Youtube should auto-magically stop any video when you open a new one.

So I had this idea, and I considered, how hard would this actually be to implement?

I mean, I'm not the most technical guy there's but it makes sense to me that you should be able to code that in a way that via cookies you've the session of an user identified, and you're able to auto-pause a video when a new one starts playing.

It's a pain in the ass to have to look among 25 open tabs, and look for the video screwing up that amazing song you've just started to play. I know, I know, they implemented the 'play' favicon, yay for them, but it would just be plain more friendly the solution I propose.

I'm just asking if someone with the skills think it would be very difficult to implement, I know Google has probably 1000 reasons not to do so.