Not a piano game. IF you want a piano game, try Keyboardmania (though it was cancelled after 3rd mix).
This would be Pop'n Music (He is playing on a pop'n music 7 machine to be exact), and playing Concertare [Classic4] on Hyper with Hi-Speed 4 and Random.
THis video is from quite a few years back, pretty ancient now.
I own the CS version os Pop'n music 8-11, and am getting 12(Iroha) when it comes out in March. Though I don't have 7, so I haven't gotten to play Classic 4 yet, it's a level 41. I can pass everything up to level 39 and a couple 40s.
Pop'n Music is a keysounded music game featuring a large selection of characters and genres of music. When you pick a song notes will begin to fall from the top of the screen towards a red line, there are nine colored buttons roughly the size of your palm, and when the notes (same color as the buttons) gets to the line, you press it to create a sound; continue slapping the buttons to create the music/vocals for the song.
There are currently 16 arcade version of Pop'n music including: Pop'n Music 1-13, Disney's Mix, Animelo, and Animelo 2.
See my signature for more details, though I need to update it since 13(Carnival) was released..
But this should cover everything about this. Hope I didn't over do it. XDD
P.S. Video Google is your firend for tatsujins.
http://video.google.com/videosearch?q=Pop%27n+Music