AcoustID is a project providing complete audio identification service, based entirely on open source software.

It that consists of a client library for generating compact fingerprints from audio files, a large crowd-sourced database of audio fingerprints, many of which are linked to the MusicBrainz metadata database using their unique identifiers, and a web service that enables applications to quickly search the fingerprint database.

acoustid.org
Applications
Acoustic Fingerprint – Wikipedia