This sounds like an acoustic fingerprint, such as AcoustID[0]. I think AcoustIDs and XSPF[1] would be a good combination for shared playlists. It's a shame that development stopped on the Tomahawk music player[2], it would have been an ideal platform for shared playlists like this.

[0] https://musicbrainz.org/doc/AcoustID

[1] https://en.wikipedia.org/wiki/XML_Shareable_Playlist_Format

[2] https://github.com/tomahawk-player/tomahawk