I am seeking to leverage the device camera as a light sensor as described in this post. Unfortunately, the captureObject function is never called by the AVCaptureVideoDataOutputSampleBufferDelegate. It may be relevant that I am attempting this inside of a SwiftUI app, I have not seen this problem posted about or resolved in the context of a SwiftUI app.
class VideoStream: NSObject, ObservableObject,
AVCaptureVideoDataOutputSampleBufferDelegate {
@Published var luminosityReading : Double = 0.0
var session : AVCaptureSession!
override init() {
super.init()
authorizeCapture()
}
func authorizeCapture() {
// request camera permissions and call beginCapture()
...
}
func beginCapture() {
print("beginCapture entered") // prints
session = AVCaptureSession()
session.beginConfiguration()
let videoDevice = bestDevice() // func def omitted for readability
print("Device: \(videoDevice)") // prints a valid device
guard
let videoDeviceInput = try? AVCaptureDeviceInput(device: videoDevice),
session.canAddInput(videoDeviceInput)
else {
print("Camera selection failed")
return
}
let videoOutput = AVCaptureVideoDataOutput()
guard
session.canAddOutput(videoOutput)
else {
print("Error creating video output")
return
}
videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label:
"VideoQueue"))
session.addOutput(videoOutput)
session.sessionPreset = .medium
session.commitConfiguration()
session.startRunning()
}
// From: https://stackoverflow.com/questions/41921326/how-to-get-light-value-from-
avfoundation/46842115#46842115
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer,
from connection: AVCaptureConnection) {
print("captureOutput entered") // never printed
// Retrieving EXIF data of camara frame buffer
let rawMetadata = CMCopyDictionaryOfAttachments(allocator: nil, target: sampleBuffer, attachmentMode: CMAttachmentMode(kCMAttachmentMode_ShouldPropagate))
let metadata = CFDictionaryCreateMutableCopy(nil, 0, rawMetadata) as NSMutableDictionary
let exifData = metadata.value(forKey: "{Exif}") as? NSMutableDictionary
let FNumber : Double = exifData?["FNumber"] as! Double
let ExposureTime : Double = exifData?["ExposureTime"] as! Double
let ISOSpeedRatingsArray = exifData!["ISOSpeedRatings"] as? NSArray
let ISOSpeedRatings : Double = ISOSpeedRatingsArray![0] as! Double
let CalibrationConstant : Double = 50
//Calculating the luminosity
let luminosity : Double = (CalibrationConstant * FNumber * FNumber ) / ( ExposureTime * ISOSpeedRatings )
luminosityReading = luminosity
}
}
Lastly, I instantiate VideoStream as a StatreObject in my ContentView and attempt to read the updated luminosityReading:
struct ContentView: View {
@StateObject var videoStream = VideoStream()
var body: some View {
Text(String(format: "%.2f Lux", videoStream.luminosityReading))
.padding()
}
}
I have read and implemented the solutions described in these similar posts:
Using AVCaptureVideoDataOutputSampleBufferDelegate without a preview window
captureOutput not being called
captureOutput not being called from delegate
captureOutput not being called by AVCaptureAudioDataOutputSampleBufferDelegate
AVCaptureVideoDataOutput captureOutput not being called
Swift - captureOutput is not being executed
Why AVCaptureVideoDataOutputSampleBufferDelegate method is not called
Why captureOutput is never called?
func captureOutput is never called
captureOutput() function is never called swift4
Minimal Reproducible Example:
import SwiftUI
import AVKit
struct ContentView: View {
@StateObject var videoStream = VideoStream()
var body: some View {
Text(String(format: "%.2f Lux", videoStream.luminosityReading))
}
}
class VideoStream: NSObject, ObservableObject, AVCaptureVideoDataOutputSampleBufferDelegate {
@Published var luminosityReading : Double = 0.0
var session : AVCaptureSession!
override init() {
super.init()
authorizeCapture()
}
func authorizeCapture() {
switch AVCaptureDevice.authorizationStatus(for: .video) {
case .authorized: // The user has previously granted access to the camera.
beginCapture()
case .notDetermined: // The user has not yet been asked for camera access.
AVCaptureDevice.requestAccess(for: .video) { granted in
if granted {
self.beginCapture()
}
}
case .denied: // The user has previously denied access.
return
case .restricted: // The user can't grant access due to restrictions.
return
}
}
func beginCapture() {
print("beginCapture entered")
let testDevice = AVCaptureDevice.default(for: .video)
print("Image Capture Device: \(testDevice)")
guard
let videoDeviceInput = try? AVCaptureDeviceInput(device: testDevice!),
session.canAddInput(videoDeviceInput)
else {
print("Camera selection failed")
return
}
let videoOutput = AVCaptureVideoDataOutput()
guard
session.canAddOutput(videoOutput)
else {
print("Error creating video output")
return
}
videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label: "VideoQueue"))
session.addOutput(videoOutput)
session.sessionPreset = .medium
session.commitConfiguration()
session.startRunning()
}
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
print("captureOutput entered") // never printed
// light meter logic to update luminosityReading
}
}
