>>889042ffmpeg -i "input filename.mp4" -c:v libvpx -crf 20 -b:v 500K -c:a libvorbis "output filename.webm"
-crf sets quality, lower is better but higher filesize. range is 4 (complete waste on the blocky fucking mess that vp8 is) to 63
-b:v sets bitrate, use the original bitrate minus approx. 100K because libvpx tends to overshoot by roughly that amount
libvorbis has further options but i wouldn't bother because the defaults are good enough
