Youtube videos stay in full screen but the sound continues?

My TV is connected to my notebook via an HDMI cable. As soon as Youtube videos run in full screen, the picture stays constantly until I move the mouse… As soon as the loading bar / video info disappears then the picture stops.

So if I move my mouse all the time, there's not a single jerk. What can I do? I've been trying on it for two hours.

Only if you see on the TV or even if you only see on the notebook?

The picture just stays on the TV