iMovie 2013 trouble?

So I've recently updated my iMovie, and after getting over all the editing bumps and figuring everything out, my movie won't upload to youtube properly. When exporting, I choose "file" and save. But it always saves as an .mp4 file? So when I upload it to youtube, its just audio and a black screen. I've tried re-exporting numerous times and I still get the same result. Even going into the video properties and changing it to a .mov doesn't help either! It's still a black screen with just the audio. Is there anyway I can change it to an .mov file or something during export? Please help!