AVAudioSession Interrupts and Route Changes

Question

I am developing a game that includes a background audio player running in the background. When you deal with pausing all tracks, and then resuming when you press the pause button, I did not find any significant difficulties:

class AudioMultiTrack {

var tracks     : [AudioTrack]
var mixer      : AVAudioMixerNode
var pauseTime  : AVAudioTime?

var engine     = AVAudioEngine()
var volumes    = [Float]()

init(audioTracks: [AudioTrack]){
    tracks = audioTracks
    mixer = engine.mainMixerNode
}

func initialize() {
    for track in tracks {
        track.setUpTrack()
        engine.attach(track.audioPlayer)
        engine.connect(track.audioPlayer, to: mixer, format: track.format)
        track.scheduleFile()
    }

    do {
        try engine.start()
    } catch {
        fatalError("error starting engine")
    }
}

func play() {
    for track in tracks {
        track.audioPlayer.play(at: startTime())
    }
}

func pause() {
    pauseTime = tracks[0].audioPlayer.lastRenderTime

    for track in tracks {
        track.audioPlayer.pause()
    }

}

func unPause() {

    for track in tracks {
        track.scheduleFile()
        track.audioPlayer.play(at: pauseTime)
    }
}

func stop() {
    pauseTime = tracks[0].audioPlayer.lastRenderTime
    engine.stop()

    for track in tracks {
        engine.detach(track.audioPlayer)
    }

    engine.reset()
}

func startTime() ->AVAudioTime {
    let sampleRate = tracks[0].format.sampleRate
    let sampleTime = AVAudioFramePosition(sampleRate)

    return AVAudioTime(sampleTime: sampleTime, atRate: sampleRate)
}

When a pause is pressed in the GameViewController:

func pausePressed() {
   audio.pause()
}

func continuePressed() {
   audio.unPause()
}

However, when considering interruptions or route changes in this way:

    func handleInterruption(notification: NSNotification) {
    guard let info = notification.userInfo else { return }

    switch info[AVAudioSessionInterruptionTypeKey] as! Int {
    case 0:
        audio.unPause()
    case 1:
        audio.pause()
    default:
        break;
    }
}

The program crashes, and I get:

*** Application termination due to the uncaught exception "com.apple.coreaudio.avfaudio", reason: "prerequisite is false: _engine-> IsRunning ()"

So, it looks like the sound engine is stopping, and I don't want to reinitialize the audio player for a number of reasons, including setup time and game continuity ...

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Answer 1

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