Get audio features for ONE track — BPM, musical key (name + Camelot + Open Key),
energy, danceability, valence, acousticness, instrumentalness, liveness, speechiness,
loudness, mood, mood_vector, genre, time signature, duration and more.
This is the drop-in replacement for Spotify's deprecated /audio-features endpoint.
Provide AT LEAST ONE identifier — if you know several, send them all rather than
choosing; they resolve by precedence (`track` > `isrc` > `mbid` > `spotify_id`) and
the rest are ignored:
- `track` (optionally with `artist`) — e.g. track="Blinding Lights", artist="The Weeknd".
- `isrc` — e.g. "USUM71900001".
- `mbid` — a MusicBrainz recording UUID.
- `spotify_id` — a Spotify track ID, URI, or URL (resolves only the <1% of the
catalog already mapped to a Spotify ID; prefer `track`/`isrc` for full coverage).
Returns a JSON object of features. Some feature fields may be null for tracks resolved
via the fallback catalogs (only audio-derived values are present for fully analysed
tracks). If a track name is not yet in the catalog, the API holds the request during the
on-demand ingest and usually returns the fully analysed track inline in this same call;
only if the ingest runs long does it fall back to a queued response you can re-poll
shortly (~15s). If the track turns out not to be on any streaming source we can analyse,
you get a definitive not-found instead — that verdict is terminal for ~7 days, so don't
retry it. If you only have a fuzzy or partial name, call search_catalog first to
find the exact track.