Using Swift to display title of currently playing .MP3

you need to add the import statement for Media player and set the General Media Item Property Keys for nowPlayingInfo property. For the MPMediaItemPropertyArtwork you need to take a look at this MPMediaItemArtwork

import MediaPlayer

let audioInfo = MPNowPlayingInfoCenter.defaultCenter()
let audioName = audioPath.lastPathComponent!.stringByDeletingPathExtension
audioInfo.nowPlayingInfo = [ MPMediaItemPropertyTitle: audioName, MPMediaItemPropertyArtist:"artistName"]

To extract the metadata from your mp3 you need to create an AVPlayerItem and access its asset commonMetadata property

let playerItem = AVPlayerItem(URL: audioPath)
let metadataList = playerItem.asset.commonMetadata as! [AVMetadataItem]
for item in metadataList {
    if item.commonKey == "title" {
        println("Title = " + item.stringValue)
    }
    if item.commonKey == "artist" {
        println("Artist = " + item.stringValue)
    }
}       

Note: You will have to invoke beginReceivingRemoteControlEvents() otherwise it will not work on the actual device.

override func viewDidLoad() {
    super.viewDidLoad()
    UIApplication.sharedApplication().beginReceivingRemoteControlEvents()
}