AVAudioPlayer smart speed to speed up playback during quiet periods in an audio file

ExampleViewController.swift

//
//  ExampleViewController.swift
//  podcast-ios
//
//  Created by Dennis Fedorko on 3/19/17.
//  Copyright © 2017 Dennis Fedorko. All rights reserved.
//

import UIKit
import AVFoundation

class ExampleViewController: UIViewController {
    
    var player: AVAudioPlayer!
    var amplitudes: [Float] = []

    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .white
                
    }
    
    // Tap screen to start playback
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let _ = try? AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback),
            let _ = try? AVAudioSession.sharedInstance().setActive(true) else { return }
        
        player = try! AVAudioPlayer(contentsOf: URL(fileURLWithPath: Bundle.main.path(forResource: "test", ofType: "mp3")!))
        player.prepareToPlay()
        player.addObserver(self, forKeyPath: "rate", options: .new, context: nil)
        player.isMeteringEnabled = true
        player.enableRate = true
        player.play()
        
        
        var timeElapsed = 0.0
        
        Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { (Timer) in
            
            timeElapsed += 0.1
            
            self.player.updateMeters()
            self.amplitudes.append(self.player.averagePower(forChannel: 0) + 120.0)
            
            print("--------")
            print("min: \(self.amplitudes.min()!)")
            print("max: \(self.amplitudes.max()!)")
            print("current: \(self.amplitudes.last!)")
            print("--------")
            
            if self.amplitudes.last! > 50 {
                self.player.rate = 1.0 + (self.amplitudes.max()! - self.amplitudes.last!) * 0.01
            } else {
                self.player.rate = 1.0 + (self.amplitudes.max()! - self.amplitudes.last!) * 0.02
            }
            
            print("timeElapsed: \(timeElapsed)")
            print("playerTimeElapsed: \(self.player.currentTime)")
        }
    }
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        
        if keyPath == "rate" {
            print(player.rate)
        }
        
    }


}

To see example work just add to an xcodeproj project, drop in any mp3 file named "test.mp3" to the project, add as rootViewController for window and run the app.

When the view controller is on screen, tap the screen to run the demo.