You are god amongst men.
Thank you I faced this issue and didn't know what was wrong.
The ffmpeg from the download was built on October of 2012.
The ffmpeg version from the origin site is 2013 and is the latest.
We identified this issue only a Mac dev converter them.... and the webm videos started working.
I used use ffmpeg to do the conversion, after I used it for a while, I found that it can not convert some format and always appeared problem. Then I googled and find Pavtube is recommended by many people and I downloaded it to have a try. The conversion speed and output video quality is pretty good, and the formats it can transfer are very board which make up the disadvantage of ffmpeg.
But for evo videos it can only support non-protection video.
Really? I had a Pavtube license on my old laptop (lost) which I remember it did the protection removing...
If you are having issues with ffmpeg, pease download an updated version of ffmpeg from here:
You will now be able to convert without issue using MVC.