iphone screen goes gray while watching videos

so whenever im watching a video on yt or a pirated movie on chrome , every couple minutes the screen with quickly turn gray and then lighten back up to how it was .its not the screen turning off due to inactivity ive already tested , and its not auto brightness bc it happens whether thats on or off .

also its NOT like the brightness is changing , its like someone fills my screen with flat gray color and then lowers the opacity until its gone . i have an iphone se 2nd gen