如何跟踪iOS中的音轨进展？

Question

I'm building a podcast playing app that fetches its mp3 URL from a parsed RSS feed. I'm using AVPlayer to play the file without issue, but I'd like to figure out how to keep track of the progression of the track for various reasons (updating the value of the progress slider, saving the last spot the track was on when it was stopped so that hitting play doesn't restart the audio...)

This is what I've got so far, and through my research I'm just not sure how to go about doing this. The RSS feed does give me iTunes:Duration (01:24:20 for example) if that helps.

    @IBAction func playPauseButtonPressed(sender: UIButton) {

    if playPauseButton.titleLabel!.text == "Play" {
        playPauseButton.setTitle("Pause", forState: .Normal)
        let playerItem = AVPlayerItem(URL: trackURL!)
        audioPlayer = AVPlayer(playerItem: playerItem)
        audioPlayer.rate = 1.0
        audioPlayer.play()
    } else {
        playPauseButton.setTitle("Play", forState: .Normal)
        audioPlayer.pause()
    }
}

Answer 1

Assuming you've declared and constrained a progress view properly:`

let total = audioPlayer.duration
let f = audioPlayer.currentTime / total;
let w = view.frame.width * CGFloat(f)

Then use w as the width of your view.