Swift IOS : Get the title of current song playing

I would like to build an app that is able to get the name of what ever song is currently playing on the device (For example if I am using Spotify or any other player to play a song, the app should be able to get the title). The title should then just be stored in a variable.

I have not been successful in using nowPlayingInfo or MPMediaItemPropertyTitle.

Could someone please help me with this? This is the code that I have tried but I get an error:

Use of unresolved identifier 'playerItem'

for the line:

let metadataList = playerItem.asset.metadata as! [AVMetadataItem]

import UIKit
import MediaPlayer
import AVFoundation
class ViewController: UIViewController {


var url:NSURL!
let audioInfo = MPNowPlayingInfoCenter.default()
var nowPlayingInfo:[String:Any] = [:]
override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    print(url.path!)

    let metadataList = playerItem.asset.metadata as! [AVMetadataItem]
    for item in metadataList {
        if item.commonKey != nil && item.value != nil {
            if item.commonKey  == "title" {
                println(item.stringValue)
                nowPlayingInfo[MPMediaItemPropertyTitle] = item.stringValue
            }
            if item.commonKey   == "type" {
                println(item.stringValue)
                nowPlayingInfo[MPMediaItemPropertyGenre] = item.stringValue
            }
            if item.commonKey  == "albumName" {
                println(item.stringValue)
                nowPlayingInfo[MPMediaItemPropertyAlbumTitle] = item.stringValue
            }
            if item.commonKey   == "artist" {
                println(item.stringValue)
                nowPlayingInfo[MPMediaItemPropertyArtist] = item.stringValue
            }
            if item.commonKey  == "artwork" {
                if let image = UIImage(data: item.value as! NSData) {
                    nowPlayingInfo[MPMediaItemPropertyArtwork] = MPMediaItemArtwork(image: image)
                    println(image.description)
                }
            }
        }
    }
    audioInfo.nowPlayingInfo = nowPlayingInfo