iOS
MPMediaPickerDelegate

import UIKit
import AVFoundation
import MediaPlayer

class ViewController: UIViewController, MPMediaPickerControllerDelegate {
    
    var avMusicPlayer: AVAudioPlayer!
    var mpMediapicker: MPMediaPickerController!
    var mediaItems = [MPMediaItem]()
    let currentIndex = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool){
        //What to do?
    }

    func mediaPicker(_ mediaPicker: MPMediaPickerController, didPickMediaItems mediaItemCollection: MPMediaItemCollection) {
        mediaItems = mediaItemCollection.items
        updatePlayer()
        self.dismiss(animated: true, completion: nil)
    }

    func updatePlayer(){
        let item = mediaItems[currentIndex]
        // DO-TRY-CATCH try to setup AVAudioPlayer with the path, if successful, sets up the AVMusicPlayer, and song values.
        if let path: NSURL = item.assetURL as NSURL? {
            do
            {
                avMusicPlayer = try AVAudioPlayer(contentsOf: path as URL)
                avMusicPlayer.enableRate = true
                avMusicPlayer.rate = 1.0
                avMusicPlayer.numberOfLoops = 0
                avMusicPlayer.currentTime = 0
            }
            catch
            {
                avMusicPlayer = nil
            }
        }
    }

    @IBAction func Play(_ sender: AnyObject) {
        //AVMusicPlayer.deviceCurrentTime
        avMusicPlayer.play()
    }

    @IBAction func Stop(_ sender: AnyObject) {
        avMusicPlayer.stop()
    }

    @IBAction func picker(_ sender: AnyObject) {
        mpMediapicker = MPMediaPickerController.self(mediaTypes:MPMediaType.music)
        mpMediapicker.allowsPickingMultipleItems = false
        mpMediapicker.delegate = self
        self.present(mpMediapicker, animated: true, completion: nil)
    }
    
}