Is that before the user presses play or when it is playing stanxxx ?
OK, I looked at some video’s on my own website and the black borders are actually part of the youtube thumbnail. They are generally (but indeed not always) invisible as background-size is set to cover by LYTE. If you can give an example URL on your site where the problem occurs, I’ll be happy to check there if this applies to your case as well.
I sent you a message with the website’s url in your site. By the way your autoptimize is really good 🙂
I’m afraid the black top and bottom borders are indeed part of the thumbnail, see e.g. https://img.youtube.com/vi/EoutpnHWkVA/hqdefault.jpg, so nothing much you can do there I’m afraid.
