Here are a couple guides for those who may want to try making some:
gist.github.com/ndarville/10010916trac.ffmpeg.org/wiki/vpxEncodingGuideI use a .bat file that basically looks like this:
ffmpeg -i %1 -c:v libvpx -b:v 3M -crf 4 -an -ss 00:00:0.000 -to 00:00:00.000 -vf scale=640:-1 %1.webm
pause
Onto which I drop the .mkv file (must be in the same folder as the .bat). The -b:v #M and -crf # are the main values to tweak to get an appropriate file size.
Feel free to post any you may have stolen from /a/ or whatever, as well.