Local Library Skill

Reference for local media library: scanning, persistence, NAS responsiveness, and display-layer queries.

Key Files

Area	File
DB layer	Data/Models/MediaLibraryStore.swift
Library model + scan	Data/Models/MediaLibrary.swift
Track model	Data/Models/Track.swift
File discovery	Utilities/LocalFileDiscovery.swift
Audio engine (NAS paths)	Audio/AudioEngine.swift
Waveform (cue-sheet)	Waveform/BaseWaveformView.swift
Play history (Data tab)	Windows/ModernStats/PlayHistoryStore.swift, Windows/ModernStats/PlayHistoryAgent.swift, Windows/ModernStats/StatsContentView.swift

Database Schema

Library: MediaLibraryStore (SQLite via the SQLite.swift package). Replaced legacy library.json.

PRAGMA settings

• journal_mode=WAL — readers and writers proceed concurrently; prevents main-thread SELECT from blocking background INSERT during import.
• synchronous=NORMAL — safe with WAL, reduces fsync overhead during bulk import.
• busyTimeout = 5s — prevents hard failure on background/main thread contention.

Schema version (PRAGMA user_version)

• v0 → v6: fresh install creates all tables, runs migrateToV5 then migrateToV6.
• v1 → v2: migration adds idx_tracks_artist_expr expression index (see Indexes below).
• v2 → v3: migration adds track_artists table with ON DELETE CASCADE FK (see Tables below).
• v3 → v4: migration adds extended metadata columns (composer, comment, grouping, bpm, musical_key, isrc, copyright, musicbrainz_recording_id, musicbrainz_release_id, discogs_*, artwork_url) via ALTER TABLE … ADD COLUMN.
• v4 → v5: migration adds play_events table and indexes (see Tables below).
• v5 → v6: migration adds content_type column to play_events (TEXT, nullable); backfills 'radio' for source=radio rows, 'music' for everything else.
• v6 → v7: migration adds output_device column to play_events (TEXT, nullable). Records the active CoreAudio output device name, or the cast target name (Chromecast/Sonos/DLNA device) when a cast session is active. NULL for legacy rows. Supplied via CastManager.currentPlaybackDeviceName at call sites in AudioEngine and VideoPlayerWindowController.
• v7 → v8: migration adds library_playlists table (see Tables below) for on-disk .m3u/.pls/.m3u8 files surfaced in the Plists tab. Both paths required: migrateToV8 issues CREATE TABLE IF NOT EXISTS for existing DBs, and createTablesIfNeeded creates it on fresh installs — createTablesIfNeeded only runs at user_version == 0, so a fresh-path-only addition would leave every existing library without the table. The fresh path falls through the sequential if currentVersion == N blocks; each block now sets currentVersion = N so V8 is reached from both fresh (v0→…→8) and upgrade (v6/v7→8) paths.

Tables

library_tracks

Column	Type	Notes
id	TEXT PK	UUID string
url	TEXT UNIQUE	Absolute file path
title	TEXT
artist	TEXT?
album	TEXT?
album_artist	TEXT?
genre	TEXT?
year	INT?
track_number	INT?
disc_number	INT?
duration	REAL	Seconds
bitrate	INT?	kbps
sample_rate	INT?	Hz
channels	INT?
file_size	INT	Bytes
date_added	REAL	Unix timestamp
last_played	REAL?	Unix timestamp
play_count	INT	Not nullable; defaults to 0
rating	INT?	0–10 scale
scan_file_size	INT?	Snapshot at last scan
scan_mod_date	REAL?	Snapshot at last scan

Indexes on library_tracks

• idx_tracks_artist (album_artist, artist) — sort/filter by artist.
• idx_tracks_artist_expr (coalesce(album_artist, artist, 'Unknown Artist')) — expression index required for artistNames GROUP BY and albumsForArtist/albumsForArtistsBatch WHERE clauses. Without this, those queries do full table scans (caused minutes-long UI freezes on 60k-track libraries). Must not be removed.
• idx_tracks_album (album), idx_tracks_genre (genre), idx_tracks_year (year).

library_movies

id, url (UNIQUE), title, year, duration, file_size, date_added, scan_file_size, scan_mod_date.

library_episodes

id, url (UNIQUE), title, show_title, season_number, episode_number, duration, file_size, date_added, scan_file_size, scan_mod_date. Index: idx_episodes_show (show_title, season_number).

library_watch_folders

url (PK), added_at.

library_playlists (added v8)

id (TEXT PK, UUID string), url (TEXT UNIQUE, the .m3u/.pls/.m3u8 file path — the stable natural key), title (filename without extension), file_size (INT), date_added (REAL), scan_file_size (INT?), scan_mod_date (REAL?). Index: idx_playlists_title (title). Stores only the playlist file location — track contents are NOT persisted; they are parsed lazily on expand in the browser. CRUD: upsertPlaylists, allPlaylists, deletePlaylistsByPath, deleteAllPlaylists (mirrors the track methods). upsertPlaylistInternal reuses an existing row's id when the url already exists (looks it up via connection.pluck — not scalar, which force-unwraps nil and crashes on no-match), so the PK and in-memory/expand state stay stable across rescans. All in-memory and UI state keys on the file path, never on id.

library_album_ratings / library_artist_ratings

album_id/artist_id (PK), rating.

track_artists (added v3)

Column	Type	Notes
track_url	TEXT	FK → library_tracks(url) ON DELETE CASCADE
artist_name	TEXT
role	TEXT	'primary', 'featured', or 'album_artist'
PK: (track_url, artist_name, role). Indexes: idx_track_artists_name, idx_track_artists_url.

play_events (added v5, extended v6)

Column	Type	Notes
id	INTEGER PK	AUTOINCREMENT
track_id	TEXT?	Library UUID if local track
track_url	TEXT?	File path if local track
event_title	TEXT?
event_artist	TEXT?
event_album	TEXT?
event_genre	TEXT?
played_at	REAL	Unix timestamp, NOT NULL
duration_listened	REAL	Seconds, NOT NULL, default 0
source	TEXT	'local', 'plex', 'subsonic', 'jellyfin', 'emby', or 'radio'
skipped	INTEGER	0/1, NOT NULL, default 0
content_type	TEXT?	Added v6. Values: 'music', 'movie', 'tv', 'radio', 'video'. NULL treated as 'music' in queries. Derived from Track.playHistoryContentType; video playback records from VideoPlayerWindowController set this explicitly via beginPlaybackAnalyticsSession(contentType:).
output_device	TEXT?	Added v7. Name of active audio output device (CoreAudio) or cast target device. NULL for legacy rows.
Indexes: idx_play_events_played_at, idx_play_events_track_id, idx_play_events_source_time.
Queried by PlayHistoryStore (in Windows/ModernStats/) to power the Data tab in both the modern Library Browser and the classic PlexBrowserView.

insertPlayEvent signature (in MediaLibraryStore): takes contentType: String = "music" and outputDevice: String? = nil as trailing parameters — both default so all existing callers work unchanged. Pass track.playHistoryContentType and CastManager.currentPlaybackDeviceName at call sites. Internet radio sessions pass outputDevice from CastManager.currentPlaybackDeviceName at the time the event is recorded.

Key API Methods (MediaLibraryStore)

• Paginated queries: artistNames(limit:offset:sort:), albumSummaries(...), tracksForAlbum(...), searchTracks(...), searchArtistNames(...), searchAlbumSummaries(...)
• Batch query: albumsForArtistsBatch(_:) — fetches album summaries for a full page of artists in one SQL query (IN clause). Use this instead of per-artist albumsForArtist(_:) to avoid N×full-table-scan on the main thread.
• Bulk insert: upsertTracks(_:), upsertMovies(_:), upsertEpisodes(_:) — wrap rows in a transaction; call in 500-row batches during enrichment.
• Alphabet index: artistLetterOffsets(sort:), albumLetterOffsets(sort:) — used by scroll jump-bar.
• Signatures: allSignatures() → [String: FileScanSignature] — loaded once at startup and diffed during incremental scan.

Scan Pipeline

Flow: importMedia(...) in MediaLibrary.swift

1. Discover — LocalFileDiscovery.discoverMedia (recursive + shallow, one-pass resource-key reads).
2. Diff
   • Remove items inside scanned watch folders that are now missing.
   • Skip unchanged files: compare (fileSize, contentModificationDate) signature.
   • Queue changed/new files.
3. Process
   • Fast-track insertion: makeFastTrack / Track.init(lightweightURL:) — avoids eager AVFoundation reads during bulk enqueue.
   • Async metadata enrichment pool: bounded workers (2 on non-local volumes, CPU-based on local).
   • autoreleasepool wraps parseMetadata per file to release AVAsset objects promptly.
   • Incremental 500-track SQLite flushes via flushPendingMetadata() rolling buffer — prevents unbounded memory accumulation on 60k+ libraries.
   • Video classification refresh after audio enrichment completes.
4. Playlists — when includePlaylists: true, discovery.playlistFiles are mapped to LocalPlaylist (incremental: unchanged scan_file_size/scan_mod_date skip rebuild), upsertPlaylists-ed, and mirrored into in-memory playlists/playlistsByPath. Their paths must also join discoveredPaths, and playlist deletion is gated on the same skipCleanup flag as tracks/movies/episodes — otherwise a transiently offline NAS (discovery returns nothing while rows remain) would wipe the Plists list. existingCountInFolders counts tracks/movies/episodes only; that still computes skipCleanup correctly, the playlist delete loop just has to honor it.

Entry Points

scanFolder, rescanWatchFolder, rescanWatchFolders, addTracks(urls:) all route through importMedia(...).

Scan Signatures

FileScanSignature (fileSize: Int64, contentModificationDate: Date) — stored per path in SQLite (scan_file_size, scan_mod_date). Fast-track insertions do not persist a signature; signature is written only after enrichment completes.

Progress Throttling

Emitted when delta >= 0.02 or >= 0.20s elapsed, plus forced boundary emits.

UI Reload Debouncing

Both ModernLibraryBrowserView and PlexBrowserView debounce MediaLibraryDidChange reloads (0.30s work-item debounce) and use mode-aware loadLocalData() to load only required datasets.

LocalFileDiscovery Utility

Utilities/LocalFileDiscovery.swift — shared for all local file/folder discovery, drag-and-drop, and library scanning.

• isSupportedAudioFile(_:), isSupportedVideoFile(_:), isSupportedPlaylistFile(_:), hasSupportedDropContent(...)
• discoverMediaURLsAsync(...) — background discovery, sorted callback on main thread.
• discoverMedia(...) / discoverMediaStreaming(...) — synchronous, used inside scan workers.
• Deduplication by normalized path; one-pass isRegularFile, fileSize, contentModificationDate resource-key reads.
• includePlaylists: Bool = false (on both discoverMedia and discoverMediaStreaming) — when true, .m3u/.pls/.m3u8 files are collected into LocalFileDiscoveryResult.playlistFiles. Only the library scan (importMedia) passes true. Playlists are a third classification: the early guard isAudio || isVideo || isPlaylist includes them, but they do not flow through the audio batch flush (onAudioBatch) and are not in the allURLs computed property (callers treat allURLs as importable audio/video — a .m3u must never be imported as a track).

Video Drop / Add Routing (per-surface, easy to miss)

Video files must be handled explicitly at every drop/add surface — each has its own handler and they are not shared. When adding a new one (or debugging "dragging a video does nothing"), check all of:

• ModernMainWindowView and MainWindowView — the Modern and Classic skins have separate performDragOperations. Both must pass includeVideo: true to hasSupportedDropContent and discoverMediaURLsAsync; the discovered video Track then routes to the video player via the mediaType == .video branch in AudioEngine.loadTrack/playTrack.
• ModernLibraryBrowserView.performDragOperation and PlexBrowserView.performDragOperation — Modern and Classic have separate Library drop handlers. Both route audio to MediaLibrary.addTracks(...) and video to MediaLibrary.addVideoFiles(...); both draggingEntered implementations must allow video (includeVideo: true).
• addVideoFiles() (the +ADD menu) exists in both Library browser implementations — after MediaLibrary.addVideoFiles, call revealLocalVideoCategory() to switch to local → Movies and reload, or the import succeeds but stays hidden on whatever tab is showing. The NSOpenPanel allowed types are built from AudioFileValidator.supportedVideoExtensions so .mkv/.avi/.webm/.ts aren't greyed out.

Track media-type detection uses an extension fallback. Track(url:) first checks asset.tracks(withMediaType: .video), but AVFoundation cannot parse .mkv/.avi/.webm/.flv/.ts (the reason playback uses VLCKit), so that probe returns empty for them. It then falls back to AudioFileValidator.isVideoFile(url:) (extension), so those containers still classify as .video instead of being misrouted to the audio engine. Audio extensions are never in the video set, so real audio can't be misclassified.

NAS Responsiveness

All local AVAudioFile(forReading:) calls are async on deferredIOQueue (background serial queue in AudioEngine).

Deferred Paths (all covered)

Trigger	Function
Direct click (playTrack)	loadLocalTrackForImmediatePlayback(_:at:)
Auto-advance (trackDidFinish)	advanceToLocalTrackAsync → loadLocalTrackForImmediatePlayback
Sweet Fades (startLocalCrossfade)	inline deferredIOQueue.async with crossfadeFileLoadToken
Gapless pre-schedule	scheduleNextTrackForGapless — deferredIOQueue.async

Token-guard Pattern

Each async open carries a load token (deferredLocalTrackLoadToken or crossfadeFileLoadToken). Stale completions are dropped unless token + index + track ID still match at callback time.

Helpers

• prepareForLocalTrackLoad / commitLoadedLocalTrack / handleLocalTrackLoadFailure — shared setup/commit/failure.
• Cue-sheet parsing is async/cancellable (cueLoadTask) in BaseWaveformView.

NAS Playback Temp Copies

For non-local file volumes, direct local playback (loadLocalTrackForImmediatePlayback) and gapless pre-scheduling (scheduleNextTrackForGapless) stage the audio file into the system temp directory before scheduling it. This avoids AVAudioPlayerNode render/pre-fetch reads going back to SMB/NFS during playback or seek. The copy policy is disk-space based, not file-size capped: copy when the temp volume can hold the file while keeping a 1 GiB reserve; otherwise fall back to opening the original NAS path. Temp copies use the nullplayer-playbackcopy- filename prefix (kept distinct from other subsystems' nullplayer-* temp files so the launch sweep only removes playback copies), are removed on track replacement/teardown, and are cleaned on AudioEngine launch to recover files left behind by crashes or force-quits.

⚠️ Tradeoff — large files delay playback start. There is no upper size cap: as long as the temp volume has room (file size + 1 GiB reserve), the entire file is copied on deferredIOQueue before its AVAudioFile opens, so the track does not begin until the copy finishes. On a large file over slow SMB/NFS this can be a multi-second-to-minute delay before first sound (and before a seek target is playable). The payoff is glitch-free playback and seeking afterward. When the temp volume lacks room, playback instead falls back to reading directly from the NAS path — fast start, but subject to render-thread NAS-latency dropouts.

Critical Gotchas

Never call normalizedPath(for:) in a loop over library items

resolvingSymlinksInPath() is a filesystem call — a network round-trip on NFS/SMB. Pre-compute folder paths once outside any loop, then compare against url.path directly (already resolved at scan time via normalizedWatchFolderURL). Violating this caused the Manage Folders window to hang permanently on 60k-track libraries (300k filesystem calls), and a ~20s delay before the remove-folder confirmation appeared (one normalizedPath(for:) per track in removalCountsForWatchFolder/removeWatchFolder).

Reference pattern: watchFolderSummaries(), removalCountsForWatchFolder(), removeWatchFolder(), orphanedEntryCounts(), removeOrphanedEntries() in MediaLibrary.swift — all compare url.path against pre-normalized folder paths, never normalizedPath(for: entry.url).

Never call dataQueue.sync library methods from the main thread

MediaLibrary serializes all mutable state on a private dataQueue, and an import scan holds that queue for many seconds (it does dataQueue.sync per 500-file batch). Any main-thread call into a dataQueue.sync method therefore blocks the UI with a beachball whenever a scan is running — and scans run exactly when the user has just added/rescanned a folder. The expensive offenders: watchFolderSummaries() (four full-array snapshots), removalCountsForWatchFolder(), removeWatchFolder(), and the bare tracksSnapshot/moviesSnapshot/episodesSnapshot copies. Dispatch these to DispatchQueue.global(qos: .userInitiated) (or compute them inside an existing Task.detached) and hop back to main only for UI updates. Reference: WatchFolderManagerWindow.removeSelected() / .reload() and buildLocalFolderItems() in ModernLibraryBrowserView. Still on the main thread (lower-frequency paths, not yet hardened — tracked in #271): loadLocalData() in both browsers and confirmAndRestoreLibrary() in ContextMenuBuilder.

Confirmation dialogs in the Watch Folder manager must be sheets, not free-floating NSAlert.runModal()

WatchFolderManagerWindow sits at .modalPanel level (above always-on-top windows, issue #254). A plain NSAlert.runModal() opens at the normal window level — below the manager window and below floating windows — so it's invisible and can never be confirmed (the removal silently no-ops). Present confirmations with alert.beginSheetModal(for: window): the sheet inherits the parent's level (visible) and is window-modal (blocks the table beneath, so you can't select another row mid-confirm). The completion-handler style also composes cleanly with the off-main count → confirm → off-main delete flow. Reference: confirmRemoval(...) in WatchFolderManagerDialog.swift.

Removing a watch folder must delete from the store, not just memory

The browser reads from the SQLite store (MediaLibraryStore), not MediaLibrary's in-memory arrays. removeWatchFolder(removeEntries:) must call store.deleteTracks/Movies/Episodes(byURLs:) for the removed entries (and store.deleteWatchFolder) — updating only memory leaves removed tracks visible and "removed" folders reappearing on next launch. deleteWatchFolder matches the stored URL via URL(fileURLWithPath:isDirectory:true/false) and the raw path: stored watch-folder URLs are directory URLs with a trailing slash, and on an offline volume URL(fileURLWithPath:) can't stat the path to infer the slash, so a single-form match silently deletes nothing. Orphans not under any current folder (from older buggy removals) are cleaned via removeOrphanedEntries() (Library → Clear… → Remove Orphaned Entries…).

Use albumsForArtistsBatch not per-artist queries in the display layer

albumsForArtist(_:) does one SQL query per artist. In buildLocalArtistItems() on a 200-artist page this means 200 queries, each a full table scan without the expression index (before v2 schema). Always use albumsForArtistsBatch(_:).

Search-result artist navigation must resolve against the final destination list

Both browser implementations (ModernLibraryBrowserView and classic PlexBrowserView) can navigate from Search results to the Artists tab. Do not preserve the clicked search result's row index, and do not rely solely on a server search-result artist ID: Plex search artist IDs can differ from the normal Artists-tab rows. Store the selected artist display name, switch to Artists, rebuild/load the destination list, apply any active column sort, then select the final visible artist row by title (falling back to id only after title match). Local-library search also needs to set localArtistPageOffset from MediaLibraryStore.artistOffset(named:sort:) before loading Artists so paged local artist results land on the page containing the target.

Expression index is load-bearing

idx_tracks_artist_expr uses coalesce(album_artist, artist, 'Unknown Artist') — the same expression used in artistNames GROUP BY and WHERE clauses. If the expression in a query doesn't exactly match the index expression, SQLite won't use the index. Keep query expressions consistent with the index definition.

Fast-track scan signatures

makeFastTrack does not persist a scan signature. The signature (scan_file_size, scan_mod_date) is written only after metadata enrichment completes. This is intentional: if enrichment is interrupted, the file will be re-enriched on next scan.

Plists tab (local playlists) — browser wiring pitfalls

Wired identically in ModernLibraryBrowserView and PlexBrowserView, mirroring the server-playlist pattern (buildSubsonicPlaylistItems). Watch for:

• Two clear-sites per browser must both build the list: loadLocalData() and rebuildCurrentModeItems(). Updating only one makes playlists appear on first load then vanish after any expand/collapse (which re-runs rebuildCurrentModeItems). In modern, rebuildCurrentModeItems had .plists grouped with .radio/.history — split it out, don't string-replace the combined case.
• Key the expand set / track cache by p.url.path (the stable identity), never id.uuidString; read key must equal write key in toggleExpand.
• Lazy parse on expand uses Task.detached { @MainActor … } (NOT plain Task {} — cancellation inheritance gotcha). parsePlaylistTracks(at:) picks Playlist.fromM3U/fromPLS by extension (sync file I/O, hence off-main), resolves each entry via MediaLibrary.shared.findTrack(byURL:) (matched ⇒ toTrack(), unmatched ⇒ Track(lightweightURL:)).
• ItemType gains localPlaylist(LocalPlaylist) / localPlaylistTrack(Track); every switch over ItemType (icons, context menu, double-click, expansion) must handle both. Double-clicking a playlist row plays all its tracks; the disclosure triangle still expands.

Data Tab (Play History Analytics)

Both ModernLibraryBrowserView and PlexBrowserView (classic) embed a Data tab backed by PlayHistoryAgent + StatsContentView.

In PlexBrowserView, the tab is the .history case (displayed as "Data"). It is implemented via an NSHostingView<StatsContentView> created in makeHistoryHostingView() and reused across tab switches. The agent is a private let historyAgent = PlayHistoryAgent() instance on the view. Skin text color is forwarded on tab selection and on skin reload.