This is a greate example of an interactive video. This will allow you to play a piano whilst the host of the video plays a guitar. This is very fun to play with. This works with the host setting some key points in his video, so when you play the piano the video will go to diffrent clips and then will you will hear the sound of his guitar with every key you will click on the piano.
http://www.youtube.com/watch?v=OtcpO4vipNU