After I learned how it roughly works, it seems no longer like witchcraft, but it is still impressive.
The remaining thing I don't understand now is how the heck they managed to negotiate the license for all the songs they have in the database. A friend of mine had a major website for lyrics, and he got some legal trouble from the record companies. When he tried to buy a license to display the lyrics, after some back and forth, they basically said they're not interested in licensing. This was in the early 2000s before streaming took off. Since that time I have the impression that often legal and social problems are much harder to solve than technological ones.
They are likely able to show that the DB is comprised of simply the fingerprints, and not the full songs - thus they wouldnt be able to "use" the DB to profit from play-back of the songs it can identify.
The remaining thing I don't understand now is how the heck they managed to negotiate the license for all the songs they have in the database. A friend of mine had a major website for lyrics, and he got some legal trouble from the record companies. When he tried to buy a license to display the lyrics, after some back and forth, they basically said they're not interested in licensing. This was in the early 2000s before streaming took off. Since that time I have the impression that often legal and social problems are much harder to solve than technological ones.