title: FFMpeg Compress WebM - VP9 with alpha channel
body: <p>I'm looking for a way compress a quicktime .mov in animation format with alpha to VP9. I've tried the following:</p>
  
  <pre><code>ffmpeg -i Elephant_01.mov -vcodec libvpx-vp9 -pix_fmt yuva444p output3.webm
  </code></pre>
  
  <p>but I get an <code>incompatible pixel format...</code> error.</p>
  
  <p>any suggestions, as far as I can tell VP9 -should- support the yuva444p format. Or is there another tool that works?</p>