A little reading discovered this:
Youtube has discontinued the embed object type of embed code. they said they were going to do it several years ago and finally did. you need to read the rest of the posts in this topic to find out how to switch over to the iframe embed code for your bbcode.
https://www.phpbb.com/community/viewtop ... p=14501021
Makes my head hurt and eyes glaze over...
EDIT to ADD - More info found and yes, imbeds do still appear on IOS -
It's not a forum issue. It affects all browsers on Mac and Windows OSes because the problem is on YouTube's side. They have broken embedding or streaming to the embedded Flash player. Google is about to do what has been coming for a long time - they will drop support for Adobe Flash this September.
What you need to do is find a proper modern HTML5 video player instead of Adobe Flash. On Safari OSX we've had success with,
http://www.verticalforest.com/youtube5-extension/
Which is installed as an extension. Uninstall or disable Adobe Flash, download the extension linked above. Right click or control click it and choose to open it with Safari.
For Windows and other browsers use Google to search for an HTML5 video extension, plug-in, or whatever terminology that platform uses.
You'll notice that the embedded videos play on iOS because Apple doesn't use Adobe Flash to stream video on iOS.
Here’s the link to this discussion - http://forums.musicplayer.com/ubbthread ... deo_Issues