led2/.planning/phases/06-ai-sync/06-02-SUMMARY.md

phase, plan, subsystem, tags, dependency_graph, tech_stack, key_files, decisions, metrics, requirements_satisfied

phase	plan	subsystem	tags	dependency_graph	tech_stack	key_files	decisions	metrics	requirements_satisfied
06-ai-sync	02	audio-analysis	librosa segmentation feature-extraction canvas-overlay timeline	requires provides affects 06-01 audio-features structural-segments segment-overlay-ui lightsync/audio lightsync/api/audio.py lightsync/frontend/timeline	added patterns asyncio.to_thread for CPU-bound librosa analysis canvas overlay layer agglomerative clustering	created modified lightsync/audio/features.py lightsync/audio/segments.py lightsync/frontend/timeline/segments.js lightsync/api/audio.py lightsync/main.py lightsync/frontend/timeline/timeline.js lightsync/frontend/app.js	Segment band drawing inserted between step 2 (track row banding) and step 3 (waveform) in render() for correct Z-order agglomerative returns k boundaries yielding k+1 sections — all_times = [0.0] + bound_times + [duration] pattern Auto segment count heuristic: max(4, min(12, int(duration / 30))) — 4-12 sections for typical songs Segment click handling added on empty-canvas clicks only — block interactions take priority BAND_COLORS alternates 3 colors (cyan, purple, darker-cyan) for visual variety	duration completed tasks_completed files_changed ~8 min 2026-04-07 2 7	SYNC-03

Phase 06 Plan 02: Audio Feature Extraction and Segment Overlay Summary

One-liner: Librosa-based audio feature extraction (onsets, chroma, RMS) and structural segmentation with interactive translucent section bands on the timeline canvas.

What Was Built

Added structural audio analysis foundation for the AI sync engine and visible segment overlay UI:

1. Feature extraction backend (Task 1, partial): New lightsync/audio/features.py module:

   • extract_features(path) extracts onset_times, rms_1s, chroma_1s, duration, sr
   • Uses librosa onset detection, chroma_cqt, and RMS energy; reduces to 1s resolution
   • extract_features_async wraps in asyncio.to_thread

2. Segmentation backend (Task 1, partial): New lightsync/audio/segments.py module:

   • detect_segments(path, n_segments=None) uses chroma + recurrence matrix + agglomerative clustering
   • Auto segment count heuristic: max(4, min(12, int(duration / 30))) for 4-12 sections
   • Returns [{"start": float, "end": float, "label": "SEC N"}, ...]
   • detect_segments_async wraps in asyncio.to_thread

3. API endpoints (Task 1, partial):

   • GET /api/audio/segments?path=... — returns cached structural segments
   • GET /api/audio/features?path=... — returns onsets, chroma, RMS
   • Both endpoints added to lightsync/api/audio.py
   • app.state.segments = {} cache initialized in main.py lifespan

4. Segment overlay UI (Task 2): New lightsync/frontend/timeline/segments.js:

   • SegmentOverlay class manages segment data, drawing, and click interaction
   • draw() renders translucent colored bands using BAND_COLORS (cyan/purple alternation)
   • handleClick(time) selects segment containing that time, deselects on empty click
   • getSelected() returns currently selected segment or null
   • Labels render as SEC 1, SEC 2, etc. in 9px monospace at top-left of each band
   • Selected band highlighted with 1px rgba(0,255,255,1.0) border

5. Timeline integration (Task 2):

   • import { SegmentOverlay } added to timeline.js
   • this.segmentOverlay = new SegmentOverlay() in constructor
   • segmentOverlay.draw() inserted between step 2 (row banding) and step 3 (waveform) in render()
   • async loadSegments(audioPath) method added to TimelineCanvas
   • Segment click handling in mousedown: empty-canvas clicks update segment selection
   • timeline.loadSegments(path) called in app.js loadedmetadata handler

Commits

Task	Commit	Description
1	d339ba5	feat(06-02): add feature extraction and segmentation backend modules + API
2	48e15ee	feat(06-02): add segment overlay canvas rendering and click interaction

Deviations from Plan

None - plan executed exactly as written.

Known Stubs

None - all functionality is fully wired.

Self-Check: PASSED

• lightsync/audio/features.py exists: contains def extract_features, async def extract_features_async, librosa.onset.onset_detect, librosa.feature.chroma_cqt, librosa.feature.rms, returns keys onset_times, rms_1s, chroma_1s, duration, sr
• lightsync/audio/segments.py exists: contains def detect_segments, async def detect_segments_async, librosa.segment.agglomerative, librosa.segment.recurrence_matrix, SEC {i + 1}, max(4, min(12,
• lightsync/api/audio.py contains async def get_segments, async def get_features, from lightsync.audio.segments import detect_segments_async, from lightsync.audio.features import extract_features_async
• lightsync/main.py contains app.state.segments = {}
• lightsync/frontend/timeline/segments.js exists: contains class SegmentOverlay, export { SegmentOverlay }, BAND_COLORS, rgba(0,255,255,0.15), rgba(180,0,255,0.15), handleClick, getSelected, seg.label, 9px monospace
• lightsync/frontend/timeline/timeline.js contains import { SegmentOverlay }, this.segmentOverlay = new SegmentOverlay(), segmentOverlay.draw(, async loadSegments(audioPath)
• lightsync/frontend/app.js contains loadSegments(path) in loadedmetadata handler
• All task commits exist: d339ba5, 48e15ee