[FFmpeg-user] blotchy encoding on stationary areas

[Matt Zagrabelny]

Greetings ffmpeg folks,

I have been using ffmpeg to encode DVDs to webm files (vp9). Things
look really good in general, however it seems that when the scene is
not changing much, such as a person talking and the camera doesn't
move off of them, then the walls in the scene will get encoded with
very big blotchy squares.

Here are my encoding commands:

ffmpeg -i INPUT.vob -vf yadif -pass 1 -passlogfile first-pass-log-file
-b:v 2M -auto-alt-ref 1 -quality best -minrate 100K -maxrate 16M
-lag-in-frames 16 -keyint_min 0 -g 360 -skip_threshold 0 -qmin 0 -qmax
60 -vcodec libvpx-vp9 -f webm -- - &> /dev/null

ffmpeg -i INPUT.vob -vf yadif -pass 2 -passlogfile first-pass-log-file
-b:v 2M -auto-alt-ref 1 -quality best -minrate 100K -maxrate 16M
-lag-in-frames 16 -keyint_min 0 -g 360 -skip_threshold 0 -qmin 0 -qmax
60 -vcodec libvpx-vp9 -acodec libvorbis -aq 3 OUTPUT.webm

Any suggestions on things to change to get rid of those blotchy areas?

I was thinking of maybe upping the minrate. I know I can try
experimenting with the encoding parameters, but I was hoping for a
little direction in what to perhaps perturb.

Thanks for any help!

-m