How PUIDs Work
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Music Analysis vs Fingerprinting
There are two processes that AmpliFIND makes available through its MusicDNS service: Music Analysis and audio fingerprinting. Finally there are the PUIDs which are just IDs, not fingerprints.
In summary:
Music Analysis is:
- proprietary closed source AmpliFIND "stuff" done only to generate a new PUID
- able to be done only by the proprietary genpuid and MusicIP Mixer tools
- based on analyzing large amounts of a source track
- executed server-side in MusicDNS servers, taking up to 24-hours
- has a new PUID as its output
- only has to be done once for each semantically identical audio file
Audio Fingerprinting is:
- based on taking small samples of a track's contents
- designed to be used to locate/query the MusicDNS service for an existing PUID
- will only successfully find a PUID for tracks where someone else has earlier done Music Analysis
- able to be done by Picard, genpuid, MusicIP Mixer and other tools based around libofa
- open source, but requires a server query to match to a PUID
Music Analysis in detail
Before a PUID is available for MusicBrainz or Picard to use, Music Analysis must have been performed on a track. MusicAnalysis uses up to 10 minutes of the track and examines all sorts of things. This is the secret sauce that makes MusicIP tick, and that allows the MusicIP mixer (aka MusicMagic Mixer or MMM) to generate playlists of similar music. This is never going to be open sourced. Music analysis takes a while (about 80% of the file's playing time).
In order to generate a new PUID, you must analyze a track fully. Currently you have to use either the MusicIP mixer or MusicIP's genpuid command-line utility in order to do this. The result of this analysis is submitted to the MusicDNS service and is used by the MusicDNS server to do fuzzy matching. This data is closed source, patented, and even secret (the closed source apps send the data to a closed source server, and it never sees the light of the public). The only thing that gets public is the Portable Unique IDentifier (PUID), which is a 128-bit ID of the respective analysis data on the MusicDNS server.
There is a 24 hour latency on the MusicIP side for new PUIDs to become available. This is an artifact of the server architecture, which is optimized to do large numbers of lookups efficiently. (In practice, the latency is currently less than 12 hours.) This should disappear at some point in the future, but not until the MusicIP server architecture is updated.
MusicAnalysis cannot be integrated into the PicardTagger, because the process is closed source and Picard is GPLed.
Audio Fingerprinting and PUIDs in detail
Fingerprinting is a much smaller process - it analyzes about 2 minutes of the track using the open source libofa library to calculate an AudioFingerprint and should take 2-3 seconds per regular-sized track.
With this fingerprint data, you can only do a "lookup" on the MusicDNS web-service, which returns a PUID if a sufficiently close match has been submitted via the MusicAnalysis described above. If MusicAnalysis has not been performed on the track by someone else; no PUID will be found for the track. MusicIP provides free fingerprint lookup services for official MusicBrainz projects and other open source projects.
Note that the PUID is just an arbitrary ID and has no relation to the fingerprint data (except for its relation within the MusicDNS server). This means you cannot generate a new PUID to insert into the database from the fingerprinting process. A new PUID can only be allocated by MusicDNS as a result of the detailed MusicAnalysis process. For the technically minded, consider a fingerprint to be a key that can be used to query for a value, being the PUID.