This is a great idea in theory, but how do you come up with an immutable hash of a song that a user can enter into the database? Even if you have a recording, m

This is a great idea in theory, but how do you come up with an immutable hash of a song that a user can enter into the database? Even if you have a recording, most music these days is stored in a lossy format. If you have the MP3 version, the Apple AAC version, and some high quality .flac version, they're all going to sound mostly the same, but the underlying data is not even close to identical. How do you hash the audible result, in a reproducable way? I'm not trying to bash on the idea mind, I just think this is an interesting problem and I'm curious if solutions already exist. Surely Shazam and the like have to be doing something in this vein.