How do you use setRectOfInterest for AVCaptureSession

Question

I'm struggling with how to impliment AVCaptureSession 's setRectOfInterest method.
To make things simple... there's some sample code in the WWDC sample code (2013) called QRchestra.
Right now the scanning of barcodes is for the entire preview area... but lets say I want to limit it to half the screen.
The ReceiveViewController gets the meta data from SessionManager.
Now in RecieveViewController viewDidLoad I can do :
self.sessionManager = [[SessionManager alloc] init];
[self.sessionManager startRunning];
AVCaptureVideoPreviewLayer *previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.sessionManager.captureSession];
CGRect metadataRect = [previewLayer metadataOutputRectOfInterestForRect:CGRectMake(160, 0, 320, 348)];
That should give me the coordinates translated for the frame of refference of the preview screen.
According to WWDC I would apply that to the metadata output :
[metadataOutput setRectOfInterest:metadataRect];
That sould be it - but the issue I am having is finding that metadataOutput object.
It exists in SessionManager but must be private or something as it doesn't appear to be exposed to ReceiveView Controller vis self.SessionManager.
Google has been of no help with setRectOfInterest so I'm coming to you fine people.
Anyone able to shed some light on this for me?

Answer 1

Not really my bag, this, but did you look at the class reference for AVMetadataObject? apparently you never create a metadata object directly but get one by using an AVCaptureMetadataOutput object. As best I can grok this on brief (totally underinformed) inspection, you start with a capture session then use the addOutput method to add an appropriate metadata object. The rectOfInterest property is set on that rather than on the session itself.
If that doesn't help, sorry!