[iOS] Fix incorrectly oriented frames when rapidly switching between cameras.

webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m

Index: webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m
diff --git a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m
index a2290c2458405a1d39458f64eae820abfdc14bc9..fb2ce547b0a7700d55bc6d324242336e2bfb6d1c 100644
--- a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m
+++ b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m
@@ -29,21 +29,26 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
 
 @interface RTCCameraVideoCapturer ()<AVCaptureVideoDataOutputSampleBufferDelegate>
 @property(nonatomic, readonly) dispatch_queue_t frameQueue;
+@property(assign) BOOL switchingCameras;
 @end
 
 @implementation RTCCameraVideoCapturer {
   AVCaptureVideoDataOutput *_videoDataOutput;
   AVCaptureSession *_captureSession;
   AVCaptureDevice *_currentDevice;
-  RTCVideoRotation _rotation;
   BOOL _hasRetriedOnFatalError;
   BOOL _isRunning;
   // Will the session be running once all asynchronous operations have been completed?
   BOOL _willBeRunning;
+  BOOL _switchingCameras;
+#if TARGET_OS_IPHONE
+  UIDeviceOrientation _orientation;
+#endif
 }
 
 @synthesize frameQueue = _frameQueue;
 @synthesize captureSession = _captureSession;
+@synthesize switchingCameras = _switchingCameras;
 
 - (instancetype)initWithDelegate:(__weak id<RTCVideoCapturerDelegate>)delegate {
   if (self = [super initWithDelegate:delegate]) {
@@ -55,7 +60,9 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
       return nil;
     }
     NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
+    self.switchingCameras = NO;
 #if TARGET_OS_IPHONE
+    _orientation = UIDeviceOrientationPortrait;
     [center addObserver:self
                selector:@selector(deviceOrientationDidChange:)
                    name:UIDeviceOrientationDidChangeNotification
@@ -117,7 +124,7 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
 - (void)startCaptureWithDevice:(AVCaptureDevice *)device
                         format:(AVCaptureDeviceFormat *)format
                            fps:(NSInteger)fps {
-  _willBeRunning = true;
+  _willBeRunning = YES;
   [RTCDispatcher
       dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
                     block:^{
@@ -136,17 +143,19 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
                         return;
                       }
 
+                      self.switchingCameras = YES;
                       [self reconfigureCaptureSessionInput];
                       [self updateOrientation];
                       [_captureSession startRunning];
                       [self updateDeviceCaptureFormat:format fps:fps];
                       [_currentDevice unlockForConfiguration];
-                      _isRunning = true;
+                      self.switchingCameras = NO;
+                      _isRunning = YES;
                     }];
 }
 
 - (void)stopCapture {
-  _willBeRunning = false;
+  _willBeRunning = NO;
   [RTCDispatcher
       dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
                     block:^{
@@ -160,7 +169,7 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
 #if TARGET_OS_IPHONE
                       [[UIDevice currentDevice] endGeneratingDeviceOrientationNotifications];
 #endif
-                      _isRunning = false;
+                      _isRunning = NO;
                     }];
 }
 
@@ -192,11 +201,68 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
     return;
   }
 
+#if TARGET_OS_IPHONE
+  // Default to portrait orientation on iPhone.
+  RTCVideoRotation rotation = RTCVideoRotation_90;
+  // Check here, which camera this frame is from, to avoid any race conditions.
+  AVCaptureDeviceInput *deviceInput =
+      (AVCaptureDeviceInput *)((AVCaptureInputPort *)connection.inputPorts.firstObject).input;
+  BOOL usingFrontCamera = deviceInput.device.position == AVCaptureDevicePositionFront;
+  if (self.switchingCameras) {
+    // Check the image's EXIF for the actual camera the image came from only when switching
+    // cameras as the image may still be from the old camera.
+    CFDictionaryRef attachments = CMCopyDictionaryOfAttachments(
+        kCFAllocatorDefault, sampleBuffer, kCMAttachmentMode_ShouldPropagate);
+    if (attachments) {
+      int size = CFDictionaryGetCount(attachments);
+      if (size > 0) {
+        CFDictionaryRef cfExifDictVal = NULL;
+        if (CFDictionaryGetValueIfPresent(
+                attachments, (const void *)CFSTR("{Exif}"), (const void **)&cfExifDictVal)) {
+          CFStringRef cfLensModelStrVal;
+          if (CFDictionaryGetValueIfPresent(cfExifDictVal,
+                                            (const void *)CFSTR("LensModel"),
+                                            (const void **)&cfLensModelStrVal)) {
+            if ([(__bridge NSString *)cfLensModelStrVal containsString:@"front"]) {
+              usingFrontCamera = YES;
+            } else if ([(__bridge NSString *)cfLensModelStrVal containsString:@"back"]) {
+              usingFrontCamera = NO;
+            }
+          }
+        }
+      }
+      CFRelease(attachments);
+    }
+  }
+  switch (_orientation) {
+    case UIDeviceOrientationPortrait:
+      rotation = RTCVideoRotation_90;
+      break;
+    case UIDeviceOrientationPortraitUpsideDown:
+      rotation = RTCVideoRotation_270;
+      break;
+    case UIDeviceOrientationLandscapeLeft:
+      rotation = usingFrontCamera ? RTCVideoRotation_180 : RTCVideoRotation_0;
+      break;
+    case UIDeviceOrientationLandscapeRight:
+      rotation = usingFrontCamera ? RTCVideoRotation_0 : RTCVideoRotation_180;
+      break;
+    case UIDeviceOrientationFaceUp:
+    case UIDeviceOrientationFaceDown:
+    case UIDeviceOrientationUnknown:
+      // Ignore.
+      break;
+  }
+#else
+  // No rotation on Mac.
+  RTCVideoRotation rotation = RTCVideoRotation_0;
+#endif
+
   RTCCVPixelBuffer *rtcPixelBuffer = [[RTCCVPixelBuffer alloc] initWithPixelBuffer:pixelBuffer];
   int64_t timeStampNs = CMTimeGetSeconds(CMSampleBufferGetPresentationTimeStamp(sampleBuffer)) *
-                        kNanosecondsPerSecond;
+      kNanosecondsPerSecond;
   RTCVideoFrame *videoFrame = [[RTCVideoFrame alloc] initWithBuffer:rtcPixelBuffer
-                                                           rotation:_rotation
+                                                           rotation:rotation
                                                         timeStampNs:timeStampNs];
   [self.delegate capturer:self didCaptureVideoFrame:videoFrame];
 }
@@ -399,26 +465,7 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
   NSAssert([RTCDispatcher isOnQueueForType:RTCDispatcherTypeCaptureSession],
            @"updateOrientation must be called on the capture queue.");
 #if TARGET_OS_IPHONE
-  BOOL usingFrontCamera = _currentDevice.position == AVCaptureDevicePositionFront;
-  switch ([UIDevice currentDevice].orientation) {
-    case UIDeviceOrientationPortrait:
-      _rotation = RTCVideoRotation_90;
-      break;
-    case UIDeviceOrientationPortraitUpsideDown:
-      _rotation = RTCVideoRotation_270;
-      break;
-    case UIDeviceOrientationLandscapeLeft:
-      _rotation = usingFrontCamera ? RTCVideoRotation_180 : RTCVideoRotation_0;
-      break;
-    case UIDeviceOrientationLandscapeRight:
-      _rotation = usingFrontCamera ? RTCVideoRotation_0 : RTCVideoRotation_180;
-      break;
-    case UIDeviceOrientationFaceUp:
-    case UIDeviceOrientationFaceDown:
-    case UIDeviceOrientationUnknown:
-      // Ignore.
-      break;
-  }
+  _orientation = [UIDevice currentDevice].orientation;
 #endif
 }