关于opencv采集usb摄像头，采集一帧效率低的解决办法

#include "opencv2/opencv.hpp"
#include "opencv2/highgui/highgui_c.h"
#include 
#include 
#include 

using namespace cv;

const char *g_szTitle = "Camera";
int _tmain(int argc, _TCHAR* argv[])
{

	/*opencv 2.4.1*/
	VideoCapture cap2(CV_CAP_DSHOW+1);
	
	/*
	用dshow采集USS摄像头的时候，CV_CAP_PROP_FPS一定要先设置，否则后设置会导致采取(1280*720)一帧 时间大概在80ms
	
	
	*/
	cap2.set(CV_CAP_PROP_FPS, 30);
	cap2.set(CV_CAP_PROP_FOURCC, CV_FOURCC('M','J','P','G'));
	cap2.set(CV_CAP_PROP_FRAME_WIDTH, 1280);
	cap2.set(CV_CAP_PROP_FRAME_HEIGHT, 720);
	//cap2.set(CV_CAP_PROP_FPS, 30); 后设置帧率貌似不起作用啊！！ 晕菜
	if (!cap2.isOpened())
	{
		return -1;
	}

	for (;;)
	{
		clock_t stime = clock();
		Mat imgRGB2;
		cap2 >> imgRGB2;
		clock_t endtime = clock();
		double dtimetmp =(double) (endtime - stime);
		printf("cap——time  #%Lf's.\n", dtimetmp);
		
		imshow(g_szTitle, imgRGB2);

		if (cvWaitKey(30) == 'q')
		{
			break;
		}
	}

	cvDestroyWindow(g_szTitle);
	
	return 0;
}