Multi-Core Encoding with VP9 FFmpeg
Thanks for the info about order of options @bodhi.zazen and @LordNeckbeard. Apparently the libvpx encoder is a little more picky about that. When I added -threads option after -c:v libvpx, it visibly uses more cores according to top.
-threads 0 only uses 1 core, -threads 8 uses 2 cores, and -threads 16 uses 4 cores. I've tried using a higher number, but the encoder says more than 16 threads is not recommended, and doesn't use any more CPU. Encoding speed itself is about twice as fast now. Thanks again for the help!