下面这行代码是获取摄像头每帧的时间戳：

        double timestamp = cap.get(cv::CAP_PROP_POS_MSEC);

改变帧率的方法是：

cap.set(cv::CAP_PROP_FPS, 30);   //帧率改为30

但是实际测试时发现帧率并未被改变，这个可能和VideoCapture cap(cv::CAP_V4L2)有关，cv::CAP_V4L2只是其中一种读取方法，这个参数可能需要和相机采用的驱动方法有关。

编译：

g++ camera_data.cpp -lopencv_core -lopencv_highgui -lopencv_imgcodecs -lopencv_videoio

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>

#include <time.h>

using namespace std;

// OpenCV includes
#include "opencv2/core.hpp"
#include "opencv2/highgui.hpp"
using namespace cv;

int main(int argc, const char** argv)
{
	// 1.创建视频采集对象;
	VideoCapture cap(cv::CAP_V4L);
	// 2.打开默认相机;
	cap.open(0);
	 
	int curFPS=cap.get(cv::CAP_PROP_FPS);
	cout<< "FPS: "<< curFPS<<endl;

	cap.set(cv::CAP_PROP_FPS, 30);
	int curFpsSet=cap.get(cv::CAP_PROP_FPS);
	cout<< "set FPS: "<< curFpsSet<<endl;

	// 3.判断相机是否打开成功;
	if (!cap.isOpened())
		return -1;

	namedWindow("Video", 1);


	for (;;)
	{
		// 获取新的一帧;
		Mat frame;

        double timestamp = cap.get(cv::CAP_PROP_POS_MSEC);
        cout<<fixed;
        cout<<"time: "<< timestamp<<endl;

		time_t end_time = time(NULL);
		printf("ctime is %s\n",ctime(&end_time)); //得到日历时间
		
		cap >> frame;
		if (frame.empty())
			return 0;

		// 显示新的帧;
		imshow("Video", frame);
        // cv::waitKey(1);

		// 按键退出显示;
		if (waitKey(3) >= 0) break;
	}

	// 5.释放视频采集对象;
	cap.release();

	return 0;
}