothing in 95%, it's somehow
a different story... those things can be tested and the feature only
actived when needed.
gruel