Unity Vuforia Extension EXC_BAD_ACCESS with AVCaptureSession

Question

So I am using Unity 2017.2.0f3 with the Vuforia Extension, and I imported the project in an extant iOS project following the https://github.com/blitzagency/ios-unity5 tutorial. The extant iOS project included a view in which you can toggle between an AR view which uses Vuforia, and a native iOS AVCaptureSession which can scan barcodes. The former works without error, but as soon as I try to do

session.addInput

or

session.addOutput

the latter feature crashes with:

EXC_BAD_ACCESS

within the

com.apple.avfoundation.videodataoutput.bufferqueue

Queue.
I tried to use NSZombie to learn more about what kind of object was trying to be sent a message, but i can only run the application on a physical device, and thus I can't learn more about the actual object it tries to send a message to which causes the crash.

My reasoning is that it may have to do with Vuforia persisting a reference to a freed VIdeoDataOutput Buffer Queue which is triggered by my creation of a new

AVCaptureSession

with an

AVCaptureOutput

and an

AVCaptureInput

. What is tricky is that I don't know how to actually ascertain this or not since it is a third party library. The only ViewController which has an Objective-C wrapper is called

CameraCapture.mm

but this seems to be a vestigial Unity only View Controller, since any

NSLogs

or breakpoints I put in that method are not called.

private func setupCamera() {

    guard let device = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo),

        let input = try? AVCaptureDeviceInput(device: device) else {

            return

    }



    if session.canAddInput(input) {

        session.addInputWithNoConnections(input)

    }



    previewLayer = AVCaptureVideoPreviewLayer(session: session)

    previewLayer.frame = self.view.bounds

    previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill

    view.layer.addSublayer(previewLayer)

    cameraPreviewView.layer.addSublayer(previewLayer)

    let metadataOutput = AVCaptureMetadataOutput()



    if session.canAddOutput(metadataOutput) {

        session.addOutputWithNoConnections(metadataOutput)



        metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)

        metadataOutput.metadataObjectTypes = metadataOutput.availableMetadataObjectTypes

    } else {

        print("Could not add metadata output")

    }

}

Once the above method is called, even after calling the

AppDelegate

function from the blitz tutorial

appDelegate.stopUnity()

always crashes the app.

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Answer 1

So basically the error I was getting was from Unity not truly exiting when in background. This is a setting which is configurable for iOS Unity exports in Unity itself. If you go to Edit> Player Settings> and then in the Inspector on the right under Other Settings there is a field called Behavior In Background. My original export had this set to Suspend and this caused the AVCaptureSession intrinsic to a Camera in Unity/Vuforia to not be probably cleaned up, in terms of its videoOutput delegate buffer, when Unity wasn't running, thus the resulting EXC_BAD_ACCESS when thinking I had Unity stopped and starting a new AVCaptureSession. So by switching Behavior In Background to Exit and then guaranteeing in my app that I had called appDelegate.stopUnity() before doing setting up input/output pairs for a new AVCaptureSession() successfully fixed the issue.

Unity Vuforia Extension EXC_BAD_ACCESS with AVCaptureSession

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