Fix AVCaptureSession race condition.

Sources/Extension/AVCaptureSession+Extension.swift

@@ -1,13 +1,13 @@
 import AVFoundation
 import Foundation
 
+// swiftlint:disable unused_setter_value
 #if targetEnvironment(macCatalyst)
 extension AVCaptureSession {
     var isMultitaskingCameraAccessSupported: Bool {
         get {
             false
         }
-        // swiftlint:disable unused_setter_value
         set {
             logger.warn("isMultitaskingCameraAccessSupported is unavailabled in Mac Catalyst.")
         }
@@ -17,10 +17,27 @@ extension AVCaptureSession {
         get {
             false
         }
-        // swiftlint:disable unused_setter_value
         set {
             logger.warn("isMultitaskingCameraAccessEnabled is unavailabled in Mac Catalyst.")
         }
     }
 }
+#else
+extension AVCaptureSession {
+    @available(iOS, obsoleted: 16.0)
+    var isMultitaskingCameraAccessEnabled: Bool {
+        get {
+            false
+        }
+        set {
+            logger.warn("isMultitaskingCameraAccessEnabled is unavailabled in under iOS 16.")
+        }
+    }
+
+    @available(iOS, obsoleted: 16.0)
+    var isMultitaskingCameraAccessSupported: Bool {
+        false
+    }
+}
 #endif
+// swiftlint:enable unused_setter_value

Sources/Media/IOMixer.swift

@@ -19,7 +19,6 @@ protocol IOMixerDelegate: AnyObject {
     func mixer(_ mixer: IOMixer, sessionWasInterrupted session: AVCaptureSession, reason: AVCaptureSession.InterruptionReason)
     func mixer(_ mixer: IOMixer, sessionInterruptionEnded session: AVCaptureSession, reason: AVCaptureSession.InterruptionReason)
     #endif
-    func mixerSessionWillResume(_ mixer: IOMixer)
 }
 
 /// An object that mixies audio and video for streaming.
@@ -77,6 +76,26 @@ public class IOMixer {
         }
     }
 
+    var inBackgroundMode = false {
+        didSet {
+            guard inBackgroundMode != oldValue else {
+                return
+            }
+            if inBackgroundMode {
+                if !session.isMultitaskingCameraAccessEnabled {
+                    videoIO.multiCamCapture.detachSession(session)
+                    videoIO.capture.detachSession(session)
+                }
+            } else {
+                startCaptureSessionIfNeeded()
+                if !session.isMultitaskingCameraAccessEnabled {
+                    videoIO.capture.attachSession(session)
+                    videoIO.multiCamCapture.attachSession(session)
+                }
+            }
+        }
+    }
+
     private var readyState: ReadyState = .standby
     private(set) lazy var audioEngine: AVAudioEngine? = {
         return IOMixer.audioEngineHolder.retain()
@@ -218,7 +237,7 @@ public class IOMixer {
         if session.canSetSessionPreset(sessionPreset) {
             session.sessionPreset = sessionPreset
         }
-        if #available(iOS 16.0, *), isMultitaskingCameraAccessEnabled, session.isMultitaskingCameraAccessSupported {
+        if isMultitaskingCameraAccessEnabled && session.isMultitaskingCameraAccessSupported {
             session.isMultitaskingCameraAccessEnabled = true
         }
         return session
@@ -303,10 +322,6 @@ extension IOMixer: Running {
         guard !isRunning.value else {
             return
         }
-        #if os(iOS)
-        NotificationCenter.default.addObserver(self, selector: #selector(didEnterBackground(_:)), name: UIApplication.didEnterBackgroundNotification, object: nil)
-        NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground(_:)), name: UIApplication.willEnterForegroundNotification, object: nil)
-        #endif
         addSessionObservers(session)
         session.startRunning()
         isRunning.mutate { $0 = session.isRunning }
@@ -318,14 +333,13 @@ extension IOMixer: Running {
         }
         removeSessionObservers(session)
         session.stopRunning()
-        #if os(iOS)
-        NotificationCenter.default.removeObserver(self, name: UIApplication.didEnterBackgroundNotification, object: nil)
-        NotificationCenter.default.removeObserver(self, name: UIApplication.willEnterForegroundNotification, object: nil)
-        #endif
         isRunning.mutate { $0 = session.isRunning }
     }
 
-    func startCaptureSession() {
+    func startCaptureSessionIfNeeded() {
+        guard isRunning.value && !session.isRunning else {
+            return
+        }
         session.startRunning()
         isRunning.mutate { $0 = session.isRunning }
     }
@@ -387,7 +401,7 @@ extension IOMixer: Running {
             }
         #if os(iOS)
         case .mediaServicesWereReset:
-            resumeCaptureSessionIfNeeded()
+            startCaptureSessionIfNeeded()
         #endif
         default:
             break
@@ -416,37 +430,7 @@ extension IOMixer: Running {
         }
         delegate?.mixer(self, sessionInterruptionEnded: session, reason: reason)
     }
-
-    @objc
-    private func didEnterBackground(_ notification: Notification) {
-        if #available(iOS 16, *) {
-            guard !session.isMultitaskingCameraAccessEnabled else {
-                return
-            }
-        }
-        videoIO.multiCamCapture.detachSession(session)
-        videoIO.capture.detachSession(session)
-    }
-
-    @objc
-    private func willEnterForeground(_ notification: Notification) {
-        resumeCaptureSessionIfNeeded()
-        if #available(iOS 16, *) {
-            guard !session.isMultitaskingCameraAccessEnabled else {
-                return
-            }
-        }
-        videoIO.capture.attachSession(session)
-        videoIO.multiCamCapture.attachSession(session)
-    }
     #endif
-
-    private func resumeCaptureSessionIfNeeded() {
-        guard isRunning.value && !session.isRunning else {
-            return
-        }
-        delegate?.mixerSessionWillResume(self)
-    }
 }
 #else
 extension IOMixer: Running {

Sources/Net/NetStream.swift

@@ -168,6 +168,15 @@ open class NetStream: NSObject {
         }
     }
 
+    /// Creates a NetStream object.
+    override public init() {
+        super.init()
+        #if os(iOS)
+        NotificationCenter.default.addObserver(self, selector: #selector(didEnterBackground(_:)), name: UIApplication.didEnterBackgroundNotification, object: nil)
+        NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground(_:)), name: UIApplication.willEnterForegroundNotification, object: nil)
+        #endif
+    }
+
     #if os(iOS) || os(macOS)
     /// Attaches the primary camera object.
     /// - Warning: This method can't use appendSampleBuffer at the same time.
@@ -284,6 +293,21 @@ open class NetStream: NSObject {
     public func stopRecording() {
         mixer.recorder.stopRunning()
     }
+
+    #if os(iOS)
+    @objc
+    private func didEnterBackground(_ notification: Notification) {
+        // Require main thread. Otherwise the microphone cannot be used in the background.
+        mixer.inBackgroundMode = true
+    }
+
+    @objc
+    private func willEnterForeground(_ notification: Notification) {
+        lockQueue.async {
+            self.mixer.inBackgroundMode = false
+        }
+    }
+    #endif
 }
 
 extension NetStream: IOMixerDelegate {
@@ -296,12 +320,6 @@ extension NetStream: IOMixerDelegate {
         delegate?.stream(self, didOutput: audio, presentationTimeStamp: presentationTimeStamp)
     }
 
-    func mixerSessionWillResume(_ mixer: IOMixer) {
-        lockQueue.async {
-            mixer.startCaptureSession()
-        }
-    }
-
     #if os(iOS)
     func mixer(_ mixer: IOMixer, sessionWasInterrupted session: AVCaptureSession, reason: AVCaptureSession.InterruptionReason) {
         delegate?.stream(self, sessionWasInterrupted: session, reason: reason)