Add an AudioPlayerRateManager implementation for iOS 16+.

ios/App/Shared/player/AudioPlayer.swift

@@ -62,7 +62,12 @@ class AudioPlayer: NSObject {
         self.audioPlayer.automaticallyWaitsToMinimizeStalling = true
         self.sessionId = sessionId
         self.status = .uninitialized
-        self.rateManager = LegacyAudioPlayerRateManager(audioPlayer: self.audioPlayer, defaultRate: playbackRate)
+        
+        if #available(iOS 16.0, *) {
+            self.rateManager = DefaultedAudioPlayerRateManager(audioPlayer: self.audioPlayer, defaultRate: playbackRate)
+        } else {
+            self.rateManager = LegacyAudioPlayerRateManager(audioPlayer: self.audioPlayer, defaultRate: playbackRate)
+        }
         
         super.init()
         

ios/App/Shared/player/DefaultedAudioPlayerRateManager.swift

@@ -0,0 +1,94 @@
+//
+//  DefaultedAudioPlayerRateManager.swift
+//  Audiobookshelf
+//
+//  Created by Marke Hallowell on 4/14/24.
+//
+
+import Foundation
+import AVFoundation
+
+@available(iOS 16.0, *)
+class DefaultedAudioPlayerRateManager: NSObject, AudioPlayerRateManager {
+    internal let logger = AppLogger(category: "DefaultedAudioPlayerRateManager")
+    
+    internal var audioPlayer: AVPlayer
+    
+    // MARK: - AudioPlayerRateManager
+    public private(set) var defaultRate: Float
+    public private(set) var rate: Float
+    public var rateChangedCompletion: () -> Void
+    public var defaultRateChangedCompletion: () -> Void
+
+    required init(audioPlayer: AVPlayer, defaultRate: Float) {
+        self.audioPlayer = audioPlayer
+        self.rateChangedCompletion = {}
+        self.defaultRateChangedCompletion = {}
+        self.rate = self.audioPlayer.rate
+        self.defaultRate = defaultRate
+        self.audioPlayer.defaultRate = defaultRate
+
+        super.init()
+        
+        NotificationCenter.default.addObserver(self, selector: #selector(handleObservedRateChange), name: AVPlayer.rateDidChangeNotification, object: self.audioPlayer)
+    }
+    
+    public func setPlaybackRate(_ rate: Float) {
+        self.handlePlaybackRateChange(rate, observed: false)
+    }
+    
+    // No-op (player automatically resumes at last-known defaultRate)
+    public func handlePlayEvent() { }
+    
+    // MARK: - Destructor
+    public func destroy() {
+        NotificationCenter.default.removeObserver(self, name: AVPlayer.rateDidChangeNotification, object: self.audioPlayer)
+    }
+    
+    // MARK: - Internal
+    internal func handlePlaybackRateChange(_ rate: Float, observed: Bool = false) {
+        let playbackSpeedChanged = rate > 0.0 && rate != self.defaultRate
+        
+        if playbackSpeedChanged {
+            self.defaultRate = rate
+            self.audioPlayer.defaultRate = rate
+            self.defaultRateChangedCompletion()
+
+            // Check to see if we also need to make a temporary rate change to player
+            if self.audioPlayer.rate > 0.0 {
+                if self.audioPlayer.rate != rate {
+                    self.rate = rate
+                    self.audioPlayer.rate = rate
+                    self.rateChangedCompletion()
+                }
+            }
+        } else {
+            self.rate = rate
+            self.rateChangedCompletion()
+        }
+    }
+    
+    // MARK: - iOS rate change notification handler
+    @objc internal func handleObservedRateChange(notification: Notification) {
+        // TODO: Consider handling cases individually (e.g. overall session impact?)
+        /*
+        guard let reason = notification.userInfo?[AVPlayer.rateDidChangeReasonKey] as? AVPlayer.RateDidChangeReason else {
+            return
+        }
+         
+        switch reason {
+        case .appBackgrounded:
+            // App transitioned to the background.
+        case .audioSessionInterrupted:
+            // The system interrupts the app's audio session.
+        case .setRateCalled:
+            // The app set the player's rate.
+        case .setRateFailed:
+            // An attempt to change the player's rate failed.
+        default:
+            break
+        }
+        */
+        self.handlePlaybackRateChange(self.audioPlayer.rate, observed: true)
+    }
+}