Swift Resume Audio AVFoundation - AVQueuePlayer AVPlayer

ViewController.swift

import UIKit
import AVFoundation

var player: AVQueuePlayer!

class ViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, withOptions: AVAudioSessionCategoryOptions.MixWithOthers )
            try AVAudioSession.sharedInstance().setActive(true, withOptions: .NotifyOthersOnDeactivation)
        } catch { print("initial crapped out")}
        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("Interruption began")
                        player.pause()
                        
                    case .Ended:
                        print("Interruption ended")
                       _ = NSTimer.scheduledTimerWithTimeInterval(0.5, target: self, selector: "resumeNow:", userInfo: nil, repeats: false)
                    }
                }
        }
    }
    func resumeNow(timer : NSTimer) {
        print("Attempting restart")
        do {
            try AVAudioSession.sharedInstance().setActive(true)
        } catch {
            print("It crapped out")
            print(error)
        }
        player.play()
        
    }
}

you should use notification center callback

NotificationCenter.default.addObserver(self, selector: #selector(enteredBackground), name: UIApplication.didEnterBackgroundNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(enteredForeground), name: UIApplication.willEnterForegroundNotification, object: nil)


  @objc func enteredBackground() {
        playerController.player?.pause()
    }

    @objc func enteredForeground() {
       playerController.player?.play()
    }

work for me: https://stackoverflow.com/questions/54971492/how-can-i-resume-the-mp4-video-after-transition-from-the-background-to-the-activ