@speedylunar Try the steps in https://forums.opera.com/topic/23068/instructions-on-posting-about-problems-in-opera-for-computers
It doesn't seem to be happening here. Check also your video and monitor settings.
Just updated to Opera stable 54.0.2952.46 today. Did this after Ubuntu 16.04 upgraded to chromium-codecs-ffmpeg-ex 67.0.3396.62 and all videos seem to play well on Opera v54.
However one strange thing that remains is, on some sites videos will not play when using New Private Window. I get out of New Private Window and then those same videos now play fine. Go back into New Private Window and again those videos refuse to play, saying Flash needs to be enabled! Try to enable Flash but nothing happens. Any idea why this happens?
This feature is horrible, as someone that can have hundreds of tabs open. I've considered switching browsers a dozen times because of this stupid idea. Make it toggleable already, I'm quickly losing patience.