AVAudioPlayer produces lag despite prepareToPlay() in Swift

Question

Playing a very short sound (~0.5s) produces a hiccup (like a lag) in my SpriteKit iOS game programmed in Swift. In other questions, I read that I should prepareToPlay() the sound, which I did.

I even used a variable (soundReady) to check if the sound is prepared before playing it. I also re-prepare the sound whenever it is finished playing (audioPlayerDidFinishPlaying()). Here are the relevant parts of the code:

class GameScene: SKScene, AVAudioPlayerDelegate {

   var splashSound = NSURL()
   var audioPlayer = AVAudioPlayer()
   var soundReady = false

   override func didMoveToView(view: SKView) {
      let path = NSBundle.mainBundle().pathForResource("plopSound", ofType: "m4a")
      splashSound = NSURL(fileURLWithPath: path)
      audioPlayer = AVAudioPlayer(contentsOfURL: splashSound, error: nil)
      audioPlayer.delegate = self
      soundReady = audioPlayer.prepareToPlay()
   }

   func playSound(){
      if(soundReady){
         audioPlayer.play()
         soundReady = false
      }
   }

   func audioPlayerDidFinishPlaying(player: AVAudioPlayer!, successfully flag: Bool){
      //Prepare to play after Sound finished playing
      soundReady = audioPlayer.prepareToPlay()
   }
}

I have no idea where I've gone wrong on this one. I feel like I have tried everything (including, but not limited to: only preparing once, preparing right after playing, not using a variable, but just prepareToPlay()).

Additional information:

• The sound plays without delay.
• How quickly the sound is played after the last finish does not seem to impact the lag.

Answer 1

I ran into this same problem and played the sound in the backgroundQueue.

This is a good example: https://stackoverflow.com/a/25070476/586204.

let qualityOfServiceClass = QOS_CLASS_BACKGROUND
let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)
dispatch_async(backgroundQueue, {
    audioPlayer.play()
})