[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..0b58297a0fbbba9751eae8c5ca5a3377c325e1fd 100644
--- a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m
+++ b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m
@@ -19,6 +19,7 @@
 #endif
 
 #import "RTCDispatcher+Private.h"
+#import "RTCImageHelper.h"
 
 const int64_t kNanosecondsPerSecond = 1000000000;
 
@@ -35,11 +36,13 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
   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;
+#if TARGET_OS_IPHONE
+  UIDeviceOrientation _orientation;
+#endif
 }
 
 @synthesize frameQueue = _frameQueue;
@@ -56,6 +59,7 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
     }
     NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
 #if TARGET_OS_IPHONE
+    _orientation = UIDeviceOrientationPortrait;
     [center addObserver:self
                selector:@selector(deviceOrientationDidChange:)
                    name:UIDeviceOrientationDidChangeNotification
@@ -117,7 +121,7 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
 - (void)startCaptureWithDevice:(AVCaptureDevice *)device
                         format:(AVCaptureDeviceFormat *)format
                            fps:(NSInteger)fps {
-  _willBeRunning = true;
+  _willBeRunning = YES;
   [RTCDispatcher
       dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
                     block:^{
@@ -141,12 +145,12 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
                       [_captureSession startRunning];
                       [self updateDeviceCaptureFormat:format fps:fps];
                       [_currentDevice unlockForConfiguration];
-                      _isRunning = true;
+                      _isRunning = YES;
                     }];
 }
 
 - (void)stopCapture {
-  _willBeRunning = false;
+  _willBeRunning = NO;
   [RTCDispatcher
       dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
                     block:^{
@@ -160,7 +164,7 @@ static inline BOOL IsMediaSubTypeSupported(FourCharCode mediaSubType) {
 #if TARGET_OS_IPHONE
                       [[UIDevice currentDevice] endGeneratingDeviceOrientationNotifications];
 #endif
-                      _isRunning = false;
+                      _isRunning = NO;
                     }];
 }
 
@@ -192,11 +196,48 @@ 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;
+  // Check the image's EXIF for the actual camera the image came as the image could have been
+  // delayed as we set alwaysDiscardsLateVideoFrames to NO.
+  AVCaptureDevicePosition cameraPosition = [RTCImageHelper cameraFromSampleBuffer:sampleBuffer];

[tkchin_webrtc, 2017/07/24 21:30:37]

nit: name the method more appropriately for the return type. The method isn't
returning a camera from a sample buffer.
devicePositionForSampleBuffer?

[jtt_webrtc, 2017/07/24 22:29:51]

Done.

+  if (cameraPosition != AVCaptureDevicePositionUnspecified) {
+    usingFrontCamera = cameraPosition == AVCaptureDevicePositionFront;
+  }
+  switch (_orientation) {

[tkchin_webrtc, 2017/07/24 21:30:37]

orientation is set from the capture session queue, but you are accessing it on
the frame queue. Will this cause problems?

This is old behavior anyway, so I won't block CL. But would be good to
understand / fix later.

[jtt_webrtc, 2017/07/24 22:29:51]

Acknowledged.

+    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 +440,7 @@ 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
 }