Two identities per track, because they answer different questions:
- audio_stream_sha256: SHA-256 of the ENCODED audio packets
(ffmpeg -map 0:a -c:a copy -f hash). Equal means identical audio
whatever the tags say. Measured against the #3885 pair: the two WWW
files hash identically here and differently as whole files. Packets
rather than decoded samples, so an ffmpeg upgrade cannot silently
change every stored hash, and nothing is decoded.
- chromaprint: fpcalc -raw -signed. The same recording at another
bitrate or codec, for the acoustic tier.
fpcalc ships in the image (libchromaprint-tools); shelled out because
CGO_ENABLED=0 rules out bindings.
Stored in a track_fingerprints table rather than on tracks: eight
queries read tracks with SELECT *, including album pages, search and
the Subsonic surface, and a ~4 KB array there would be de-TOASTed on
every one of them.
The scan fingerprints only bytes it has not seen (a new path, or mtime
past the row's). A tag-repair pass leaves fingerprints alone, and
unchanged files with no fingerprint are the backfill's job (#3908).
Folding that into the skip check would re-decode the whole library on
the first scan after upgrade and push a sync change per track.
A failure that says nothing about the file (timeout, cancelled scan,
tool not installed) is never stored, and on changed bytes it removes
the old row. A tool that rejects the file stores NULL at the current
version, so the backfill does not retry it every boot.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SQ31KQpYbStyK5y58UmPLH
