I'm currently writing a C++ Qt App that takes a webcam feed and applies some processing to each frame before rending the processed frame to the app. The problem I'm getting is that when I start my Qt App, whether the VideoSink receives any frames to process is wildly inconsistent -- either it works completely fine, or I don't receive a single frame for the lifetime of the app. No middle ground.

MainWindow::MainWindow(QWidget* parent)
    : QWidget(parent) {
    // Layout
    QHBoxLayout* mainLayout = new QHBoxLayout(this);

    // Video Display Widget
    m_videoStream = new QLabel(this);
    QImage blackImage(640, 480, QImage::Format_RGB888);
    blackImage.fill(QColor(Qt::black));
    m_videoStream->setPixmap(QPixmap::fromImage(blackImage));
    mainLayout->addWidget(m_videoStream);

    // Camera Setup
    m_camera = new QCamera(this);
    for (const QCameraDevice& device : QMediaDevices::videoInputs()) {
        if (device.description() == "Depstech webcam (V4L2)")
            m_camera->setCameraDevice(device);
    }
    m_imageCapture = new QImageCapture(this);

    // Create video sink to intercept video frames
    m_videoSink = new QVideoSink(this);

    // Media Session Setup
    m_captureSession.setCamera(m_camera);
    m_captureSession.setImageCapture(m_imageCapture);
    m_captureSession.setVideoOutput(m_videoSink);
    m_camera->start();

    // Make connections
    connect(m_videoSink, &QVideoSink::videoFrameChanged, this, &MainWindow::processFrame);
}

Things I noticed

Other webcam based apps on my computer such as "Cheese" do not run into this issue.

Regardless of whether I called m_camera->start();, the camera feed still appeared just as often as when I exclude it entirely from my code. Even if the camera is NOT active, I'll still be receiving frames and rendering them.

When the frames are not being received, my webcam's light doesn't even turn on.

Things I've Tried

Switching cameras back and forth does not seem to help.

Connecting another camera (HuddleCamHD [V4L2]) instead, did not help.

My brain went straight to "race-condition", but adding a few seconds delay when initializing the capture session or when connecting the VideoSink::videoFrameChanged signal, did not help.

Debug Prints