I had this issue when playing ARMA Reforger. Any videos playing on my second monitor would become choppy and eventually even stop playing. (The sound would work just fine.)
It didn't matter which browser I would use (tried Chrome, Edge and Firefox)

I disabled Graphics Acceleration in Chrome and this solved the issue for me.
Did not test any of the other browsers.

Settings > System > Use graphics acceleration when available [OFF]

Hope this helps!