C++读取视频帧保存成图片

#include<opencv2\opencv.hpp>
#include <iostream>
#include <stdio.h>
#include<fstream> 

using namespace std;
using namespace cv;



int main()
{
    //打开视频文件：其实就是建立一个VideoCapture结构  
    VideoCapture capture("D:/MyData/zhaohz4/Desktop/Nansha_video/2.mp4");   
    //检测是否正常打开:成功打开时，isOpened返回ture  
    if (!capture.isOpened())
        cout << "fail toopen!" << endl;

    //获取整个帧数  
    long totalFrameNumber = capture.get(CV_CAP_PROP_FRAME_COUNT);
    cout << "整个视频共" << totalFrameNumber << "帧" << endl;
    //设置开始帧()  
    long frameToStart = 1;
    capture.set(CV_CAP_PROP_POS_FRAMES, frameToStart);
    cout << "从第" << frameToStart << "帧开始读" << endl;


    //设置结束帧  
    int frameToStop = 4000;

    if (frameToStop < frameToStart)
    {
        cout << "结束帧小于开始帧，程序错误，即将退出！" << endl;
        return -1;
    }
    else
    {
        cout << "结束帧为：第" << frameToStop << "帧" << endl;
    }

    //获取帧率  
    double rate = capture.get(CV_CAP_PROP_FPS);
    cout << "帧率为:" << rate << endl;
    //定义一个用来控制读取视频循环结束的变量  
    bool stop = false;

    //承载每一帧的图像  
    Mat frame;

    //显示每一帧的窗口  
    namedWindow("Extractedframe");

    //两帧间的间隔时间:  
    //int delay = 1000/rate;  
    double delay = 2000 / rate;     //??


    //利用while循环读取帧  
    //currentFrame是在循环体中控制读取到指定的帧后循环结束的变量  
    long currentFrame = frameToStart;


    //滤波器的核  
    int kernel_size = 3;
    Mat kernel = Mat::ones(kernel_size, kernel_size, CV_32F) / (float)(kernel_size*kernel_size);

    while (!stop)
    {
        //读取下一帧  
        if (!capture.read(frame))
        {
            cout << "读取视频失败" << endl;
            return -1;
        }
        if (currentFrame % 3 == 0)    //每三帧保存一帧
        {
            cout << "正在读取第" << currentFrame << "帧" << endl;
            imshow("Extractedframe", frame);

            cout << "正在写第" << currentFrame << "帧" << endl;
            stringstream str;
            str << "2-"<<currentFrame << ".jpg";     //保存格式
            cout << str.str() << endl;
            imwrite(str.str(), frame);
        }

        //waitKey(intdelay=0)当delay≤ 0时会永远等待；当delay>0时会等待delay毫秒  
        //当时间结束前没有按键按下时，返回值为-1；否则返回按键  
        //int c = waitKey(delay);
        int c = waitKey(1000);
        //按下ESC或者到达指定的结束帧后退出读取视频  
        if ((char)c == 27 || currentFrame > frameToStop)
        {
            stop = true;
        }
        //按下按键后会停留在当前帧，等待下一次按键  
        if (c >= 0)
        {
            waitKey(0);
        }
        currentFrame++;

    }
    //关闭视频文件  
    capture.release();
    waitKey(0);
    return 0;
}