Implement lazy AVAudioSession activation on iOS (#268)

Author: alexlapa

CHANGELOG.md

@@ -29,6 +29,7 @@ All user visible changes to this project will be documented in this file. This p
 
 - Upgraded [libwebrtc] to [142.0.7444.175] version. ([#256], [#254], [#248], [#260], [#264], [todo])
 - Removed camera permission request in `enumerateDevices()` on Android. ([#258])
+- `AVAudioSession` is now captured only when there is at least one `PeerConnection` or local audio track, and released when there are none. ([#268])
 
 ### Fixed
 
@@ -51,6 +52,7 @@ All user visible changes to this project will be documented in this file. This p
 [#263]: https://github.com/instrumentisto/medea-flutter-webrtc/pull/263
 [#264]: https://github.com/instrumentisto/medea-flutter-webrtc/pull/264
 [#265]: https://github.com/instrumentisto/medea-flutter-webrtc/pull/265
+[#268]: https://github.com/instrumentisto/medea-flutter-webrtc/pull/268
 [todo]: https://github.com/instrumentisto/medea-flutter-webrtc/commit/todo
 [142.0.7444.175]: https://github.com/instrumentisto/libwebrtc-bin/releases/tag/142.0.7444.175
 

example/ios/Podfile.lock

@@ -27,8 +27,8 @@ EXTERNAL SOURCES:
 SPEC CHECKSUMS:
   Flutter: cabc95a1d2626b1b06e7179b784ebcf0c0cde467
   instrumentisto-libwebrtc-bin: 06422ba9bf8b5ec14f25c1dda10109e4021decec
-  integration_test: 4a889634ef21a45d28d50d622cf412dc6d9f586e
-  medea_flutter_webrtc: b3379af53010e6d4bd45023ba64d59864117c2fc
+  integration_test: 252f60fa39af5e17c3aa9899d35d908a0721b573
+  medea_flutter_webrtc: 90f34d3480bf89ebe1699c3091795b6a0ac1c2ae
 
 PODFILE CHECKSUM: 96cbd66feeeb9e49d88210ea2b661316b312dda7
 

ios/Classes/MedeaFlutterWebrtcPlugin.swift

@@ -20,11 +20,12 @@ public class MedeaFlutterWebrtcPlugin: NSObject, FlutterPlugin {
     self.state = State()
     self.messenger = messenger
     self.textures = textures
+    let mediaDevices = MediaDevices(state: self.state)
     self.peerConnectionFactory = PeerConnectionFactoryController(
-      messenger: self.messenger, state: self.state
+      messenger: self.messenger, state: self.state, mediaDevices: mediaDevices
     )
     self.mediaDevices = MediaDevicesController(
-      messenger: self.messenger, mediaDevices: MediaDevices(state: self.state)
+      messenger: self.messenger, mediaDevices: mediaDevices
     )
     self.videoRendererFactory = VideoRendererFactoryController(
       messenger: self.messenger, registry: self.textures

ios/Classes/MediaDevices.swift

@@ -9,16 +9,20 @@ class MediaDevices {
   /// Subscribers for `onDeviceChange` callback of these `MediaDevices`.
   private var onDeviceChange: [() -> Void] = []
 
+  /// Set of all existing `RTCPeerConnection`s.
+  private var activePeers: Set<Int> = []
+
+  /// Set of all existing local audio tracks.
+  private var activeAudioTracks: Set<String> = []
+
+  /// Indicator of whether `AVAudioSession` is currently "captured".
+  private var isAudioSessionActive: Bool = false
+
   /// Initializes new `MediaDevices` with the provided `State`.
   ///
   /// Subscribes on `AVAudioSession.routeChangeNotification` notifications for
   /// `onDeviceChange` callback firing.
   init(state: State) {
-    try? AVAudioSession.sharedInstance().setCategory(
-      AVAudioSession.Category.playAndRecord,
-      options: AVAudioSession.CategoryOptions.allowBluetooth
-    )
-    try? AVAudioSession.sharedInstance().setActive(true)
     self.state = state
     NotificationCenter.default.addObserver(
       forName: AVAudioSession.routeChangeNotification, object: nil,
@@ -31,6 +35,77 @@ class MediaDevices {
     )
   }
 
+  /// Called when a new `RTCPeerConnection` is created.
+  ///
+  /// Captures the `AVAudioSession` (if its not captured already).
+  func peerAdded(_ id: Int) {
+    assert(Thread.isMainThread)
+
+    self.activePeers.insert(id)
+    self.updateAudioSession()
+  }
+
+  /// Called when a `RTCPeerConnection` is disposed.
+  ///
+  /// Releases the `AVAudioSession` if it's the last `RTCPeerConnection` and
+  /// there are no active local audio tracks.
+  func peerRemoved(_ id: Int) {
+    assert(Thread.isMainThread)
+
+    if self.activePeers.remove(id) != nil {
+      self.updateAudioSession()
+    }
+  }
+
+  /// Called when a new local audio track is created.
+  ///
+  /// Captures the `AVAudioSession` (if its not captured already).
+  func audioTrackAdded(_ id: String) {
+    assert(Thread.isMainThread)
+
+    self.activeAudioTracks.insert(id)
+    self.updateAudioSession()
+  }
+
+  /// Called when a local audio track is disposed.
+  ////
+  /// Releases the `AVAudioSession` if it's the last local audio track and there
+  /// are no `RTCPeerConnection`s.
+  func audioTrackRemoved(_ id: String) {
+    assert(Thread.isMainThread)
+
+    if self.activeAudioTracks.remove(id) != nil {
+      self.updateAudioSession()
+    }
+  }
+
+  /// Captures the `AVAudioSession` if there is at least one local audio track
+  /// or `RTCPeerConnection`, or releases otherwise.
+  ///
+  /// No-op if the `AVAudioSession` is in the desired state already.
+  private func updateAudioSession() {
+    assert(Thread.isMainThread)
+
+    let shouldBeActive = !self.activePeers.isEmpty || !self.activeAudioTracks
+      .isEmpty
+    if shouldBeActive, !self.isAudioSessionActive {
+      try? AVAudioSession.sharedInstance().setCategory(
+        AVAudioSession.Category.playAndRecord,
+        options: AVAudioSession.CategoryOptions.allowBluetooth
+      )
+      try? AVAudioSession.sharedInstance().setActive(true)
+      self.isAudioSessionActive = true
+    } else {
+      if self.isAudioSessionActive {
+        try? AVAudioSession.sharedInstance().setActive(
+          false,
+          options: .notifyOthersOnDeactivation
+        )
+        self.isAudioSessionActive = false
+      }
+    }
+  }
+
   /// Switches current input device to the iPhone's microphone.
   func setBuiltInMicAsInput() {
     if let routes = AVAudioSession.sharedInstance().availableInputs {
@@ -159,7 +234,12 @@ class MediaDevices {
       withTrackId: LocalTrackIdGenerator.shared.nextId()
     )
     let audioSource = AudioMediaTrackSourceProxy(track: track)
-    return audioSource.newTrack()
+    let trackProxy = audioSource.newTrack()
+    self.audioTrackAdded(trackProxy.id())
+    trackProxy.onStopped(cb: { [weak self] in
+      self?.audioTrackRemoved(trackProxy.id())
+    })
+    return trackProxy
   }
 
   /// Creates a video `MediaStreamTrackProxy` for the provided

ios/Classes/controller/PeerConnectionFactoryController.swift

@@ -12,14 +12,22 @@ class PeerConnectionFactoryController {
   private var channel: FlutterMethodChannel
 
   /// Initializes a new `PeerConnectionFactoryController` and
-  /// `PeerConnectionFactoryProxy` based on the provided `State`.
-  init(messenger: FlutterBinaryMessenger, state: State) {
+  /// `PeerConnectionFactoryProxy` based on the provided `State` and
+  /// `MediaDevices`.
+  init(
+    messenger: FlutterBinaryMessenger,
+    state: State,
+    mediaDevices: MediaDevices
+  ) {
     let channelName = ChannelNameGenerator.name(
       name: "PeerConnectionFactory",
       id: 0
     )
     self.messenger = messenger
-    self.peerFactory = PeerConnectionFactoryProxy(state: state)
+    self.peerFactory = PeerConnectionFactoryProxy(
+      state: state,
+      mediaDevices: mediaDevices
+    )
     self.channel = FlutterMethodChannel(
       name: channelName,
       binaryMessenger: messenger

ios/Classes/proxy/PeerConnectionFactoryProxy.swift

@@ -48,10 +48,14 @@ class PeerConnectionFactoryProxy {
   /// Underlying native factory object of this factory.
   private var factory: RTCPeerConnectionFactory
 
+  /// Instance of a `MediaDevices` manager.
+  private var mediaDevices: MediaDevices
+
   /// Initializes a new `PeerConnectionFactoryProxy` based on the provided
-  /// `State`.
-  init(state: State) {
+  /// `State` and `MediaDevices`.
+  init(state: State, mediaDevices: MediaDevices) {
     self.factory = state.getPeerFactory()
+    self.mediaDevices = mediaDevices
   }
 
   /// Returns sender capabilities of this factory.
@@ -86,18 +90,20 @@ class PeerConnectionFactoryProxy {
       delegate: peerObserver
     )
     let peerProxy = PeerConnectionProxy(id: id, peer: peer!)
+    self.mediaDevices.peerAdded(id)
+    peerProxy.onDispose = { [weak self] in
+      guard let self = self else { return }
+
+      self.peerObservers.removeValue(forKey: id)
+      self.mediaDevices.peerRemoved(id)
+    }
     peerObserver.setPeer(peer: peerProxy)
 
     self.peerObservers[id] = peerObserver
 
     return peerProxy
   }
 
-  /// Removes the specified `PeerObserver` from the `peerObservers`.
-  private func remotePeerObserver(id: Int) {
-    self.peerObservers.removeValue(forKey: id)
-  }
-
   /// Generates the next track ID.
   private func nextId() -> Int {
     self.lastPeerConnectionId += 1

ios/Classes/proxy/PeerConnectionProxy.swift

@@ -28,6 +28,9 @@ class PeerConnectionProxy {
   /// Last unique ID of `RtpTransceiverProxy`s.
   private var lastTransceiverId: Int = 0
 
+  /// Callback for notifying about `PeerConnectionProxy` disposal.
+  var onDispose: (() -> Void)?
+
   /// Initializes a new `PeerConnectionProxy` with the provided `peer` and `id`.
   init(id: Int, peer: RTCPeerConnection) {
     self.peer = peer
@@ -289,5 +292,6 @@ class PeerConnectionProxy {
       receiver.notifyRemoved()
     }
     self.receivers = [:]
+    self.onDispose?()
   }
 }