Device torch turns off when starting AVCaptureSession - ios

Question

I'm using AVCaptureSession to capture video.
I want to light on the torch during the whole session, but once the session is started, the light turns automatically off.
There is a lot of posts here showing how to turn on the torch. It works, unless the capture session is started.
here's the way I start the session
guard let camera = AVCaptureDevice.default(for: .video) else { return }
self.captureSession.beginConfiguration()
let deviceInput = try AVCaptureDeviceInput(device: camera)
self.captureSession.addInput(deviceInput)
let videoOutput = AVCaptureVideoDataOutput()
videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label: "com.axelife.axcapturer.samplebufferdelegate"))
self.captureSession.addOutput(videoOutput)
try camera.setLight(on: true)
self.captureSession.commitConfiguration()
DispatchQueue(label: "capturesession").async {
self.captureSession.startRunning()
}
And my code to turn on the light
extension AVCaptureDevice {
func setLight(on: Bool) throws {
try self.lockForConfiguration()
if on {
try self.setTorchModeOn(level: 1)
}
else {
self.torchMode = .off
}
self.unlockForConfiguration()
}
}
With that code, the light turns on during < 0.5 seconds, and turn back off automatically.

Answer 1

Ok, I figured out.
The torch simply must be lighted on after the session start.
So instead of:
try camera.setLight(on: true)
self.captureSession.commitConfiguration()
DispatchQueue(label: "capturesession").async {
self.captureSession.startRunning()
}
just do
self.captureSession.commitConfiguration()
DispatchQueue(label: "capturesession").async {
self.captureSession.startRunning()
try camera.setLight(on: true)
}

Answer 2

For me, the torch turns off when I change the videoOrientation of the capture preview layer. I turn it on again after that happens. (DispatchQueue.main.async is important, for some reason, it doesn't work if I leave it out)
previewConnection.videoOrientation = orientation
do {
try captureDevice.lockForConfiguration()
} catch {
print(error)
}
DispatchQueue.main.async { [weak self] in
self?.captureDevice.torchMode = .on
self?.captureDevice.unlockForConfiguration()
}