I actually found that same page and tried that before starting this thread, so I had another go after you said to use this process and I got it working.
I found that I was using the wrong .class, “video” not “vidoewrapper”.
The original video/image was an embedded URL however it appears it must be a link with applicable dimensions in an iframe.
Anyway its now working exactly how I want it to be and across devices. Winning.
I will apply the changes to my live site in due course.