Music brainz uses a closed source finger printer. Basically it calculatets one feature vector accross the first 30 seconds of a song and sends it to a central server which assigns it a trm id. The server code is closed, so the finger printing is closed. Also to get proper fingerprinting that performs well (Accross multiple bitrates etc.) you should calculate multiple feature vectors (see the philips paper at http://www.research.philips.com/InformationCenter/Global/FArticleSummary.asp?lNodeId=927 ) . The music brainz song matching performance is pretty poor.

Music brainz is an excellent source for clean meta data, its a shame they dont have a better fingerprinter, I suspect that if they had one we would all be using music brainz ...