[Cin] Suggestion: improve setting for VP9 webm

[Andrea paz]

I compared the old preset (1920*1080; 24-25-30fps) with the new one
you proposed. I've Ryzen 3700X and 32 GB RAM.

Old preset:

** rendered 1043 frames in 50.496 secs, 20.655 fps, size 6.6 MiB (CPU 20 - 23%)

New  preset with b=0 and row-mt=1:

** rendered 1043 frames in 64.259 secs, 16.231 fps, size 19.4 (CPU 50 - 70%)

The difference in fps, despite the increased CPU usage, I think is
explained by the higher quality achieved with your preset.
The "threads=..." option should be used in conjunction with
"token-parts=3," but I don't see much difference in results.
The option "tile-columns=..." should be used in conjunction with
"frame-parallel=1," but again I don't notice any difference...

In my tests I find no difference using "Use HW device" in "none";
"vaapi" or "vdpau", I think it would take special presets.

In general I find VP9 slow, heavy and not efficient on my CinGG (I
have not tried ffmpeg from command line due to lack of time).