I love that you support webm video uploads, however there is a glitch (not your fault).
When browsers (like Chrome) create webm files, they set the frame rate to 1000fps, which of course is silly. So when i go to upload a 3 second Chrome generated webm file, your site reports an error that the video exceeds 3min.
The solution is to explicitly specify a fps of 24 when converting the upload (via ffmpeg, online-convert, etc).
Trust me on this one :)