Estoy siguiendo instruccionesaquí, Armé este proyecto de prueba para manejar las interrupciones en la reproducción de audio. Específicamente, estoy usando la alarma de la aplicación de reloj de iPhone predeterminada como interrupción. Parece que se llama al manejador de interrupciones pero no se supera ellet = interruptionType línea como "Tipo incorrecto"apareció dos veces.

import UIKit
import AVFoundation

class ViewController: UIViewController {

    var player = AVAudioPlayer()

    let audioPath = NSBundle.mainBundle().pathForResource("rachmaninov-romance-sixhands-alianello", ofType: "mp3")!

    func handleInterruption(notification: NSNotification) {

        guard let interruptionType = notification.userInfo?[AVAudioSessionInterruptionTypeKey] as? AVAudioSessionInterruptionType else { print("wrong type"); return }

        switch interruptionType {

        case .Began:
            print("began")
            // player is paused and session is inactive. need to update UI)
            player.pause()
            print("audio paused")

        default:
            print("ended")
            /**/
            if let option = notification.userInfo?[AVAudioSessionInterruptionOptionKey] as? AVAudioSessionInterruptionOptions where option == .ShouldResume {
                // ok to resume playing, re activate session and resume playing
                // need to update UI
                player.play()
                print("audio resumed")
            }
            /**/
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        do {
            try player = AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: audioPath))
            player.numberOfLoops = -1 // play indefinitely
            player.prepareToPlay()
            //player.delegate = player

        } catch {
            // process error here
        }

        // enable play in background https://stackoverflow.com/a/30280699/1827488 but this audio still gets interrupted by alerts
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
            print("AVAudioSession Category Playback OK")
            do {
                try AVAudioSession.sharedInstance().setActive(true)
                print("AVAudioSession is Active")
            } catch let error as NSError {
                print(error.localizedDescription)
            }
        } catch let error as NSError {
            print(error.localizedDescription)
        }

        // add observer to handle audio interruptions
        // using 'object: nil' does not have a noticeable effect
        let theSession = AVAudioSession.sharedInstance()
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.handleInterruption(_:)), name: AVAudioSessionInterruptionNotification, object: theSession)

        // start playing audio
        player.play()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

Además, siguiendo una ideaaquí, He modificado el controlador para

func handleInterruption(notification: NSNotification) {

        //guard let interruptionType = notification.userInfo?[AVAudioSessionInterruptionTypeKey] as? AVAudioSessionInterruptionType else { print("wrong type"); return }

        if notification.name != AVAudioSessionInterruptionNotification
            || notification.userInfo == nil{
            return
        }

        var info = notification.userInfo!
        var intValue: UInt = 0
        (info[AVAudioSessionInterruptionTypeKey] as! NSValue).getValue(&intValue)
        if let interruptionType = AVAudioSessionInterruptionType(rawValue: intValue) {

            switch interruptionType {

            case .Began:
                print("began")
                // player is paused and session is inactive. need to update UI)
                player.pause()
                print("audio paused")

            default:
                print("ended")
                /** /
                if let option = notification.userInfo?[AVAudioSessionInterruptionOptionKey] as? AVAudioSessionInterruptionOptions where option == .ShouldResume {
                    // ok to resume playing, re activate session and resume playing
                    // need to update UI
                    player.play()
                    print("audio resumed")
                }
                / **/
                player.play()
                print("audio resumed")
            }
        }
    }

Los resultados son que todo "comenzó", "audio en pausa", "finalizó" y "audio reanudado" se muestra en la consola, pero la reproducción de audio no se reanuda.

Nota: moví elplayer.play() fuera del comentadowhere option == .ShouldResume si la declaración porque esoif la condición no es verdadera cuando el.Ended Se produce interrupción.