Hi All,
I just discovered something… embarrassing. Talking about UE4 under OsX, But I suspect the same for UE4 under Windows.
Once upon a time, I was used to import video just, in fact, importing it 
, as described in the Media Framework Guide. Dragging and dropping, or just selecting it from the file picker etc. At some point this mechanism broke, and right now, if you try doing that with 4.9, 4.10, 4.11 beta, you you will not be able to play a video file any more from the UE4 media player. It will not expose any video or audio track and the play button will be disabled. I interpreted this as a serious bug, breaking all the Media Framework. But yesterday, by chance, I opened a 4.8 scenario of mine, where videos are used, with UE 4.9… and it worked. My mind boggled a little, and then I discovered that, if you PUT YOUR VIDEO FILE IN THE CONTENT/MOVIES FOLDER BEFORE IMPORTING IT, it will work.
Moreover, putting the file there and THEN launching UE4 will automatically import and create a WORKING .uasset file.
I knew it is mandatory to put videos in the /content/movies folder for correctly packing a scenario, but I did not imagine it is mandatory to put them there to make them work at all…
Please, VERIFY THIS BEHAVIOUR and EXPLICITLY STATE IT IN THE MEDIA FRAMEWORK DOCUMENTATION
Thank you again for your IMPRESSIVE work on UE4. I hope this message can be useful for UE4 devs and community.
Later,