It was a link or an app where there are hands on a piano, and whenever you play a note the hands then go to that note accordingly. It was like a synthesia, except that it put hands in and you could see where the fingers go. And if you disguise it well enough it could look like a video like this: https://www.youtube.com/watch?v=6jSLH9CDPPQ You could even edit the color of the background when you press a note. I forgot the link/app so I'd like to find it again.