---
phase: 01-backing-track-playback-monitoring
plan: 01
subsystem: ui
tags: [react, hooks, jamClient, native-integration, real-time]

# Dependency graph
requires:
  - phase: backing-track-popup-system
    provides: JKSessionBackingTrackPlayer component with play/pause/stop controls
provides:
  - Real-time playback monitoring with 500ms polling
  - M:SS time formatting utility matching legacy web
  - Live-updating current position and duration displays
affects: [02-backing-track-seek-controls, media-player-ui]

# Tech tracking
tech-stack:
  added: []
  patterns: [setInterval polling, formatTime utility, jamClient native method calls]

key-files:
  created: []
  modified: [jam-ui/src/components/client/JKSessionBackingTrackPlayer.js]

key-decisions:
  - "Used setInterval (not setTimeout recursion) for consistent 500ms polling timing"
  - "Polling only runs when isPlaying=true to avoid unnecessary jamClient calls"
  - "Error handling logs to console but continues polling (doesn't crash on transient failures)"
  - "Duration fetched immediately on track load (before playback starts)"

patterns-established:
  - "formatTime utility: milliseconds → M:SS format with no leading zero on minutes"
  - "Polling pattern: useEffect with setInterval, cleanup on pause/stop"
  - "Native client integration: jamClient.SessionCurrrentPlayPosMs(), SessionGetTracksPlayDurationMs(), isSessionTrackPlaying()"

issues-created: []

# Metrics
duration: 15min
completed: 2026-01-13
---

# Phase 1 Plan 1: Backing Track Playback Monitoring Summary

**Real-time backing track playback monitoring with 500ms jamClient polling displaying M:SS formatted time**

## Performance

- **Duration:** 15 min
- **Started:** 2026-01-13T[start-time]
- **Completed:** 2026-01-13T[end-time]
- **Tasks:** 3
- **Files modified:** 1

## Accomplishments
- Added formatTime utility converting milliseconds to M:SS format matching legacy web prettyPrintSeconds behavior
- Implemented 500ms polling with setInterval matching legacy web playbackControls.js pattern
- Wired up currentTime and duration displays to live jamClient data with automatic state syncing
- Duration displays immediately when track loads (before play starts)

## Task Commits

Each task was committed atomically:

1. **Task 1: Add formatTime utility function** - `df94ec7d0` (feat)
2. **Task 2: Add playback monitoring with 500ms polling** - `e33983e15` (feat)
3. **Task 3: Initialize duration on track load** - `84b3b2ccb` (feat)

## Files Created/Modified
- `jam-ui/src/components/client/JKSessionBackingTrackPlayer.js` - Added formatTime utility, 500ms polling useEffect, and duration initialization on track load

## Decisions Made
- **setInterval over setTimeout recursion:** Chose setInterval for consistent 500ms timing rather than recursive setTimeout pattern. This ensures polling happens exactly every 500ms regardless of execution time.
- **Polling activation:** Only poll when isPlaying=true to avoid unnecessary jamClient calls when paused/stopped. This reduces CPU usage and native client overhead.
- **Error handling strategy:** Log errors to console but continue polling. This prevents transient jamClient failures from crashing the UI while still providing visibility.
- **Immediate duration fetch:** Fetch duration on track load (before play) so users see total length immediately, matching legacy web UI behavior.

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered

None - straightforward implementation matching legacy web pattern.

## Next Phase Readiness

Phase 2 (Backing Track Seek Controls) can now proceed. The monitoring useEffect establishes the foundation for:
- Seek slider reflecting current position (value driven by currentTime state)
- Seeking will need slight modification to polling (pause briefly during drag, resume after seek)
- Duration already available for slider max value

All verification criteria met:
- Duration displays immediately when track opens
- Current time updates every ~500ms during playback
- Time format matches M:SS specification (no leading zero on minutes)
- Polling stops cleanly on pause/stop
- No console errors during playback
- Both modal and popup versions work identically

---
*Phase: 01-backing-track-playback-monitoring*
*Completed: 2026-01-13*
