This issue is caused by a security setting in IE which blocks "active" iframe content (it considers video player "active content"). It's potentially a bad idea to run another site in an iframe, although it is generally safe - it is possibly an XSS security risk. We would normally trust "big G" not to steal our cookies (used for login), right? It's probably not going to happen. By default on modern browsers they should not allow cookies to pass through an iframe to another domain (like youtube).. but its generally a safe practice in modern times to use an HTML "video" tag instead of an iframe....
that being said, this 'blackout video' problem can also be prevented if you stop IE rendering HTML in "Compatibility Mode".
It's possible to disable "Compatibility Mode" in the browser settings. It's also possible to disable the iframe security feature, but let's not go there at the moment.
I did add an HTTP response header which _should_ tell Internet Explorer to NOT do "Compatibility Mode" but i need to test it to see if it works right.
Code:
# HEAD -e http://dr1.com/forums/showthread.php/172219-OK-I-m-bored/page4
200 OK
Cache-Control: private, max-age=0
Connection: close
Date: Tue, 19 Jun 2018 16:03:17 GMT
Pragma: private
Server: cloudflare
Vary: User-Agent
Content-Type: text/html; charset=UTF-8
Expires: Tue, 19 Jun 2018 16:09:02 GMT
X-Powered-By: PHP/5.5.38
X-UA-Compatible: IE=Edge
The forum software is also putting "IE=8" in **** tag the layout, I will track that down and change it as well.
Hopefully this will solve the video issue, without asking the end-user to change their settings.