'a' for Marshmello - Happier, 's' for Avicii - Levels, 'd' for Noisestorm - Crab Rave [Monstercat Release], 'f' for Ali-A Intro Meme and 'g' for Alan Walker - Faded. If you want to switch the music, click the stop sign first, then click the key for the song you want.
Credit to the creators of the music.
