同一个 AVCaptureSession 中的多个 AVCaptureVideoDataOutput

Question

我想知道是否可以通过单个相机设备输入将多个 AVCaptureVideoDataOutput 添加到 AVCaptureSession？

我的实验表明，添加第二个 VideoDataOutput 会导致 canAddOutput return NO。但是我在 Apple 的文档中找不到任何地方说不允许多数据输出。

Answer 1

我们不能对多个 AVCaptureVideoDataOutput 对象使用单个 AVCaptureSession。

你能做的是用多个 AVCaptureSession 对象制作多个 AVCaptureVideoDataOutput。

您可以创建AVCaptureVideoDataOutput和AVCaptureSession两个不同的设置，然后您可以在应用程序中一个接一个地使用它们，您将能够实现目标。

在我的例子中，我必须同时使用相机拍摄正面和背面图像。

我确实为 AVCaptureVideoDataOutput 和 AVCaptureSession 创建了两个不同的对象，如下所示。

/* Front camera settings */
@property bool isFrontRecording;
@property (strong, nonatomic) AVCaptureDeviceInput *videoInputBack;
@property (strong, nonatomic) AVCaptureStillImageOutput *imageOutputBack;
@property (strong, nonatomic) AVCaptureSession *sessionBack;

/* Back camera settings */
@property bool isBackRecording;
@property (strong, nonatomic) AVCaptureDeviceInput *videoInputFront;
@property (strong, nonatomic) AVCaptureStillImageOutput *imageOutputFront;
@property (strong, nonatomic) AVCaptureSession *sessionFront;

现在在视图中最初加载我设置了后置摄像头并设置了会话开始记录或不开始记录的标志，如下所示。

- (void)viewDidLoad {
    [super viewDidLoad];

    [self setupBackAVCapture];

    self.isFrontRecording = NO;
    self.isBackRecording = NO;
}

- (void)setupBackAVCapture
{
    NSError *error = nil;

    self.sessionBack = [[AVCaptureSession alloc] init];
    self.sessionBack.sessionPreset = AVCaptureSessionPresetPhoto;

    AVCaptureDevice *camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    self.videoInputBack = [[AVCaptureDeviceInput alloc] initWithDevice:camera error:&error];
    [self.sessionBack addInput:self.videoInputBack];

    self.imageOutputBack = [[AVCaptureStillImageOutput alloc] init];
    [self.sessionBack addOutput:self.imageOutputBack];

}

现在，每当用户开始拍摄照片时，我们都会使用以下代码拍摄正面照片。

- (IBAction)buttonCapture:(id)sender {
    [self takeBackPhoto];
}

- (void)takeBackPhoto
{
    [self.sessionBack startRunning];
    if (!self.isFrontRecording) {

        self.isFrontRecording = YES;

        AudioServicesPlaySystemSound(kSystemSoundID_Vibrate);
        AVCaptureConnection *videoConnection = [self.imageOutputBack connectionWithMediaType:AVMediaTypeVideo];

        if (videoConnection == nil) {
            return;
        }


        [self.imageOutputBack
         captureStillImageAsynchronouslyFromConnection:videoConnection
         completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {

             if (imageDataSampleBuffer == NULL) {
                 return;
             }

             NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];

             UIImage *image = [[UIImage alloc] initWithData:imageData];

             UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);

             [self.imageView setImage:image];

             [self.sessionBack stopRunning];

             // Set up front camera setting and capture photo.
             [self setupFrontAVCapture];
             [self takeFrontPhoto];

         }];

        self.isFrontRecording = NO;

    }

}

一旦捕获背面图像，我们将设置会话以使用 setupFrontAVCapture 方法捕获正面图像，然后我们将使用 takeFrontPhoto[ 捕获正面图像=46=] 方法如下。

- (void)setupFrontAVCapture { NSError *error = nil; self.sessionFront = [[AVCaptureSession alloc] init]; self.sessionFront.sessionPreset = AVCaptureSessionPresetPhoto; AVCaptureDevice *camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; camera = [self cameraWithPosition:AVCaptureDevicePositionFront]; self.videoInputFront = [[AVCaptureDeviceInput alloc] initWithDevice:camera error:&error]; [self.sessionFront addInput:self.videoInputFront]; self.imageOutputFront = [[AVCaptureStillImageOutput alloc] init]; [self.sessionFront addOutput:self.imageOutputFront]; } - (void)takeFrontPhoto { [self.sessionFront startRunning]; if (!self.isBackRecording) { self.isBackRecording = YES; AudioServicesPlaySystemSound(kSystemSoundID_Vibrate); AVCaptureConnection *videoConnection = [self.imageOutputFront connectionWithMediaType:AVMediaTypeVideo]; if (videoConnection == nil) { return; } [self.imageOutputFront captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) { if (imageDataSampleBuffer == NULL) { return; } NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer]; UIImage *image = [[UIImage alloc] initWithData:imageData]; UIImageWriteToSavedPhotosAlbum(image, self, nil, nil); [self.imageViewBack setImage:image]; [self.sessionFront stopRunning]; }]; self.isBackRecording = NO; } }

这样您就可以使用两组不同的 AVCaptureSession 和 AVCaptureStillImageOutput 对象来实现您的目标。

如果您有任何困惑，请告诉我。

同一个 AVCaptureSession 中的多个 AVCaptureVideoDataOutput

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