WIP
VP9 encode is very very slow ?
Yes and no. Unlike x265 use all core to speed up encode time, the low threaded libvpx-vp9 use for me 4 core of my Ryzen 3900X. Encode 4 video in the same time -> x4 "boost".
Force dynamic bitrate with b:v 0
Set quality level with -crf <quality level> is a integer (0 to 63)
libvpx use -deadline and ffmpeg -quality need to be set to good.