iPhone 13 Pro / swift / AVFoundation builtInTripleCamera : how to enable automatic switching between cameras?

Question

I am currently making a custom camera app for iOS with swiftUI AVFoundation. I also just bought iPhone 13 Pro. On the native Camera App, cameras automatically switch depending on FOCUS (ultrawide for macro / wideangle for intermediate distance / telephoto when focusing on far objects). This is also mentioned in documentation:

The built-in triple camera supports the following features: Automatic switching from one camera to another when zoom factor, light level, and focus position allow.

How can I make this work in my custom app? This is how I am selecting the camera (virtual device):

let session = AVCaptureDevice.DiscoverySession(deviceTypes: [ .builtInTripleCamera ], mediaType: AVMediaType.video, position: .unspecified)
let cameras = (session.devices.compactMap { $0 })
for camera in cameras {
  if camera.position == .back {
    self.rearCamera = camera
    try camera.lockForConfiguration()
    camera.exposureMode = .continuousAutoExposure
    camera.focusMode = .continuousAutoFocus
    camera.unlockForConfiguration()
  }
}

Is there a configuration I am missing?

Answer 1

Once you start zooming in, either by directly setting the videoZoomFactor or by calling the ramp(toVideoZoomFactor:withRate:) method for the input device, it automatically switches between the Ultrawide, Wide-angle and Telephoto lens. The switch happens based on the zoom factor being set.

A zoom factor of 1 is always the minimum. In case of the 13 Pro, setting a zoom factor of 1 will switch to the Ultrawide lens. To know which are the other zoom factors at which the system decides to switch over to the next lens, you can take a look at the virtualDeviceSwitchOverVideoZoomFactors property of the capture device. In case of the 13 Pro, it is 2 and 6 . At 2 , it will switch over to the Wide-angle lens. At 6 , it will switch over to the Telephoto lens.

You need not set any other configuration for this to work out, as long as you are using the .builtInTripleCamera device type.