test.m

    AVCaptureSession *session = [[AVCaptureSession alloc] init];
    AVCaptureDevice *camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:camera error:nil];
    [session addInput:input];
    AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];

    CGRect region = CGRectMake (self.view.bounds.origin.x + 10, self.view.bounds.size.height / 2 - 35, self.view.bounds.size.width - 20, 70);
    
    [session addOutput:output];
    
    AVCaptureVideoPreviewLayer *previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
    previewLayer.masksToBounds = YES;
    previewLayer.videoGravity = AVLayerVideoGravityResize;
    previewLayer.frame = [[UIScreen mainScreen] bounds];
    
    CGRect reg = [output metadataOutputRectOfInterestForRect: region];
    NSLog (@"region: %f %f %f %f", region.origin.x, region.origin.y, region.size.width, region.size.height);
    NSLog (@"reg:    %f %f %f %f", reg.origin.x, reg.origin.y, reg.size.width, reg.size.height);

region: 10.000000 349.000000 1004.000000 70.000000
reg: 10.000000 349.000000 1004.000000 70.000000