Realtime zoom from AVCaptureVideoPreviewLayer - ios

Question

I am implementing a camera application. I initiate the camera as follows:
let input = try AVCaptureDeviceInput(device: captureDevice!)
captureSession = AVCaptureSession()
captureSession?.addInput(input)
videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession!)
videoPreviewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
videoPreviewLayer?.frame = view.layer.bounds
previewView.layer.insertSublayer(videoPreviewLayer!, at: 0)
Now I want to have a small rectangle on top of the preview layer. In that rectangle area, I want to zoom a specific area from the preview layer. To do it, I add a new UIView on top of other views, but I don't know how to display a specific area from the previewer (e.g. zoom factor = 2).
The following figure shows what I want to have:
How can I do it?

Answer 1

Finally, I found a solution.
The idea is to extract the real-time frames from the output of the camera, then use an UIImage view to show the enlarged frame. Following is the portion of code to add an video output:
let videoOutput = AVCaptureVideoDataOutput()
videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label: "sample buffer"))
guard captureSession.canAddOutput(videoOutput) else { return }
captureSession.addOutput(videoOutput)
and we need to implement a delegate function:
func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
guard let uiImage = imageFromSampleBuffer(sampleBuffer: sampleBuffer) else { return }
DispatchQueue.main.async { [unowned self] in
self.delegate?.captured(image: uiImage)
}
}
private func imageFromSampleBuffer(sampleBuffer: CMSampleBuffer) -> UIImage? {
guard let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return nil }
let ciImage = CIImage(cvPixelBuffer: imageBuffer)
guard let cgImage = context.createCGImage(ciImage, from: ciImage.extent) else { return nil }
return UIImage(cgImage: cgImage)
}
The code was taken from this article.