iphone - 如何更改 AVCaptureVideoDataOutput 的视频方向

Question

这就是问题所在。我正在使用 AVCaptureVideoDataOutput 从相机获取视频帧并使用 AVAssetWriter 从中制作视频。它工作正常，但我得到的视频是颠倒的，因为我的应用程序的设备默认方向是横向左侧，而不是 AVCaptureVideoDataOutput 中默认规定的横向右侧。我试图在 AVCaptureConnection 类中更改方向，但 isVideoOrientationSupported 始终为 false，是否可以通过某种方式修复它？

这是一些代码:

 AVCaptureDeviceInput *captureInput = [AVCaptureDeviceInput 
            deviceInputWithDevice:[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo] 
            error:nil];
 /*We setupt the output*/
 AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init]; 
 captureOutput.alwaysDiscardsLateVideoFrames = YES; 
 captureOutput.minFrameDuration = CMTimeMake(1.0, 24.0); //Uncomment it to specify a minimum duration for each video frame
 [captureOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];

 // Set the video output to store frame in BGRA (It is supposed to be faster)
 NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey; 
 NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA]; 



 NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key]; 
 [captureOutput setVideoSettings:videoSettings]; 


 /*And we create a capture session*/
 self.captureSession = [[AVCaptureSession alloc] init];
 self.captureSession.sessionPreset = AVCaptureSessionPresetLow;
 /*We add input and output*/
 if ([self.captureSession canAddInput:captureInput]) 
 {
  [self.captureSession addInput:captureInput];
 }
 if ([self.captureSession canAddOutput:captureOutput]) 
 {
  [self.captureSession addOutput:captureOutput];
 }

 /*We add the preview layer*/
 self.prevLayer = [AVCaptureVideoPreviewLayer layerWithSession: self.captureSession];

 if ([self.prevLayer isOrientationSupported]) 
 {
  [self.prevLayer setOrientation:AVCaptureVideoOrientationLandscapeLeft];
 }

 self.prevLayer.frame = self.view.bounds; 

 self.prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
 [self.view.layer addSublayer: self.prevLayer];

 AVCaptureConnection *videoConnection = NULL;

 [self.captureSession beginConfiguration];

 for ( AVCaptureConnection *connection in [captureOutput connections] ) 
 {
  for ( AVCaptureInputPort *port in [connection inputPorts] ) 
  {
   if ( [[port mediaType] isEqual:AVMediaTypeVideo] ) 
   {
    videoConnection = connection;

   }
  }
 }
    if([videoConnection isVideoOrientationSupported]) // **Here it is, its always false**
     {
        [videoConnection setVideoOrientation:AVCaptureVideoOrientationLandscapeLeft];
     }

 [self.captureSession commitConfiguration];

 [self.captureSession startRunning]; 

Upd:发现在导出视频时，AVAssetExportSession 丢失了 preferredTransform 信息。

Answer 1

我遇到了同样的问题，并在 WWDC 的 AVCamDemo 周围闲逛。我不知道为什么(还)，但是如果您在创建所有输入/输出/连接后立即查询您的 videoConnection，那么 isVideoOrientationSupported 和 supportsVideoOrientation 都会返回 NO。

但是，如果您稍后查询 supportsVideoOrientation 或 isVideoOrientationSupported(例如在设置 GUI 之后)，它将返回 YES。例如，在我调用 [[self movieFileOutput] startRecordingToOutputFileURL...]

之前，我在用户单击录制按钮后立即查询它

试一试，对我有用。