同一个 AVCaptureSession 中的多个 AVCaptureVideoDataOutput

Question

我想知道是否可以使用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将导致canAddOutput返回NO 。 但是我在 Apple 的文档中找不到任何地方说不允许输出多个数据。

Answer 1

我们不能将单个AVCaptureSession用于多个AVCaptureVideoDataOutput对象。

你能做的是你可以用多个AVCaptureSession对象制作多个AVCaptureVideoDataOutput 。

您可以创建AVCaptureVideoDataOutput和AVCaptureSession两种不同设置，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。

就我而言，我必须一次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;

现在视图确实加载了最初我确实设置了后置摄像头并为会话设置了标志，如下所示是否开始录制或不为两个会话。

- (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，我们将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;

    }

}

一旦捕捉到背面图像，我们将设置会话以使用setupFrontAVCapture方法捕捉正面图像，然后我们将使用takeFrontPhoto方法捕捉正面图像，如下所示。

- (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;

    }

}

这样你就可以使用两组不同的AVCaptureSession和AVCaptureStillImageOutput对象，你就可以实现你的目标。

如果您有任何困惑，请告诉我。