AVFoundation Switching Cameras Slow (Connected To Sample Buffer) - ios

Question

override func viewDidLoad() {
super.viewDidLoad()
...
setupDevice()
setupInputOutput()
}
View did load starts the setup chain
func setupDevice() {
let deviceDiscoverySession = AVCaptureDevice.DiscoverySession(deviceTypes: [AVCaptureDevice.DeviceType.builtInWideAngleCamera], mediaType: AVMediaType.video, position: AVCaptureDevice.Position.unspecified)
let devices = deviceDiscoverySession.devices
for device in devices {
if device.position == AVCaptureDevice.Position.back {
backCamera = device
setupCorrectFramerate(currentCamera: backCamera!)
}
else if device.position == AVCaptureDevice.Position.front {
frontCamera = device
setupCorrectFramerate(currentCamera: frontCamera!)
}
}
currentCamera = cameraModeIsBack ? backCamera : frontCamera
}
var deviceInput: AVCaptureDeviceInput?
let videoOutput = AVCaptureVideoDataOutput()
func setupInputOutput() {
do {
let captureDeviceInput = try AVCaptureDeviceInput(device: currentCamera!)
deviceInput = captureDeviceInput
captureSession.sessionPreset = AVCaptureSession.Preset.hd1280x720
if captureSession.canAddInput(deviceInput!) {
captureSession.addInput(deviceInput!)
}
videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label: "sample buffer delegate", attributes: []))
if captureSession.canAddOutput(videoOutput) {
captureSession.addOutput(videoOutput)
}
captureSession.startRunning()
if(firstTime){
setupMetal()
}
firstTime = false
toggleCamerButton.isEnabled = true
} catch {
print(error)
}
}
On a high level I find the device inputs, setup their framerate and setup the capture session, (the buffer output gets processed to a MTKView).
The issue is when I change cameras. It's either snappy and isntant or becomes very slow and freezes for 4-5 seconds before responding.
The logic I use to change the cameras:
func updateCameras(){
DispatchQueue.global().async {
self.captureSession.stopRunning()
self.captureSession.removeInput(self.deviceInput!)
self.currentCamera = self.cameraModeIsBack ? self.backCamera : self.frontCamera
self.changeCameras()
}
}
func changeCameras(){
do {
let captureDeviceInput = try AVCaptureDeviceInput(device: self.currentCamera!)
self.deviceInput = captureDeviceInput
if self.captureSession.canAddInput(self.deviceInput!) {
self.captureSession.addInput(self.deviceInput!)
}
self.captureSession.startRunning()
DispatchQueue.main.async {
self.toggleCamerButton.isEnabled = true
}
} catch {
print(error)
}
}
I've revised it as much as I can. Switching cameras is essentially
Stopping the camera session
removing the input
adding the input
starting the session
I have no idea why on earth it's so variable (works perfectly most of the time on my iPhone X while on my iPhone 6 it's always slow).

Answer 1

I suspect the calls to manipulate the cameraSession should be done on the main thread. Try changing updateCameras() to use DispatchQueue.main.async() instead of DispatchQueue.global().async
Like this:
func updateCameras(){
DispatchQueue.main.async {
self.captureSession.stopRunning()
self.captureSession.removeInput(self.deviceInput!)
self.currentCamera = self.cameraModeIsBack ? self.backCamera : self.frontCamera
self.changeCameras()
}
}
With that change the call to DispatchQueue.main.async() in your changeCameras() function should no longer be needed