EXC_BAD_ACCESS on `await session.process(inputImage:)`

[marek-ch]

Hi!
I am trying to integrate BlinkID (v 7.6.0) on iOS (Swift 6, deployment target iOS 15).

We have custom UI, so I am trying to process the image using session.process function.
However if I create it from CMSampleBuffer, I am getting EXC_BAD_ACCESS (code=1, address=0x0) errors.

Here is code that reproduces the crash:

Task {
            let inputImage = InputImage(cameraFrame: CameraFrame(buffer: MBSampleBufferWrapper(cmSampleBuffer: buffer)))
            let result = await session.process(inputImage: inputImage)
            if result.processResult?.resultCompleteness.scanningStatus == .documentScanned {
                let finalResult = await session.getResult()
                print(finalResult)
            }       
        }

Crash happens on session.process call.
If I use uiImage instead, the processing goes ok, but for performance reasons and efficient memory management, I would prefer to use CMSampleBuffer approach.

My guess would be, that somewhere in implementation of MBSampleBufferWrapper might be some concurrency related bug. It looks like system is releasing the instance of cmSampleBuffer underneath (at the end of captureOutput function).

Here is my code that takes the cmSampleBuffer output:

// MARK: - AVCaptureVideoDataOutputSampleBufferDelegate
    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
        Task {
            let result = await verifier.verifyBuffer(sampleBuffer)
            print(result)
        }
    }

where verifyBuffer calls the first snippet.

Thanks for helping me out in advance ;)

[marek-ch]

As additional info for the task.

Working solution is using ImageInput that is constructed from UIImage.

let cgImage: CGImage = newCGImage(from: buffer)! // in newCGImage function I create new CGImage from provided buffer
let inputImage = InputImage(uiImage: UIImage(cgImage: cgImage))
let result = await session.process(inputImage: inputImage)
print("\(result)")
    if result.processResult?.resultCompleteness.scanningStatus == .documentScanned {
        let finalResult = await session.getResult()
            print(finalResult)
        }
    }

Failing case is constructing ImageInput using buffer wrapper.

let inputImage = InputImage(
    cameraFrame: CameraFrame(
        buffer: MBSampleBufferWrapper(cmSampleBuffer: buffer)
    )
)

let result = await session.process(inputImage: inputImage)
print("\(result)")
    if result.processResult?.resultCompleteness.scanningStatus == .documentScanned {
        let finalResult = await session.getResult()
            print(finalResult)
        }
    }

At the time of crash the buffer object is still valid.
po buffer

CMSampleBuffer 0x107bb5640 retainCount: 7 allocator: 0x1f941c0d8
	invalid = NO
	dataReady = YES
	buffer-level attachments:
		Orientation(P) = 1
		DPIWidth  (P) = 72
		{Exif}    (P) = {
    ApertureValue = "1.356143810225275";
    BrightnessValue = "7.057297001996779";
    ColorSpace = 1;
    DateTimeDigitized = "2025:11:06 12:28:40";
    DateTimeOriginal = "2025:11:06 12:28:40";
    ExifVersion = 0232;
    ExposureBiasValue = 0;
    ExposureTime = "0.002136752136752137";
    FNumber = "1.6";
    Flash = 0;
    FocalLenIn35mmFilm = 27;
    FocalLength = "5.1";
    ISOSpeedRatings =     (
        50
    );
    LensMake = Apple;
    LensModel = "iPhone 13 mini back camera 5.1mm f/1.6";
    LensSpecification =     (
        "5.1",
        "5.1",
        "1.6",
        "1.6"
    );
    MeteringMode = 5;
    OffsetTime = "+01:00";
    OffsetTimeDigitized = "+01:00";
    OffsetTimeOriginal = "+01:00";
    PixelXDimension = 1920;
    PixelYDimension = 1080;
    SceneType = 1;
    SensingMethod = 2;
    ShutterSpeedValue = "8.870197376664363";
    SubsecTimeDigitized = 607;
    SubsecTimeOriginal = 607;
    WhiteBalance = 0;
}
		{TIFF}    (P) = {
    DateTime = "2025:11:06 12:28:40";
    HostComputer = "iPhone 13 mini";
    Make = Apple;
    Model = "iPhone 13 mini";
    ResolutionUnit = 2;
    Software = "26.1";
    XResolution = 72;
    YResolution = 72;
}
		DPIHeight (P) = 72
		{MakerApple}(P) = {
    1 = 3;
    10 = 0;
    12 =     (
        "0.1289062",
        "0.08203125"
    );
    13 = 11;
    14 = 0;
    15 = 3;
    16 = 1;
    2 = {length = 512, bytes = 0x42008000 9200a200 b000ba00 c000be00 ... cf00c600 8c00b500 };
    3 =     {
        epoch = 0;
        flags = 1;
        timescale = 1000000000;
        value = 70320615769666;
    };
    4 = 1;
    5 = 195;
    6 = 204;
    7 = 1;
    74 = 2;
    8 =     (
        "0.3679137",
        "-0.6272014",
        "-0.7173114"
    );
    9 = 0;
}
	formatDescription = <CMVideoFormatDescription 0x10862c190 [0x1f941c0d8]> {
	mediaType:'vide' 
	mediaSubType:'BGRA' 
	mediaSpecific: {
	} 
	extensions: {{
    CVBytesPerRow = 7680;
    CVImageBufferColorPrimaries = "ITU_R_709_2";
    CVImageBufferTransferFunction = "ITU_R_709_2";
    CVImageBufferYCbCrMatrix = "ITU_R_601_4";
    Version = 2;
}}
}
	numSamples = 1
	outputPTS = {70320615769666/1000000000 = 70320.616}(based on outputPresentationTimeStamp)
	sampleTimingArray[1] = {
		{PTS = {70320615769666/1000000000 = 70320.616}, DTS = {INVALID}, duration = {INVALID}},
	}
	imageBuffer = 0x1091145c0

[marek-ch]

While experimenting with the code and settings, I came across a video output configuration in our codebase:

let output = AVCaptureVideoDataOutput()
output.videoSettings = [kCVPixelBufferPixelFormatTypeKey: kCVPixelFormatType_32BGRA] as [String: Any]

When I didn’t set the kCVPixelBufferPixelFormatTypeKey, everything started working with the buffer as well.

So, at this point, there’s no need to fix anything, but it would be good to document the pixel buffer format type expected by BlinkID to avoid similar reports in the future.

Thank you :)

[PatrikKap]

Hello,

Thank you for the detailed report regarding the issue you encountered.

We recommend not processing frames directly, as doing so involves certain Swift-related issues that we had to address in a specific way.

We provide a sample app with a custom UI implementation, which we suggest reviewing. It allows you to implement a custom interface without needing to modify the underlying camera logic.

Kind regards,
Patrik