Just got back into Joomla and am still loving your editor. I've purchased the Pro to get the ability to add video to an article easily. However, I (well the client!) want to create video as the thumbnail for the articles so I've created a custom field and set it to the JCE Media Browser, but it cannot find MP4 and says they are unsupported? I can however add to articles no problem.
I have solved the problem by creating a text field and adding the URL of the video from media manager to that field, but you know clients are stupid and using the media browser to locate the file would be easier for their simple minds!!