Can't start iPhone X flash in touch mode - ios

Question

I have problems with running iPhone X flash in torch mode.
Back AVCaptureDeviceTypeBuiltInTelephotoCamera selected as capture device:
com.apple.avfoundation.avcapturedevice.built-in_video:2' -
AVCaptureDeviceTypeBuiltInTelephotoCamera
After checking touch mode availability with:
[self.captureDevice isTorchModeSupported:AVCaptureTorchModeOn]
I'm trying to switch flash light into torch mode with
[self.captureDevice lockForConfiguration:nil];
BOOL result = [self.captureDevice setTorchModeOnWithLevel:1 error:&error];
[self.captureDevice unlockForConfiguration];
This call is successful. result == YES and error == nil. But flash light blinks once then turns off.
I saw this behaviour on iPhone X myself and there is a reports of the same behaviour from iPhone 8 and iPhone 8 Plus owners. Some users say that this problem appeared after update to iOS 11.1. But I couldn't reproduce it with iPhone 8 myself.
Is there any ideas how to fix or debug this problem?
Full code snippet from my app listed below:
// Retrieve the back camera
if ([AVCaptureDeviceDiscoverySession class]) {
DDLogDebug(#"Search camera with AVCaptureDeviceDiscoverySession");
AVCaptureDevice* camera =
[AVCaptureDeviceDiscoverySession
discoverySessionWithDeviceTypes: #[AVCaptureDeviceTypeBuiltInTelephotoCamera]
mediaType:AVMediaTypeVideo
position:AVCaptureDevicePositionBack].devices.firstObject;
if (!camera) {
camera = [AVCaptureDeviceDiscoverySession
discoverySessionWithDeviceTypes: #[AVCaptureDeviceTypeBuiltInTelephotoCamera]
mediaType:AVMediaTypeVideo
position:AVCaptureDevicePositionBack].devices.firstObject;
}
DDLogDebug(#"Did find %# camera", camera);
self.captureDevice = camera;
} else {
DDLogDebug(#"Haven't found camera device with AVCaptureDeviceDiscoverySession");
}
if (!self.captureDevice) {
DDLogDebug(#"Searching at [AVCaptureDevice devices], where %lu devices available", (unsigned long)AVCaptureDevice.devices.count);
for (AVCaptureDevice *device in [AVCaptureDevice devices]) {
if ([device hasMediaType:AVMediaTypeVideo] && [device hasTorch]) {
self.captureDevice = device;
break;
}
}
}
if (!self.captureDevice) {
NSError* error = [NSError buildError:^(MRErrorBuilder *builder) {
builder.localizedDescription = NSLocalizedString(#"There is no camera devices able to measure heart rate", nil);
builder.domain = kWTCameraHeartRateMonitorError;
builder.code = 27172;
}];
DDLogError(#"%#", error);
self.session = nil;
self.handler(0, 0, error);
return NO;
}
NSError *error;
AVCaptureDeviceInput *input = [[AVCaptureDeviceInput alloc] initWithDevice:self.captureDevice
error:&error];
if (error) {
DDLogError(#"%#", error);
self.session = nil;
self.handler(0, 0, error);
return NO;
}
NSString* deviceType = [self.captureDevice respondsToSelector:#selector(deviceType)] ? self.captureDevice.deviceType : #"Unknown";
DDLogDebug(#"Configurating camera '%#'/'%#' - %# id %# at %ld connected: %#", self.captureDevice.localizedName, self.captureDevice.modelID, deviceType, self.captureDevice.uniqueID, (long)self.captureDevice.position, self.captureDevice.connected?#"YES":#"NO");
self.session = [[AVCaptureSession alloc] init];
NSString* preset = [self.session canSetSessionPreset:AVCaptureSessionPresetLow] ? AVCaptureSessionPresetLow : nil;
if (preset) {
self.session.sessionPreset = preset;
}
[self.session beginConfiguration];
[self.session addInput:input];
// Find the max frame rate we can get from the given device
AVCaptureDeviceFormat *currentFormat;
for (AVCaptureDeviceFormat *format in self.captureDevice.formats)
{
NSArray *ranges = format.videoSupportedFrameRateRanges;
AVFrameRateRange *frameRates = ranges[0];
// Find the lowest resolution format at the frame rate we want.
if (frameRates.maxFrameRate == FRAMES_PER_SECOND && (!currentFormat || (CMVideoFormatDescriptionGetDimensions(format.formatDescription).width < CMVideoFormatDescriptionGetDimensions(currentFormat.formatDescription).width && CMVideoFormatDescriptionGetDimensions(format.formatDescription).height < CMVideoFormatDescriptionGetDimensions(currentFormat.formatDescription).height)))
{
currentFormat = format;
}
}
if (![self.captureDevice isTorchModeSupported:AVCaptureTorchModeOn]) {
NSError* error = [NSError buildError:^(MRErrorBuilder *builder) {
builder.localizedDescription = NSLocalizedString(#"Torch mode is not supported for your camera", nil);
builder.domain = kWTCameraHeartRateMonitorError;
builder.code = 28633;
}];
self.session = nil;
DDLogError(#"%#", error);
self.session = nil;
self.handler(0, 0, error);
return NO;
}
// Tell the device to use the max frame rate.
[self.captureDevice lockForConfiguration:nil];
DDLogVerbose(#"Turn on tourch mode with level 0.5");
self.captureDevice.flashMode = AVCaptureFlashModeOff;
BOOL result = [self.captureDevice setTorchModeOnWithLevel:0.5 error:&error];
if (!result) {
DDLogError(#"%#", error);
self.session = nil;
self.handler(0, 0, error);
return NO;
}
[self.captureDevice setFocusMode:AVCaptureFocusModeLocked];
[self.captureDevice setFocusModeLockedWithLensPosition:1.0
completionHandler:nil];
self.captureDevice.activeFormat = currentFormat;
self.captureDevice.activeVideoMinFrameDuration = CMTimeMake(1, FRAMES_PER_SECOND);
self.captureDevice.activeVideoMaxFrameDuration = CMTimeMake(1, FRAMES_PER_SECOND);
[self.captureDevice unlockForConfiguration];
// Set the output
AVCaptureVideoDataOutput* videoOutput = [AVCaptureVideoDataOutput new];
// create a queue to run the capture on
dispatch_queue_t captureQueue=dispatch_queue_create("catpureQueue", DISPATCH_QUEUE_SERIAL);
// setup our delegate
[videoOutput setSampleBufferDelegate:self queue:captureQueue];
// configure the pixel format
videoOutput.videoSettings = #{(id)kCVPixelBufferPixelFormatTypeKey: #(kCVPixelFormatType_32BGRA)};
videoOutput.alwaysDiscardsLateVideoFrames = NO;
[self.session addOutput:videoOutput];
if (debugPath) {
NSError* error;
[[NSFileManager defaultManager] removeItemAtPath:debugPath
error:nil];
BOOL result =
[[NSFileManager defaultManager] createDirectoryAtPath:debugPath
withIntermediateDirectories:YES
attributes:nil
error:&error];
if (result) {
[self setupDebugRecordAt:debugPath withFormat:currentFormat];
} else {
DDLogError(#"%#", error);
}
const char* path = [debugPath cStringUsingEncoding:NSUTF8StringEncoding];
self.filter->setDebugPath(path);
}
// Start the video session
[self.session commitConfiguration];
self.frameNumber = 0;
[self.assetWriter startWriting];
[self.assetWriter startSessionAtSourceTime:kCMTimeZero];
[self.session startRunning];

Answer 1

Finally, the problem is fixed. I'm not sure about exact reason. Any information related to this issue are appreciated.
This problem exists on iPhone 8, 8+ and iPhone X running iOS 11.1. I've reproduced this behaviour on iPhone 8 after updating form iOS from 11.0 to 11.1.
What I noticed is that torch turns on after calling
BOOL result = [self.captureDevice setTorchModeOnWithLevel:0.5 error:&error];
and turns off after
[self.captureDevice setFocusMode:AVCaptureFocusModeLocked];
or
[self.session commitConfiguration];
So the solution was to perform torch configuration where ALL other session and device configurations are finished and session is started.
My current implementation is:
// Session configuration ...
[self.session startRunning];
if (![self.captureDevice isTorchModeSupported:AVCaptureTorchModeOn]) {
NSError* error = [NSError buildError:^(MRErrorBuilder *builder) {
builder.localizedDescription = NSLocalizedString(#"Torch mode is not supported for your camera", nil);
builder.domain = kWTCameraHeartRateMonitorError;
builder.code = 28633;
}];
DDLogError(#"%#", error);
if (self.session) {
[self.session stopRunning];
}
self.session = nil;
self.handler(0, 0, error);
return NO;
}
[self.captureDevice lockForConfiguration:nil];
self.captureDevice.flashMode = AVCaptureFlashModeOff;
[self.captureDevice setFocusMode:AVCaptureFocusModeLocked];
[self.captureDevice setFocusModeLockedWithLensPosition:1.0
completionHandler:nil];
self.captureDevice.activeFormat = currentFormat;
self.captureDevice.activeVideoMinFrameDuration = CMTimeMake(1, FRAMES_PER_SECOND);
self.captureDevice.activeVideoMaxFrameDuration = CMTimeMake(1, FRAMES_PER_SECOND);
// This call should be placed AFTER all other configurations
BOOL result = [self.captureDevice setTorchModeOnWithLevel:0.5 error:&error];
if (!result) {
DDLogError(#"%#", error);
self.session = nil;
self.handler(0, 0, error);
return NO;
}
[self.captureDevice unlockForConfiguration];