Deleting a QCamera instance and then returning to the event loop causes a read access violation due to the deferred delete of DirectShowSampleGrabber. The QCamera destructor leads to the immediate release of DSServicePlugin and hence a call to CoUninitialize, however DirectShowSampleGrabber contains a COM pointer that it still thinks is valid, and tries to use in the deferred delete, leading to the read access violation.

Min repro:

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    // make sure you have at least one camera on the system
    QCamera *camera = new QCamera(QCameraInfo::defaultCamera());
    camera->setCaptureMode(QCamera::CaptureStillImage);
    camera->start();
    QTimer::singleShot(0, [&] { delete camera; });
    return app.exec();
}

Violation is raised at line 148 of qtmultimedia/src/plugins/directshow/common/directshowsamplegrabber.cpp once control returns to the event loop after the deletion of the QCamera instance.

The deferred delete event is set up at line 440 of qtmultimedia/src/plugins/directshow/camera/dscamerasession.cpp

Not sure what the best fix would be, perhaps DirectShowSampleGrabber should call addRefCount() and releaseRefCount() from dsserviceplugin.cpp to ensure the plugin lifetime outasts its own lifetime.