This is How to Make a Song Mashup

Have you ever wondered how in the world audio artists like Bill McClintock and DJ Cummerbund make those marvelous song mashups out of very different songs from different genres? The secret is the chord progression. If two songs have the same chord progression, the melody can be transferred from one to another. Oh, they might be played in slightly different keys or have a different tempo, but those can be manipulated by computer, and if they are close enough to start with no one will notice. Besides, most songs are in the simpler keys anyway.

Pianist David Bennett illustrates how this is done by swapping the music and lyrics of disparate songs that have the same chord progression. Even if you don't know anything about music theory and don't care about chord progressions, you'll enjoy a video in which Michael Jackson sings over a U2 melody, and Celine Dion croons over a Phil Collins tune. The previous video he mentions is here.  There's a 30-second ad at 5:35.