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AcoustID fingerprints

AcoustID identifies recordings from the sound of your files. OpenTag computes a fingerprint locally, asks AcoustID for matches, then retrieves the chosen release's metadata and artwork from MusicBrainz.

Set up fingerprinting

OpenTag includes Chromaprint and its audio decoder libraries. Install OpenTag normally: no separate fpcalc or ffmpeg program is required. Fingerprinting runs on your device and reads the selected audio without changing its tags.

  1. Add the album's audio files to OpenTag. On Android, choose documents with the system picker so OpenTag has permission to read them.
  2. Open Tag Sources → API keys…. If this build has no AcoustID key, add your application's key using the registration address shown there.
  3. Select the files to identify. Files need readable, supported audio; an encrypted or damaged file cannot be identified just because its tags load.

Advanced desktop users can optionally choose a different producer in Options → Tag Sources → Online services → Optional fpcalc override (desktop). Enter a full executable path, without a shell command or extra arguments. Leave it empty to use the built-in libraries. Old automatic fpcalc settings also use the built-in default. Mobile builds always use the built-in producer.

What happens during fingerprinting

OpenTag decodes up to the first two minutes of each file to calculate its fingerprint and sends the fingerprint with the full file duration. The reported container duration can differ slightly from the audible duration. It does not upload your audio. Processing a long file therefore does not require fingerprinting the entire recording.

Cancel stops the search and asks local decoding to stop. The search also has a two-minute time budget for each file. A blocked file read or decoder can take longer to return; OpenTag allows only one built-in fingerprint worker at a time and asks you to retry if the previous worker is still stopping. The optional external producer has its own process timeout.

Identify and review

  1. Select the album's files and choose Tag Sources → AcoustID (fingerprints)….
  2. Select Search. OpenTag fingerprints each file and ranks releases by the number of selected files matched, then match score.
  3. Select the correct release and choose Next. Compare the edition, track list, matches and artwork, then save.

Identified files are paired with their matched MusicBrainz recordings, including across discs. If files have overlapping candidate recordings, OpenTag reassigns compatible pairs when necessary to keep the greatest number of compatible fingerprint assignments. A direct free track keeps earlier assignments stable; this does not globally optimize match scores. Auto-match, Selection order and Suggest sorting arrange remaining files without replacing those fingerprint pairs. You can still move files manually; inspect the resulting assignments.

ACOUSTID_ID is offered per file only when that file was identified as the recording of its assigned track. Moving it onto another recording does not copy another file's AcoustID. If only ACOUSTID_ID is checked and no ID applies or cover is selected, the file is skipped.

Limits and privacy

A match identifies a recording, not necessarily your exact edition. Several releases can contain it, so the highest-ranked result still needs review. Files without a usable match do not gain an inferred AcoustID.

OpenTag sends fingerprints and durations, not audio files. It performs lookups only and does not submit new fingerprints. AcoustID requests are spaced about 350 milliseconds apart; MusicBrainz lookups use a separate spacing of about 1.1 seconds. Local fingerprinting adds to the time needed.