AVAudioEngine crashes when I unplug headphones during a call

Question

Here is what I see in the log:

16:33:20.236: Call is Dialing
16:33:21.088: AVAudioSessionInterruptionNotification
16:33:21.450: AVAudioSessionRouteChangeNotification
16:33:21.450: ....change reason CategoryChange
16:33:21.539: AVAudioEngineConfigurationChangeNotification
16:33:21.542: Starting Audio Engine
16:33:23.863: AVAudioSessionRouteChangeNotification
16:33:23.863: ....change reason OldDeviceUnavailable
16:33:23.860 ERROR:     [0x100a70000] AVAudioIONodeImpl.mm:317: ___ZN13AVAudioIOUnit11GetHWFormatEjPj_block_invoke: required condition is false: hwFormat
*** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: hwFormat'

I've subscribed for both AVAudioEngineConfigurationChangeNotification, AVAudioSessionInterruptionNotification:

@objc private func handleAudioEngineConfigurationChangeNotification(notification: NSNotification) {
    println2(notification.name)
    makeEngineConnections()
    startEngine()
}

@objc private func handleAudioSessionInterruptionNotification(notification: NSNotification) {
    println2(notification.name)
    if let interruptionType = AVAudioSessionInterruptionType(rawValue: notification.userInfo?[AVAudioSessionInterruptionTypeKey] as! UInt) {
        switch interruptionType {
        case .Began:
            audioPlayerNode.stop()
        case .Ended:
            if let interruptionOptionValue = notification.userInfo?[AVAudioSessionInterruptionOptionKey] as? UInt {
                let interruptionOption = AVAudioSessionInterruptionOptions(interruptionOptionValue)
                if interruptionOption == AVAudioSessionInterruptionOptions.OptionShouldResume {
                    AVAudioSession.sharedInstance().setActive(true, error: nil)
                    startEngine()
                }
            }
        }
    }
}

func startEngine() {
    println2("Starting Audio Engine")
    var error: NSError?

    if !audioEngine.running {
        audioEngine.startAndReturnError(&error)
        if let error = error {
            println2("Error initializing Audio Engine: " + error.localizedDescription)
        }
    }
}

private func makeEngineConnections() {
    let mainMixer = audioEngine.mainMixerNode
    audioEngine.connect(audioPlayerNode, to: audioEqNode, format: mainMixer.outputFormatForBus(0))
    audioEngine.connect(audioEqNode, to: audioTimePitch, format: mainMixer.outputFormatForBus(0))
    audioEngine.connect(audioTimePitch, to: mainMixer, format: mainMixer.outputFormatForBus(0))
}

but it doesn't seem working.

How to avoid this crash?

Answer 1

I suspect the problem is here:
audioEngine.connect(audioTimePitch, to: mainMixer, format: mainMixer.outputFormatForBus(0))

The documentation says:

This method calls connect:to:fromBus:toBus:format: using bus 0 for the source audio node, and bus 0 for the destination audio node, except in the case of a destination which is a mixer, in which case the destination is the mixer’s nextAvailableInputBus.