Some parameter tuning included.

lowres (q, 30 frames, speed 1):
-1.243% av PSNR, -2.337% ov PSNR, +0.577% SSIM

lowres (vbr, 30 frames, speed 1):
-0.327% av PSNR, -1.007% ov PSNR, +0.182% SSIM

A few videos become a lot worse in SSIM, which needs to be
investigated. But PSNR-wise the patch seems pretty good.

Change-Id: I17c8d812c96ee49ddae7d3959a459aa3ffcea208