Music

There've been a few YouTube channels over the years that do videos almost exactly like this, using clips from movies/TV to fill in the lyrics to a famous song.

The scripts for most movies are available online, so they'll just search the lyrics line-by-line for a hit, then go dig up the clip from that movie where they said the words. The rest is just manually cutting and positioning all the clips along a timeline, scooching each clip frame-by-frame until the spoken lines sync up with the backing music.

The hardest part would seem to be the process of gathering the movie clips, as you'd have to source each movie somehow. And also navigating the copyright minefield that comes with using clips from hundreds of different IPs.