There are several threads on this topic in this forum.
Let me guess. You're on a mac with OS 10.11.
For now it seems like they know it's an issue and they're working in a fix. If you can't wait, people who have upgraded their OS (and cleaned their media cache) say it has solved this issue.
I'm going to back-up and upgrade my OS this weekend.
Can you direct me to those threads. thank you.
Unfortunately I just updated my OS as well as cleaned media cache and my MPEG as well as certain MOV files still only read as audio.
I have been searching for a solution for a very long time and have not yet found one