windows下使用camera（opencv方式）

  一.  opencv支持读取摄像头，支持视频录制或显示， 具体代码

    //1. 初始化视频录制文件
    String recFileName = std::to_string(count) + "_rec.avi";
    int wfourcc = VideoWriter::fourcc('M', 'J', 'P', 'G');
    writer = VideoWriter(recFileName, wfourcc, CAP_FPS, Size(CAP_WIDTH, CAP_HEIGHT));

    //2. 初始化摄像头
    int apiBackend = CAP_DSHOW;
    cap = VideoCapture(count + apiBackend);

    //cap.set(CAP_PROP_SETTINGS, 1);
    int w = cap.get(CAP_PROP_FRAME_WIDTH);
    int h = cap.get(CAP_PROP_FRAME_HEIGHT);    
    int fourcc = cap.get(CAP_PROP_FOURCC);
    qDebug() << "camera origin parameters: fourcc:" << fourcc<<", width: "<<w<<", height:"<< h;

    cap.set(CAP_PROP_FRAME_WIDTH, CAP_WIDTH);
&nb