fix(ios): keep multitasking camera access across capture sessions

ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCMediaStream.m

@@ -628,13 +628,19 @@ - (void)getUserVideo:(NSDictionary*)constraints
       [videoDevice unlockForConfiguration];
     }
 
+    __weak FlutterWebRTCPlugin* weakSelf = self;
     [self.videoCapturer startCaptureWithDevice:videoDevice
                                         format:selectedFormat
                                            fps:selectedFps
                              completionHandler:^(NSError* error) {
                                if (error) {
                                  NSLog(@"Start capture error: %@", [error localizedDescription]);
+                                 return;
                                }
+
+                               // This is a freshly created capture session, so it
+                               // starts without multitasking camera access.
+                               [weakSelf applyMultitaskingCameraAccessToCaptureSession];
                              }];
 
     NSString* trackUUID = [[NSUUID UUID] UUIDString];

ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterWebRTCPlugin.m

@@ -1149,6 +1149,8 @@ - (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
     BOOL enable = [argsMap[@"enable"] boolValue];
 
     [self enableMultitaskingCameraAccess:enable result:result];
+  } else if ([@"isIOSMultitaskingCameraAccessSupported" isEqualToString:call.method]) {
+    [self multitaskingCameraAccessSupported:result];
   } else if ([@"mediaStreamTrackHasTorch" isEqualToString:call.method]) {
     NSDictionary* argsMap = call.arguments;
     NSString* trackId = argsMap[@"trackId"];
@@ -2416,8 +2418,61 @@ - (void)mediaStreamTrackSetVideoEffects:(nonnull NSString*)trackId
   }
 }
 
+/// Applies the remembered multitasking camera access request to the capture
+/// session in use.
+///
+/// A capture session is created per `getUserMedia` call and starts without
+/// multitasking camera access, so the request is applied again every time one
+/// is created.
+- (void)applyMultitaskingCameraAccessToCaptureSession {
+#if !TARGET_OS_OSX
+  if (!self.multitaskingCameraAccessRequested) {
+    return;
+  }
+
+  if (@available(iOS 16.0, *)) {
+    AVCaptureSession* session = self.videoCapturer.captureSession;
+    if (session == nil || !session.isMultitaskingCameraAccessSupported ||
+        session.multitaskingCameraAccessEnabled) {
+      return;
+    }
+
+    @try {
+      [session beginConfiguration];
+      [session setMultitaskingCameraAccessEnabled:YES];
+      [session commitConfiguration];
+    } @catch (NSException* exception) {
+      NSLog(@"applyMultitaskingCameraAccessToCaptureSession: Exception occurred: %@ - %@",
+            exception.name, exception.reason);
+    }
+  }
+#endif
+}
+
+/// Reports whether the capture session in use supports camera access while
+/// multitasking, or nil when there is no capture session to ask.
+- (void)multitaskingCameraAccessSupported:(FlutterResult)result {
+#if TARGET_OS_OSX
+  result(@NO);
+#else
+  if (@available(iOS 16.0, *)) {
+    AVCaptureSession* session = self.videoCapturer.captureSession;
+    if (session == nil) {
+      result(nil);
+      return;
+    }
+
+    result(@(session.isMultitaskingCameraAccessSupported));
+  } else {
+    result(@NO);
+  }
+#endif
+}
+
 - (void)enableMultitaskingCameraAccess:(BOOL)enable result:(FlutterResult)result {
   @try {
+    self.multitaskingCameraAccessRequested = enable;
+
     AVCaptureSession* session = self.videoCapturer.captureSession;
     if (session == nil) {
       NSLog(@"enableMultitaskingCameraAccess: Capture session is nil.");

ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/include/stream_webrtc_flutter/FlutterWebRTCPlugin.h

@@ -90,6 +90,10 @@ typedef void (^CapturerStopHandler)(CompletionHandler _Nonnull handler);
 @property(nonatomic, strong) NSMutableDictionary<NSString*, NSNumber*>* _Nonnull pausedTrackVolumes;
 @property(nonatomic) BOOL isAudioPlayoutPaused;
 
+/// Whether camera access while multitasking was asked for. Remembered so that
+/// a capture session created afterwards is started with it applied.
+@property(nonatomic) BOOL multitaskingCameraAccessRequested;
+
 - (void)mediaStreamTrackSetVideoEffects:(nonnull NSString*)trackId
                                   names:(nonnull NSArray<NSString*>*)names;
 - (RTCMediaStream* _Nullable)streamForId:(NSString* _Nonnull)streamId
@@ -108,6 +112,7 @@ typedef void (^CapturerStopHandler)(CompletionHandler _Nonnull handler);
 - (RTCMediaStreamTrack* _Nullable)remoteTrackForId:(NSString* _Nonnull)trackId;
 
 - (BOOL)hasLocalAudioTrack;
+- (void)applyMultitaskingCameraAccessToCaptureSession;
 - (void)ensureAudioSession;
 - (void)deactiveRtcAudioSession;
 

lib/src/helper.dart

@@ -224,6 +224,14 @@ class Helper {
   static Future<bool> enableIOSMultitaskingCameraAccess(bool enable) =>
       IosAudioManagement.enableMultitaskingCameraAccess(enable);
 
+  /// Whether the capture session in use supports camera access while
+  /// multitasking (iOS only).
+  ///
+  /// Returns `null` when there is no capture session to ask, which is the case
+  /// until the camera is started.
+  static Future<bool?> isIOSMultitaskingCameraAccessSupported() =>
+      IosAudioManagement.isMultitaskingCameraAccessSupported();
+
   /// Trigger the iOS audio route selection UI (iOS only).
   static Future<void> triggeriOSAudioRouteSelectionUI() =>
       IosAudioManagement.triggerAudioRouteSelectionUI();

lib/src/native/ios/audio_management.dart

@@ -84,4 +84,20 @@ class IosAudioManagement {
           'enableMultitaskingCameraAccess is only supported for iOS');
     }
   }
+
+  /// Whether the capture session in use supports camera access while
+  /// multitasking (iOS only).
+  ///
+  /// Returns `null` when there is no capture session to ask, which is the case
+  /// until the camera is started.
+  static Future<bool?> isMultitaskingCameraAccessSupported() async {
+    if (WebRTC.platformIsIOS) {
+      return await WebRTC.invokeMethod(
+        'isIOSMultitaskingCameraAccessSupported',
+      );
+    } else {
+      throw Exception(
+          'isMultitaskingCameraAccessSupported is only supported for iOS');
+    }
+  }
 }

macos/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterWebRTCPlugin.m

@@ -975,6 +975,8 @@ - (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
     BOOL enable = [argsMap[@"enable"] boolValue];
 
     [self enableMultitaskingCameraAccess:enable result:result];
+  } else if ([@"isIOSMultitaskingCameraAccessSupported" isEqualToString:call.method]) {
+    [self multitaskingCameraAccessSupported:result];
   } else if ([@"mediaStreamTrackHasTorch" isEqualToString:call.method]) {
     NSDictionary* argsMap = call.arguments;
     NSString* trackId = argsMap[@"trackId"];
@@ -2151,6 +2153,10 @@ - (void)enableMultitaskingCameraAccess:(BOOL)enable result:(FlutterResult)result
   result(@NO);
 }
 
+- (void)multitaskingCameraAccessSupported:(FlutterResult)result {
+  result(@NO);
+}
+
 - (void)mediaStreamGetTracks:(NSString*)streamId result:(FlutterResult)result {
   RTCMediaStream* stream = [self streamForId:streamId peerConnectionId:@""];
   if (stream) {