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

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

 /*
  *  Copyright 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 17 matching lines @@
 }
 
 @interface RTCCameraVideoCapturer ()<AVCaptureVideoDataOutputSampleBufferDelegate>
 @property(nonatomic, readonly) dispatch_queue_t frameQueue;
 @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;
+#if TARGET_OS_IPHONE
+  UIDeviceOrientation _orientation;
+#endif
 }
 
 @synthesize frameQueue = _frameQueue;
 @synthesize captureSession = _captureSession;
 
 - (instancetype)initWithDelegate:(__weak id<RTCVideoCapturerDelegate>)delegate {
   if (self = [super initWithDelegate:delegate]) {
     // Create the capture session and all relevant inputs and outputs. We need
     // to do this in init because the application may want the capture session
     // before we start the capturer for e.g. AVCapturePreviewLayer. All objects
     // created here are retained until dealloc and never recreated.
     if (![self setupCaptureSession]) {
       return nil;
     }
     NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
 #if TARGET_OS_IPHONE
+    _orientation = UIDeviceOrientationPortrait;
     [center addObserver:self
                selector:@selector(deviceOrientationDidChange:)
                    name:UIDeviceOrientationDidChangeNotification
                  object:nil];
     [center addObserver:self
                selector:@selector(handleCaptureSessionInterruption:)
                    name:AVCaptureSessionWasInterruptedNotification
                  object:_captureSession];
     [center addObserver:self
                selector:@selector(handleCaptureSessionInterruptionEnded:)
@@ skipping 41 matching lines @@
       [eligibleDeviceFormats addObject:format];
     }
   }
 
   return eligibleDeviceFormats;
 }
 
 - (void)startCaptureWithDevice:(AVCaptureDevice *)device
                         format:(AVCaptureDeviceFormat *)format
                            fps:(NSInteger)fps {
+  _isRunning = false;

[magjed_webrtc, 2017/06/30 17:50:50]

Why is this needed?

[jtt_webrtc, 2017/06/30 17:54:49]

We need to stop frames from being processed until the inputs have been switched
over.
Otherwise, we still see the upside down video artifact.

[jtt_webrtc, 2017/06/30 18:07:47]

I removed this check and the flicker came back.

The switch over now has a very momentary black frame when it switches cameras.

[magjed_webrtc, 2017/07/03 08:23:46]

Why does it flicker if we remove this? I thought it would be synchronized by the
fact that we check from what camera device each frame comes from. And why do we
need the other checks _willBeRunning, connection.enabled, and connection.active?
I don't want to sprinkle new conditions without understanding what's happening.

   _willBeRunning = true;
   [RTCDispatcher
       dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
                     block:^{
                       RTCLogInfo("startCaptureWithDevice %@ @ %zd fps", format, fps);
 
 #if TARGET_OS_IPHONE
                       [[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
 #endif
 
                       _currentDevice = device;
 
                       NSError *error = nil;
                       if (![_currentDevice lockForConfiguration:&error]) {
                         RTCLogError(
                             @"Failed to lock device %@. Error: %@", _currentDevice, error.userInfo);
+                        _isRunning = true;

[magjed_webrtc, 2017/06/30 17:50:50]

Same here, why is this change needed?

[jtt_webrtc, 2017/06/30 17:54:49]

See above. We don't want to process frames until the switch over is complete.
If there was an error, the switch didn't happen, so we continue running.

                         return;
                       }
 
                       [self reconfigureCaptureSessionInput];
                       [self updateOrientation];
                       [_captureSession startRunning];
                       [self updateDeviceCaptureFormat:format fps:fps];
                       [_currentDevice unlockForConfiguration];
                       _isRunning = true;
                     }];
@@ skipping 28 matching lines @@
                                }];
 }
 #endif
 
 #pragma mark AVCaptureVideoDataOutputSampleBufferDelegate
 
 - (void)captureOutput:(AVCaptureOutput *)captureOutput
     didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
            fromConnection:(AVCaptureConnection *)connection {
   NSParameterAssert(captureOutput == _videoDataOutput);
+  NSParameterAssert(1 == connection.inputPorts.count);
 
-  if (CMSampleBufferGetNumSamples(sampleBuffer) != 1 || !CMSampleBufferIsValid(sampleBuffer) ||
-      !CMSampleBufferDataIsReady(sampleBuffer)) {
+  if (!_isRunning || !_willBeRunning ||

[magjed_webrtc, 2017/06/30 17:50:50]

Why do we need these extra checks? What happens otherwise?

[jtt_webrtc, 2017/06/30 17:54:49]

See above, we still get the flicker but more rare.

+      CMSampleBufferGetNumSamples(sampleBuffer) != 1 ||
+      !CMSampleBufferIsValid(sampleBuffer) ||
+      !CMSampleBufferDataIsReady(sampleBuffer) || !connection.enabled ||
+      !connection.active) {
     return;
   }
 
   CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
   if (pixelBuffer == nil) {
     return;
   }
 
+#if TARGET_OS_IPHONE
+  // Default to portrait orientation on iPhone.
+  RTCVideoRotation rotation = RTCVideoRotation_90;
+  AVCaptureDeviceInput *deviceInput =
+      (AVCaptureDeviceInput *)((AVCaptureInputPort *)
+                                   connection.inputPorts.firstObject)
+          .input;
+  BOOL usingFrontCamera =
+      deviceInput.device.position == AVCaptureDevicePositionFront;
+  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;
-  RTCVideoFrame *videoFrame = [[RTCVideoFrame alloc] initWithBuffer:rtcPixelBuffer
-                                                           rotation:_rotation
-                                                        timeStampNs:timeStampNs];
+  RTCVideoFrame *videoFrame =
+      [[RTCVideoFrame alloc] initWithBuffer:rtcPixelBuffer
+                                   rotation:rotation
+                                timeStampNs:timeStampNs];
   [self.delegate capturer:self didCaptureVideoFrame:videoFrame];
 }
 
 - (void)captureOutput:(AVCaptureOutput *)captureOutput
     didDropSampleBuffer:(CMSampleBufferRef)sampleBuffer
          fromConnection:(AVCaptureConnection *)connection {
   RTCLogError(@"Dropped sample buffer.");
 }
 
 #pragma mark - AVCaptureSession notifications
@@ skipping 181 matching lines @@
   } else {
     RTCLogError(@"Cannot add camera as an input to the session.");
   }
   [_captureSession commitConfiguration];
 }
 
 - (void)updateOrientation {
   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
 }
 
 @end