chrome extension that pops a message box on every youtube video

I need a google chrome extension that pops a message whenever a video is played on youtube. The message box should pop on EVERY video play. I.e, when the page first loads (easy already done that), but also when the user changes a movie by clicking one of the "related videos" buttons (a bit harder, "youtube" does not reload page on every video change, but I found a way). I already know how to detect a new video on "normal view" but if could not detect that a new movie is played when the user is in full screen mode. This is where I need your help.