title: ffmpeg unable to find encoder libvpx
body: <p>when i run </p>
  
  <pre><code>ffmpeg -y -i test.mov -threads 8 -f webm -aspect 16:9 -vcodec libvpx -deinterlace -g 120 -level 216 -profile 0 -qmax 42 -qmin 10 -rc_buf_aggressivity 0.95 -vb 2M -acodec libvorbis -aq 90 -ac 2 OUTPUT_FILE.webm
  </code></pre>
  
  <p>it returns an error saying <code>Unknown encoder 'libvpx'</code></p>
  
  <p>I installed libvpx, libvorbis, libogg, and ffmpeg all via macports</p>