AVCaptureSession barcode scan

问题

I'm currently working with AVCaptureSession and AVCaptureMetadataOutput.

It works perfectly, but I just want to know how to indicate to scan and analyze metadata objects only on a specific region of the AVCaptureVideoPreviewLayer?

回答1:

Here is a sample of code from a project I have that may help you on the right track

    // where 'self.session' is previously setup  AVCaptureSession

    // setup metadata capture
    AVCaptureMetadataOutput *metadataOutput = [[AVCaptureMetadataOutput alloc] init];
    [self.session addOutput:metadataOutput];
    [metadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    [metadataOutput setMetadataObjectTypes:@[AVMetadataObjectTypeEAN8Code, AVMetadataObjectTypeEAN13Code]];

    // setup preview layer
    AVCaptureVideoPreviewLayer *previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session];
    previewLayer.frame = self.previewView.bounds;
    previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

    // we only want the visible area of the previewLayer to accept
    // barcode input (ignore the rest)
    // we need to convert rects coordinate system
    CGRect visibleMetadataOutputRect = [previewLayer metadataOutputRectOfInterestForRect:previewLayer.bounds];
    metadataOutput.rectOfInterest = visibleMetadataOutputRect;

    // add the previewLayer as a sublayer of the displaying UIView
    [self.previewView.layer addSublayer:previewLayer];

回答2:

In iOS 9.3.2 I had "CGAffineTransformInvert: singular matrix" error when calling metadataoutputRectOfInterestForRect. I was able to make it work calling it right after startRunning method of AVCaptureSession:

captureSession.startRunning()
let visibleRect = previewLayer.metadataOutputRectOfInterestForRect(previewLayer.bounds)
captureMetadataOutput.rectOfInterest = visibleRect

来源：https://stackoverflow.com/questions/20734929/avcapturesession-barcode-scan