How to resume background audio in Swift 2 / AVPlayer?

I am learning Swift as my first programming language.

I've struggled for many hours to resume background audio playback after interruption (eg call)

What should happen:

1. Audio keeps playing when app goes to background (works)
2. When interrupted by a call, get the notification for interruption began (works)
3. When call ends, get the notification for interruption ends (works)
4. Resume playing the audio (does NOT work - hear nothing)

Really appreciate any help! Thanks

Notes:

1. The app is registered for background audio and plays fine before interruption
2. I have tried with and without the time delay to resume playing - neither work

Code:

import UIKit
import AVFoundation

var player: AVQueuePlayer!

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
            try AVAudioSession.sharedInstance().setActive(true, withOptions: .NotifyOthersOnDeactivation)
        } catch { }
        let songNames = ["music"]
        let songs = songNames.map { AVPlayerItem(URL:
            NSBundle.mainBundle().URLForResource($0, withExtension: "mp3")!) }
        player = AVQueuePlayer(items: songs)

        let theSession = AVAudioSession.sharedInstance()
        NSNotificationCenter.defaultCenter().addObserver(self,
            selector:"playInterrupt:",
            name:AVAudioSessionInterruptionNotification,
            object: theSession)

        player.play()
    }

    func playInterrupt(notification: NSNotification) {

        if notification.name == AVAudioSessionInterruptionNotification
            && notification.userInfo != nil {

            var info = notification.userInfo!
            var intValue: UInt = 0
            (info[AVAudioSessionInterruptionTypeKey] as! NSValue).getValue(&intValue)
            if let type = AVAudioSessionInterruptionType(rawValue: intValue) {
                switch type {
                case .Began:
                    print("aaaaarrrrgggg you stole me")
                    player.pause()

                case .Ended:
                    let timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: "resumeNow:", userInfo: nil, repeats: false)
                }
            }
        }
    }
    func resumeNow(timer : NSTimer) {
        player.play()
        print("attempted restart")
    }
}

Finally got it!

Solution: added the mixable option by changing the setCategory line to be:

AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback,
                                            withOptions: .mixWithOthers )