Adjust the motion decay component to account for image size.
This has very little impact for smaller image sizes.
Average bdrate results for our HD test sets:-
Hdres set: opsnr +0,92%, Fast SSIM +1.6%
Netflix hd set: opsnr + 1.5%, Fast SSIM +3.1%
There are a couple of notable -ve clips such as cyclist and sunflower
which seem to be better with a shorter interval but also a few very big
wins such as Jets >12% psnr 22% Fast SSIM and from the Netflix
Netflix set PierSeaside 9.7% psnr and 18.2% Fast SSIM.
Change-Id: Ie43aaedaa74331ed83d624a13548094ac64fed9e
81d1e7bf28