I have shown a Katy Perry song before on my blog, but that's not because she is my favorite singer; it's just that she has very catchy songs. This mash-up is by two famous Youtubers (yes, I used Youtube as a noun) who share their versions of famous pop songs on the video-sharing website - William Ting (a.k.a. Iwillbot) of Seattle, Washington and Tiffany Alvord, from California. Here is Will playing the piano while Tiffany is strumming the guitar and singing Katy Perry's "Firework". Enjoy!
Make sure you start the second video seven seconds in when you play the first video.