Nothing output about video streaming.

void CPreviewPage::startVideoStreaming(void)
{
    QString str_id;
    QString str_vid;
    QString str_pid;

    const QList<QCameraDevice> cameras = QMediaDevices::videoInputs();
    for (const QCameraDevice &camera_device : cameras)

    {
        example id = "0x2600000a16809b0" or "0x100000a1680970" qDebug() << "camera_device.id = " << camera_device.id();
        str_id = camera_device.id().right(8);
        str_vid = str_id.mid(0, 4);
        str_pid = str_id.right(4);
        qDebug() << "id = " << str_id;
        qDebug() << "vid = 0x" << str_vid;
        qDebug() << "pid = 0x" << str_pid;
        if (str_vid != "a168")
            continue;
        captureSession = new QMediaCaptureSession(this);
        pCamera = new QCamera(camera_device);
        captureSession->setCamera(pCamera);
        pGraphyScene = new QGraphicsScene(0, 0, 640, 480);
        pGraphyView = new QGraphicsView(this);
        pGraphyView->setScene(pGraphyScene);
        pGraphyVideoItem = new QGraphicsVideoItem;
        pGraphyVideoItem->setSize(QSizeF(640, 480));
        pGraphyVideoItem->setPos(0, 0);
        pGraphyScene->addItem(pGraphyVideoItem);
        captureSession->setVideoOutput(pGraphyVideoItem);
        pImageCapture = new QImageCapture((QObject *)pCamera);
        captureSession->setImageCapture(pImageCapture);
        QObject::connect(pImageCapture, SIGNAL(imageAvailable(int, const QVideoFrame &)), this, SLOT(onCaptureVideoFrame(int, const QVideoFrame &)));
        QObject::connect(pImageCapture, SIGNAL(imageCaptured(int, const QImage &)), this, SLOT(onCaptureImage(int, const QImage &)));
        pCamera->start(); // live play.
        QString title = camera_device.description() + " 0x" + QString::number(myDeviceDetectionData.devicePid, 16);
        setWindowTitle(title);
        break;
    }
}