axiom-now-playing（公理正在播放）

Now Playing Integration Guide

Purpose: Prevent the 4 most common Now Playing issues on iOS 18+: info not appearing, commands not working, artwork problems, and state sync issues

Swift Version: Swift 6.0+ iOS Version: iOS 18+ Xcode: Xcode 16+

Core Philosophy

"Now Playing eligibility requires THREE things working together: AVAudioSession activation, remote command handlers, and metadata publishing. Missing ANY of these silently breaks the entire system. 90% of Now Playing issues stem from incorrect activation order or missing command handlers, not API bugs."

Key Insight from WWDC 2022/110338: Apps must meet two system heuristics:

1. Register handlers for at least one remote command
2. Configure AVAudioSession with a non-mixable category

When to Use This Skill

✅ Use this skill when:

• Now Playing info doesn't appear on Lock Screen or Control Center
• Play/pause/skip buttons are grayed out or don't respond
• Album artwork is missing, wrong, or flickers between images
• Control Center shows "Playing" when app is paused, or vice versa
• Apple Music or other apps "steal" Now Playing status
• Implementing Now Playing for the first time
• Debugging Now Playing issues in existing implementation
• Integrating CarPlay Now Playing (covered in Pattern 6)
• Working with MusicKit/Apple Music content (covered in Pattern 7)

iOS 26 Note

iOS 26 introduces Liquid Glass visual design for Lock Screen and Control Center Now Playing widgets. This is automatic system behavior — no code changes required. The patterns in this skill remain valid for iOS 26.

❌ Do NOT use this skill for:

• Background audio configuration details (see AVFoundation skill)

Related Skills

• swift-concurrency - For @MainActor patterns, weak self in closures, async artwork loading
• memory-debugging - For retain cycles in command handlers
• avfoundation-ref - For AVAudioSession configuration details

Red Flags / Anti-Patterns

If you see ANY of these, suspect Now Playing misconfiguration:

• Info appears briefly then disappears (AVAudioSession deactivated)
• Commands work in simulator but not on device (simulator has different audio stack)
• Artwork shows placeholder then updates (race condition, not necessarily wrong)
• Artwork never appears (format/size issue or MPMediaItemArtwork block returning nil)
• Play/pause state incorrect after backgrounding (not updating on playback rate changes)
• Another app "steals" Now Playing (didn't meet eligibility requirements)
• playbackState property doesn't update (iOS doesn't have playbackState, macOS only!)

FORBIDDEN Assumptions:

• "Just set nowPlayingInfo and it works" - Must have AVAudioSession + command handlers
• "playbackState controls Control Center" - iOS ignores playbackState, uses playbackRate
• "Artwork just needs an image" - Needs proper MPMediaItemArtwork with size handler
• "Commands enable themselves" - Must add target AND set isEnabled = true
• "Update elapsed time every second" - System infers from rate, causes jitter

Mandatory First Steps (Pre-Diagnosis)

Run this code to understand current state before debugging:

// 1. Verify AVAudioSession configuration
let session = AVAudioSession.sharedInstance()
print("Category: \(session.category.rawValue)")
print("Mode: \(session.mode.rawValue)")
print("Options: \(session.categoryOptions)")
print("Is active: \(try? session.setActive(true))")
// Must be: .playback category, NOT .mixWithOthers option

// 2. Verify background mode
// Info.plist must have: UIBackgroundModes = ["audio"]

// 3. Check command handlers are registered
let commandCenter = MPRemoteCommandCenter.shared()
print("Play enabled: \(commandCenter.playCommand.isEnabled)")
print("Pause enabled: \(commandCenter.pauseCommand.isEnabled)")
// Must have at least one command with target AND isEnabled = true

// 4. Check nowPlayingInfo dictionary
if let info = MPNowPlayingInfoCenter.default().nowPlayingInfo {
    print("Title: \(info[MPMediaItemPropertyTitle] ?? "nil")")
    print("Artwork: \(info[MPMediaItemPropertyArtwork] != nil)")
    print("Duration: \(info[MPMediaItemPropertyPlaybackDuration] ?? "nil")")
    print("Elapsed: \(info[MPNowPlayingInfoPropertyElapsedPlaybackTime] ?? "nil")")
    print("Rate: \(info[MPNowPlayingInfoPropertyPlaybackRate] ?? "nil")")
} else {
    print("No nowPlayingInfo set!")
}

What this tells you:

Decision Tree

Now Playing not working?
├─ Info never appears at all?
│  ├─ AVAudioSession category .ambient or .mixWithOthers?
│  │  └─ Pattern 1a (Wrong Category)
│  ├─ No remote command handlers registered?
│  │  └─ Pattern 2a (Missing Handlers)
│  ├─ Background mode "audio" not in Info.plist?
│  │  └─ Pattern 1b (Background Mode)
│  └─ AVAudioSession.setActive(true) never called?
│     └─ Pattern 1c (Not Activated)
│
├─ Info appears briefly, then disappears?
│  ├─ On lock screen specifically?
│  │  ├─ AVAudioSession deactivated too early?
│  │  │  └─ Pattern 1d (Early Deactivation)
│  │  └─ App suspended (no background mode)?
│  │     └─ Pattern 1b (Background Mode)
│  └─ When switching apps?
│     └─ Another app claiming Now Playing → Pattern 5
│
├─ Commands not responding?
│  ├─ Buttons grayed out (disabled)?
│  │  └─ command.isEnabled = false → Pattern 2b
│  ├─ Buttons visible but no response?
│  │  ├─ Handler not returning .success?
│  │  │  └─ Pattern 2c (Handler Return)
│  │  └─ Using wrong command center (session vs shared)?
│  │     └─ Pattern 2d (Command Center)
│  └─ Skip forward/backward not showing?
│     └─ preferredIntervals not set → Pattern 2e
│
├─ Artwork problems?
│  ├─ Never appears?
│  │  ├─ MPMediaItemArtwork block returning nil?
│  │  │  └─ Pattern 3a (Artwork Block)
│  │  └─ Image format/size invalid?
│  │     └─ Pattern 3b (Image Format)
│  ├─ Wrong artwork showing?
│  │  └─ Race condition between sources → Pattern 3c
│  └─ Artwork flickering?
│     └─ Multiple updates in rapid succession → Pattern 3d
│
├─ State sync issues?
│  ├─ Shows "Playing" when paused?
│  │  └─ playbackRate not updated → Pattern 4a
│  ├─ Progress bar stuck or jumping?
│  │  └─ elapsedTime not updated at right moments → Pattern 4b
│  └─ Duration wrong?
│     └─ Not setting playbackDuration → Pattern 4c
│
├─ CarPlay specific issues?
│  ├─ App doesn't appear in CarPlay at all?
│  │  └─ Missing entitlement → Pattern 6 (Add com.apple.developer.carplay-audio)
│  ├─ Now Playing blank in CarPlay but works on iOS?
│  │  └─ Same root cause as iOS → Check Patterns 1-4
│  ├─ Custom buttons don't appear in CarPlay?
│  │  └─ Wrong configuration timing → Pattern 6 (Configure at templateApplicationScene)
│  └─ Works on device but not CarPlay simulator?
│     └─ Debugger interference → Pattern 6 (Run without debugger)
│
└─ Using MusicKit (ApplicationMusicPlayer)?
   ├─ Now Playing shows wrong info?
   │  └─ Overwriting automatic data → Pattern 7 (Don't set nowPlayingInfo manually)
   └─ Mixing MusicKit + own content?
      └─ Hybrid approach needed → Pattern 7 (Switch between players)

Pattern 1: AVAudioSession Configuration (Info Not Appearing)

Time cost: 10-15 minutes

Symptom

• Now Playing info never appears on Lock Screen
• Info appears briefly then disappears on lock
• Works in foreground, disappears in background

BAD Code

// ❌ WRONG — Category allows mixing, won't become Now Playing app
class PlayerService {
    func setupAudioSession() throws {
        try AVAudioSession.sharedInstance().setCategory(
            .playback,
            options: .mixWithOthers  // ❌ Mixable = not eligible for Now Playing
        )
        // Never called setActive()  // ❌ Session not activated
    }

    func play() {
        player.play()
        updateNowPlaying()  // ❌ Won't appear - session not active
    }
}

GOOD Code

// ✅ CORRECT — Non-mixable category, activated before playback
class PlayerService {
    func setupAudioSession() throws {
        try AVAudioSession.sharedInstance().setCategory(
            .playback,
            mode: .default,
            options: []  // ✅ No .mixWithOthers = eligible for Now Playing
        )
    }

    func play() async throws {
        // ✅ Activate BEFORE starting playback
        try AVAudioSession.sharedInstance().setActive(true)

        player.play()
        updateNowPlaying()  // ✅ Now appears correctly
    }

    func stop() async throws {
        player.pause()

        // ✅ Deactivate AFTER stopping, with notify option
        try AVAudioSession.sharedInstance().setActive(
            false,
            options: .notifyOthersOnDeactivation
        )
    }
}

Info.plist Requirement

<key>UIBackgroundModes</key>
<array>
    <string>audio</string>
</array>

Verification

• Lock screen shows Now Playing controls
• Info persists when app backgrounded
• Survives app switch (unless another app plays)

Pattern 2: Remote Command Registration (Commands Not Working)

Time cost: 15-20 minutes

Symptom

• Play/pause buttons grayed out
• Buttons visible but tapping does nothing
• Skip buttons don't appear
• Commands work once then stop

BAD Code

// ❌ WRONG — Missing targets and isEnabled
class PlayerService {
    func setupCommands() {
        let commandCenter = MPRemoteCommandCenter.shared()

        // ❌ Added target but forgot isEnabled
        commandCenter.playCommand.addTarget { _ in
            self.player.play()
            return .success
        }
        // playCommand.isEnabled defaults to false!

        // ❌ Never added pause handler

        // ❌ skipForward without preferredIntervals
        commandCenter.skipForwardCommand.addTarget { _ in
            return .success
        }
    }
}

GOOD Code

// ✅ CORRECT — Targets registered, enabled, with proper configuration
@MainActor
class PlayerService {
    private var commandTargets: [Any] = []  // Keep strong references

    func setupCommands() {
        let commandCenter = MPRemoteCommandCenter.shared()

        // ✅ Play command - add target AND enable
        let playTarget = commandCenter.playCommand.addTarget { [weak self] _ in
            self?.player.play()
            self?.updateNowPlayingPlaybackState(isPlaying: true)
            return .success
        }
        commandCenter.playCommand.isEnabled = true
        commandTargets.append(playTarget)

        // ✅ Pause command
        let pauseTarget = commandCenter.pauseCommand.addTarget { [weak self] _ in
            self?.player.pause()
            self?.updateNowPlayingPlaybackState(isPlaying: false)
            return .success
        }
        commandCenter.pauseCommand.isEnabled = true
        commandTargets.append(pauseTarget)

        // ✅ Skip forward - set preferredIntervals BEFORE adding target
        commandCenter.skipForwardCommand.preferredIntervals = [15.0]
        let skipForwardTarget = commandCenter.skipForwardCommand.addTarget { [weak self] event in
            guard let skipEvent = event as? MPSkipIntervalCommandEvent else {
                return .commandFailed
            }
            self?.skip(by: skipEvent.interval)
            return .success
        }
        commandCenter.skipForwardCommand.isEnabled = true
        commandTargets.append(skipForwardTarget)

        // ✅ Skip backward
        commandCenter.skipBackwardCommand.preferredIntervals = [15.0]
        let skipBackwardTarget = commandCenter.skipBackwardCommand.addTarget { [weak self] event in
            guard let skipEvent = event as? MPSkipIntervalCommandEvent else {
                return .commandFailed
            }
            self?.skip(by: -skipEvent.interval)
            return .success
        }
        commandCenter.skipBackwardCommand.isEnabled = true
        commandTargets.append(skipBackwardTarget)
    }

    func teardownCommands() {
        let commandCenter = MPRemoteCommandCenter.shared()
        commandCenter.playCommand.removeTarget(nil)
        commandCenter.pauseCommand.removeTarget(nil)
        commandCenter.skipForwardCommand.removeTarget(nil)
        commandCenter.skipBackwardCommand.removeTarget(nil)
        commandTargets.removeAll()
    }

    deinit {
        teardownCommands()
    }
}

Verification

• Buttons not grayed out in Control Center
• Tapping play/pause actually plays/pauses
• Skip buttons show with correct interval (15s)

Pattern 3: Artwork Configuration (Artwork Problems)

Time cost: 15-25 minutes

Symptom

• Artwork never appears (generic placeholder)
• Wrong artwork for current track
• Artwork flickers between images
• Artwork appears then disappears

BAD Code

// ❌ WRONG — MPMediaItemArtwork block can return nil, no size handling
func updateNowPlaying() {
    var nowPlayingInfo = [String: Any]()
    nowPlayingInfo[MPMediaItemPropertyTitle] = track.title

    // ❌ Storing UIImage directly (doesn't work)
    nowPlayingInfo[MPMediaItemPropertyArtwork] = image

    // ❌ Or: Block that ignores requested size
    let artwork = MPMediaItemArtwork(boundsSize: image.size) { _ in
        return self.cachedImage  // ❌ May be nil, ignores requested size
    }

    MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo
}

// ❌ WRONG — Multiple rapid updates cause flickering
func loadArtwork(from url: URL) {
    // Request 1
    loadImage(url) { image in
        self.updateNowPlayingArtwork(image)  // Update 1
    }
    // Request 2 (cached) returns faster
    loadCachedImage(url) { image in
        self.updateNowPlayingArtwork(image)  // Update 2 - flicker!
    }
}

GOOD Code

// ✅ CORRECT — Proper MPMediaItemArtwork with value capture (Swift 6 compliant)
@MainActor
class NowPlayingService {
    private var currentArtworkURL: URL?

    func updateNowPlayingArtwork(_ image: UIImage, for trackURL: URL) {
        // ✅ Prevent race conditions - only update if still current track
        guard trackURL == currentArtworkURL else { return }

        // ✅ Create MPMediaItemArtwork with VALUE CAPTURE (not stored property)
        // This is Swift 6 strict concurrency compliant — UIImage is immutable
        // and safe to capture across isolation domains
        let artwork = MPMediaItemArtwork(boundsSize: image.size) { [image] requestedSize in
            // ✅ System calls this block from any thread
            // Captured value avoids "Main actor-isolated property" error
            return image
        }

        // ✅ Update only artwork key, preserve other values
        var nowPlayingInfo = MPNowPlayingInfoCenter.default().nowPlayingInfo ?? [:]
        nowPlayingInfo[MPMediaItemPropertyArtwork] = artwork
        MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo
    }

    // ✅ Single entry point with priority: embedded > cached > remote
    func loadArtwork(for track: Track) async {
        currentArtworkURL = track.artworkURL

        // Priority 1: Embedded in file (immediate, no flicker)
        if let embedded = await extractEmbeddedArtwork(track.fileURL) {
            updateNowPlayingArtwork(embedded, for: track.artworkURL)
            return
        }

        // Priority 2: Already cached (fast)
        if let cached = await loadFromCache(track.artworkURL) {
            updateNowPlayingArtwork(cached, for: track.artworkURL)
            return
        }

        // Priority 3: Remote (slow, but don't flicker)
        // ✅ Set placeholder first, then update once with real image
        if let remote = await downloadImage(track.artworkURL) {
            updateNowPlayingArtwork(remote, for: track.artworkURL)
        }
    }
}

Why value capture, not nonisolated(unsafe): The closure passed to MPMediaItemArtwork may be called by the system from any thread. Under Swift 6 strict concurrency, accessing @MainActor-isolated stored properties from this closure would cause a compile error. Capturing the image value directly is cleaner than using nonisolated(unsafe) because UIImage is immutable and thread-safe for reads.

Artwork Size Guidelines

• Lock Screen: 300x300 points (600x600 @2x, 900x900 @3x)
• Control Center: Various sizes
• Best practice: Provide image at least 600x600 pixels

Verification

• Artwork appears on Lock Screen
• Correct artwork for current track
• No flickering when track changes
• Artwork persists after backgrounding

Pattern 4: Playback State Synchronization (State Sync Issues)

Time cost: 10-20 minutes

Symptom

• Control Center shows "Playing" when actually paused
• Progress bar doesn't move or jumps unexpectedly
• Duration shows wrong value
• Scrubbing doesn't work correctly

BAD Code

// ❌ WRONG — Using playbackState (macOS only, ignored on iOS)
func updatePlaybackState(isPlaying: Bool) {
    MPNowPlayingInfoCenter.default().playbackState = isPlaying ? .playing : .paused
    // ❌ iOS ignores this property! Only macOS uses it.
}

// ❌ WRONG — Updating elapsed time on a timer (causes drift)
Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in
    var info = MPNowPlayingInfoCenter.default().nowPlayingInfo ?? [:]
    info[MPNowPlayingInfoPropertyElapsedPlaybackTime] = self.player.currentTime().seconds
    MPNowPlayingInfoCenter.default().nowPlayingInfo = info
    // ❌ Every second creates jitter, system already infers from timestamp
}

// ❌ WRONG — Partial dictionary updates cause race conditions
func updateTitle() {
    var info = [String: Any]()
    info[MPMediaItemPropertyTitle] = track.title
    MPNowPlayingInfoCenter.default().nowPlayingInfo = info
    // ❌ Cleared all other values (artwork, duration, etc.)!
}

GOOD Code

// ✅ CORRECT — Use playbackRate for iOS, update at key moments only
@MainActor
class NowPlayingService {

    // ✅ Update when playback STARTS
    func playbackStarted(track: Track, player: AVPlayer) {
        var nowPlayingInfo = MPNowPlayingInfoCenter.default().nowPlayingInfo ?? [:]

        // ✅ Core metadata
        nowPlayingInfo[MPMediaItemPropertyTitle] = track.title
        nowPlayingInfo[MPMediaItemPropertyArtist] = track.artist
        nowPlayingInfo[MPMediaItemPropertyAlbumTitle] = track.album
        nowPlayingInfo[MPMediaItemPropertyPlaybackDuration] = player.currentItem?.duration.seconds ?? 0

        // ✅ Playback state via RATE (not playbackState property)
        nowPlayingInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = player.currentTime().seconds
        nowPlayingInfo[MPNowPlayingInfoPropertyPlaybackRate] = 1.0  // Playing

        MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo
    }

    // ✅ Update when playback PAUSES
    func playbackPaused(player: AVPlayer) {
        var nowPlayingInfo = MPNowPlayingInfoCenter.default().nowPlayingInfo ?? [:]

        // ✅ Update elapsed time AND rate together
        nowPlayingInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = player.currentTime().seconds
        nowPlayingInfo[MPNowPlayingInfoPropertyPlaybackRate] = 0.0  // Paused

        MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo
    }

    // ✅ Update when user SEEKS
    func userSeeked(to time: CMTime, player: AVPlayer) {
        var nowPlayingInfo = MPNowPlayingInfoCenter.default().nowPlayingInfo ?? [:]

        nowPlayingInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = time.seconds
        // ✅ Keep current rate (don't change playing/paused state)

        MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo
    }

    // ✅ Update when track CHANGES
    func trackChanged(to newTrack: Track, player: AVPlayer) {
        // ✅ Full refresh of all metadata
        var nowPlayingInfo = [String: Any]()

        nowPlayingInfo[MPMediaItemPropertyTitle] = newTrack.title
        nowPlayingInfo[MPMediaItemPropertyArtist] = newTrack.artist
        nowPlayingInfo[MPMediaItemPropertyAlbumTitle] = newTrack.album
        nowPlayingInfo[MPMediaItemPropertyPlaybackDuration] = player.currentItem?.duration.seconds ?? 0
        nowPlayingInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = 0.0
        nowPlayingInfo[MPNowPlayingInfoPropertyPlaybackRate] = player.rate

        MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo

        // Then load artwork asynchronously
        Task {
            await loadArtwork(for: newTrack)
        }
    }
}

When to Update Now Playing Info

DO NOT Update

• On a timer (system infers from elapsed + rate + timestamp)
• Elapsed time continuously (causes jitter)
• Partial dictionaries (loses other values)

Pattern 5: MPNowPlayingSession (iOS 16+ Recommended Approach)

Time cost: 20-30 minutes

When to Use MPNowPlayingSession

• iOS 16+ (available since iOS 16, previously tvOS only)
• Using AVPlayer for playback
• Want automatic publishing of playback state
• Multiple players (Picture-in-Picture scenarios)

BAD Code (Manual Approach - More Error-Prone)

// ❌ Manual updates are error-prone, easy to miss state changes
class OldStylePlayer {
    func play() {
        player.play()
        // Must remember to:
        updateNowPlayingElapsed()
        updateNowPlayingRate()
        // Easy to forget one...
    }
}

GOOD Code (MPNowPlayingSession)

// ✅ CORRECT — MPNowPlayingSession handles automatic publishing
@MainActor
class ModernPlayerService {
    private var player: AVPlayer
    private var session: MPNowPlayingSession?

    init() {
        player = AVPlayer()
        setupSession()
    }

    func setupSession() {
        // ✅ Create session with player
        session = MPNowPlayingSession(players: [player])

        // ✅ Enable automatic publishing of:
        // - Duration
        // - Elapsed time
        // - Playback state (rate)
        // - Playback progress
        session?.automaticallyPublishNowPlayingInfo = true

        // ✅ Register commands on SESSION's command center (not shared)
        session?.remoteCommandCenter.playCommand.addTarget { [weak self] _ in
            self?.player.play()
            return .success
        }
        session?.remoteCommandCenter.playCommand.isEnabled = true

        session?.remoteCommandCenter.pauseCommand.addTarget { [weak self] _ in
            self?.player.pause()
            return .success
        }
        session?.remoteCommandCenter.pauseCommand.isEnabled = true

        // ✅ Try to become active Now Playing session
        session?.becomeActiveIfPossible { success in
            print("Became active Now Playing: \(success)")
        }
    }

    func play(track: Track) async {
        let item = AVPlayerItem(url: track.url)

        // ✅ Set static metadata on player item (title, artwork)
        item.nowPlayingInfo = [
            MPMediaItemPropertyTitle: track.title,
            MPMediaItemPropertyArtist: track.artist,
            MPMediaItemPropertyArtwork: await createArtwork(for: track)
        ]

        player.replaceCurrentItem(with: item)
        player.play()
        // ✅ No need to manually update elapsed time, rate, duration
        // MPNowPlayingSession publishes automatically!
    }
}

Multiple Sessions (Picture-in-Picture)

class MultiPlayerService {
    var mainSession: MPNowPlayingSession
    var pipSession: MPNowPlayingSession

    func pipDidExpand() {
        // ✅ Promote PiP session when it expands to full screen
        pipSession.becomeActiveIfPossible { success in
            // PiP now controls Lock Screen, Control Center
        }
    }

    func pipDidMinimize() {
        // ✅ Demote back to main session
        mainSession.becomeActiveIfPossible { success in
            // Main player now controls Lock Screen, Control Center
        }
    }
}

Critical Gotcha

When using MPNowPlayingSession: Use session.remoteCommandCenter, NOT MPRemoteCommandCenter.shared()

// ❌ WRONG
let commandCenter = MPRemoteCommandCenter.shared()
commandCenter.playCommand.addTarget { _ in }

// ✅ CORRECT
session.remoteCommandCenter.playCommand.addTarget { _ in }

Pattern 6: CarPlay Integration

For CarPlay-specific integration patterns, invoke /skill axiom-now-playing-carplay.

Key insight: CarPlay uses the SAME MPNowPlayingInfoCenter and MPRemoteCommandCenter as iOS. If your Now Playing works on iOS, it works in CarPlay with zero additional code.

Pattern 7: MusicKit Integration (Apple Music)

For MusicKit-specific integration patterns and hybrid app examples, invoke /skill axiom-now-playing-musickit.

Key insight: MusicKit's ApplicationMusicPlayer automatically publishes to MPNowPlayingInfoCenter. You don't need to manually update Now Playing info when playing Apple Music content.

Pressure Scenarios

Scenario 1: Apple Music Keeps Taking Over (24-Hour Launch Deadline)

Situation

• App launching tomorrow
• QA reports: "Now Playing works, but when user opens Apple Music then returns to our app, our controls disappear"
• Product manager: "This is a blocker, users will think our app is broken"
• You're 2 hours from code freeze

Rationalization Traps (DO NOT)

1. *"Just tell users not to use Apple Music"* - Unacceptable UX, will get 1-star reviews
2. *"Force our app to always be Now Playing"* - Impossible, system controls eligibility
3. *"File a bug with Apple"* - Won't help before launch

Root Cause

Your app loses eligibility because:

• Using .mixWithOthers option (allows other apps to play simultaneously)
• Not calling becomeActiveIfPossible() when returning to foreground
• AVAudioSession deactivated when backgrounded

Systematic Fix (30 minutes)

// 1. Remove mixWithOthers
try AVAudioSession.sharedInstance().setCategory(.playback, options: [])

// 2. Reactivate when returning to foreground
NotificationCenter.default.addObserver(
    forName: UIApplication.willEnterForegroundNotification,
    object: nil,
    queue: .main
) { [weak self] _ in
    guard self?.isPlaying == true else { return }

    do {
        try AVAudioSession.sharedInstance().setActive(true)
        self?.session?.becomeActiveIfPossible { _ in }
    } catch {
        print("Failed to reactivate audio session: \(error)")
    }
}

// 3. Handle interruptions (phone call, Siri)
NotificationCenter.default.addObserver(
    forName: AVAudioSession.interruptionNotification,
    object: nil,
    queue: .main
) { [weak self] notification in
    guard let info = notification.userInfo,
          let typeValue = info[AVAudioSessionInterruptionTypeKey] as? UInt,
          let type = AVAudioSession.InterruptionType(rawValue: typeValue) else {
        return
    }

    if type == .ended {
        // ✅ Reactivate after interruption
        try? AVAudioSession.sharedInstance().setActive(true)
        self?.session?.becomeActiveIfPossible { _ in }
    }
}

Communication Template

To PM: Found root cause - our audio session config allowed Apple Music to take over.
Fix implemented: 3 changes to audio session handling.
Testing: Verified fix with Apple Music, Spotify, phone calls.
ETA: 20 more minutes for full regression test.

To QA: Please test this flow:
1. Play audio in our app
2. Open Apple Music, play a song
3. Return to our app, tap play
4. Lock screen should show OUR controls

Time Saved

• 2-3 hours of debugging speculation
• Launch delay avoided
• QA confidence restored

Scenario 2: Artwork Flickers Every Track Change

Situation

• User feedback: "Album art keeps flashing when songs change"
• Analytics show 3-4 artwork updates per track change
• Designer: "This looks unprofessional"

Root Cause

Multiple artwork sources racing:

1. Cache check (async)
2. Remote URL fetch (async)
3. Embedded artwork extraction (async)

All three complete at different times, each updating Now Playing

Fix (20 minutes)

// ✅ Single-source-of-truth with cancellation
private var artworkTask: Task<Void, Never>?

func loadArtwork(for track: Track) {
    // Cancel previous artwork load
    artworkTask?.cancel()

    artworkTask = Task { @MainActor in
        // Clear previous artwork immediately (optional)
        // updateNowPlayingArtwork(nil)

        // Wait for best available artwork
        let artwork = await loadBestArtwork(for: track)

        // Check if still current track
        guard !Task.isCancelled else { return }

        // Single update
        updateNowPlayingArtwork(artwork, for: track.artworkURL)
    }
}

private func loadBestArtwork(for track: Track) async -> UIImage? {
    // Priority order: embedded > cached > remote
    if let embedded = await extractEmbeddedArtwork(track) {
        return embedded
    }
    if let cached = await loadFromCache(track.artworkURL) {
        return cached
    }
    return await downloadImage(track.artworkURL)
}

Communication Template

To Designer: Fixed artwork flicker - reduced from 3-4 updates to 1 per track.
Root cause: Multiple async sources racing to update artwork.
Solution: Task cancellation + priority order (embedded > cached > remote).
Testing: Verified with 10 track changes, zero flicker.

Time Saved

• 1-2 hours investigating image caching
• Designer approval unblocked
• Professional UX restored

Common Gotchas

Expert Checklist

Before Implementing Now Playing

• Added audio to UIBackgroundModes in Info.plist
• AVAudioSession category is .playback without .mixWithOthers
• Decided: Manual (MPNowPlayingInfoCenter) or Automatic (MPNowPlayingSession)?

AVAudioSession Setup

• setCategory(.playback) called at app launch
• setActive(true) called before playback starts
• setActive(false, options:.notifyOthersOnDeactivation) on stop
• Interruption notification handled (reactivate after phone call)
• Foreground notification handled (reactivate after background)

Remote Commands

• At least one command has target registered
• All registered commands have isEnabled = true
• Skip commands have preferredIntervals set
• Handlers return .success on success
• Using correct command center (session's vs shared)
• Command targets stored to prevent deallocation
• Commands removed in deinit

Now Playing Info

• Title set (MPMediaItemPropertyTitle)
• Duration set (MPMediaItemPropertyPlaybackDuration)
• Elapsed time set at play/pause/seek (MPNowPlayingInfoPropertyElapsedPlaybackTime)
• Playback rate set (MPNowPlayingInfoPropertyPlaybackRate: 1.0 = playing, 0.0 = paused)
• Artwork created with MPMediaItemArtwork(boundsSize:requestHandler:)
• NOT using playbackState property (macOS only)
• NOT updating elapsed time on a timer

Artwork

• Image at least 600x600 pixels
• MPMediaItemArtwork block never returns nil (return placeholder if needed)
• Single source of truth prevents flickering
• Previous artwork load cancelled on track change

Testing

• Lock screen shows correct info
• Control Center shows correct info
• Play/pause buttons respond
• Skip buttons show and respond
• Progress bar moves correctly
• Survives app background/foreground
• Survives phone call interruption
• Survives other app playing audio
• Tested with Apple Music conflict
• Tested with Spotify conflict

CarPlay (if applicable)

• Added com.apple.developer.carplay-audio entitlement
• CPNowPlayingTemplate configured at templateApplicationScene(_:didConnect:)
• Custom buttons (if any) configured with CPNowPlayingButton
• Tested on CarPlay simulator (I/O → External Displays → CarPlay)
• Tested in real vehicle (if available)
• Tested both with and without debugger attached

Resources

WWDC: 2022-110338, 2017-251, 2019-501

Docs: /mediaplayer/mpnowplayinginfocenter, /mediaplayer/mpremotecommandcenter, /mediaplayer/mpnowplayingsession

Skills: axiom-avfoundation-ref, axiom-now-playing-carplay, axiom-now-playing-musickit

Last Updated: 2026-01-04 Status: iOS 18+ discipline skill covering Now Playing, CarPlay, and MusicKit integration Tested: Based on WWDC 2019-501, WWDC 2022-110338 patterns