Implement sonicSimilarity extension with real audio feature analysis

Adds internal/audiofeatures: decodes each scanned song to PCM via
ffmpeg and computes actual measured characteristics — tempo (via
autocorrelation of the frame energy envelope, left unset rather than
guessed when a clip is too short to contain a beat), an approximate
loudness figure, spectral centroid/rolloff and zero-crossing rate (via
a hand-written FFT), and a 12-bin chroma vector used both for a
Krumhansl-Kessler key estimate and as similarity-index input. No
external DSP/ML dependency.

The scanner now runs this analysis after indexing each song (as part
of the already-background scan, not on any request path) and stores
results in the existing audio_features table via the new
database.UpsertAudioFeatures/GetAudioFeatures/ListAllAudioFeatures.

internal/similarity is a small in-process nearest-neighbor index:
z-score normalizes each feature dimension across the analyzed library
and answers Nearest (ranked real distances) and Path (a feature-space
straight-line walk from one track to another, hopping to the closest
not-yet-used real song at each step — never a fabricated intermediate
track).

getSonicSimilarTracks and findSonicPath expose these through the
standard sonicMatch response, converting distance to a normalized
(0,1] similarity score. A song that hasn't been analyzed yet is simply
absent from results rather than faked.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014r98AtcBbevpscWLsfwVvv

This commit is contained in:

owen

2026-08-23 08:30:20 -05:00

co-authored by

Claude Sonnet 5

parent 6fb46a989e

commit b6acd63c2d

13 changed files with 1486 additions and 4 deletions

									
										internal/subsonic/opensubsonic_core_test.go
									
		+1
		-1
	
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				@@ -55,7 +55,7 @@ func TestGetOpenSubsonicExtensions(t *testing.T) {

					// set once Phase 3 is done.

					for _, want := range []string{

						"apiKeyAuthentication", "formPost", "getPodcastEpisode", "topSongsByArtistId", "transcodeOffset",

						"indexBasedQueue", "playbackReport", "songLyrics", "transcoding",

						"indexBasedQueue", "playbackReport", "songLyrics", "transcoding", "sonicSimilarity",

					} {

						if !names[want] {

							t.Errorf("extension %q not advertised: %v", want, names)