Maybe this will help some? Using the Video Link Above (I think it's the same one anyway, why I posted this link).
I have Win 10. Using IE 11 (current version) the top 2/3 of the video in the post itself is black and the bottom 1/3 shows that part of the video. It's operated this way as long as I can remember.
Using Google Chrome 51 something both worked just fine. (I didn't get the full 51 version due to the auto update.) When I went to check the version of Chrome it updated itself to v52.0.2743.82 m and now the video in the post does not work at all. It starts, shows a darkened picture and then just hangs. The attachment below works just fine. I don't use Chrome a lot so I can't say how it has operated previously.