opencv设置采集视频分辨率方式

#include <opencv2\opencv.hpp> 
 
#include<ctime>
using namespace cv; 
using namespace std;
 
int main( ) 
{ 
	//【1】从摄像头读入视频
	VideoCapture capture(0);
 
	//【2】循环显示每一帧
	int j=0;
 
	 capture.set(CV_CAP_PROP_FRAME_WIDTH, 1080); 
  capture.set(CV_CAP_PROP_FRAME_HEIGHT,720); 
	while(1&&(j<100)) 
	{  clock_t start,finish;
    start=clock();
		j++;
		Mat frame; //定义一个Mat变量，用于存储每一帧的图像
		captureframe; //读取当前帧
		imshow("读取视频",frame); //显示当前帧
		cout<<frame.size()<<endl;
		imwrite("1.jpg",frame);
		finish=clock();
 
    cout << finish-start  << "/" << CLOCKS_PER_SEC << " (s) "<< endl;
		waitKey(1); //延时30ms
	} 
	return 0;   
}