Record video of a certain time using OpenCV in C++

Question

I'm working on image processing (OpenCC 3.0, C++).

Actually, what I am trying to do is:

1. Record Video as a 1 minute (that's my question)
2. After recording video, read recorded video (I will do this step after first step is solved)
3. Do necessary image processing process (I already did this step)
4. Go back to state 1 and do same process until getting to the finish order.

I am attaching code for state 1 . (This code, record video and write on file until press ESC key.)

Could you help me, how can I record video for 1 minute or 10 minutes or any specific time?

I want to record videos for 1 minute period.

#include "opencv2/opencv.hpp"
#include <iostream>

using namespace std;
using namespace cv;

int main() {

    VideoCapture vcap(0);
    if (!vcap.isOpened()) {
        cout << "Error opening video stream or file" << endl;
        return -1;
    }

    int frame_width = vcap.get(CV_CAP_PROP_FRAME_WIDTH);
    int frame_height = vcap.get(CV_CAP_PROP_FRAME_HEIGHT);
    VideoWriter video("/MyVideo.avi", CV_FOURCC('M', 'J', 'P', 'G'), 10, Size(frame_width, frame_height), true);

    for (;;) {

        Mat frame;
        vcap >> frame;
        video.write(frame);
        imshow("Frame", frame);
        char c = (char)waitKey(33);
        if (c == 27) break;
    }
    return 0;
}`

That's working.

Here is my code. I was trying to get 10 seconds videos in my last code, but I got 16 seconds videos. Can you explain why that is?

#include "opencv2/opencv.hpp"
#include <iostream>
#include <ctime>
#include <cstdio>
#include <time.h>
#include <stdio.h>

    using namespace std;
    using namespace cv;

    int main() {

        //////////////////// Added Part
        time_t start, end;
        //////////////////// Added Part
        VideoCapture vcap(0);
        if (!vcap.isOpened()) {
            cout << "Error opening video stream or file" << endl;
            return -1;
        }
        int frame_width = vcap.get(CV_CAP_PROP_FRAME_WIDTH);
        int frame_height = vcap.get(CV_CAP_PROP_FRAME_HEIGHT);
        VideoWriter video("C:\\Users\\lenovo\\Desktop\\OpenCV Webcam Video Record With R Key\\WebcamRecorder\\WebcamRecorder\\data\\MyVideo.avi", CV_FOURCC('M', 'J', 'P', 'G'), 10, Size(frame_width, frame_height), true);

        //////////////////// Added Part
        time(&start);
        //////////////////// Added Part

        for (;;) {

            Mat frame;
            vcap >> frame;
            video.write(frame);
            imshow("Frame", frame);
            char c = (char)waitKey(33);
            if (c == 27) break;

            //////////////////// Added Part
            time(&end);
            double dif = difftime(end, start);
            printf("Elasped time is %.2lf seconds.", dif);
            if (dif==10)
            {
                std::cout << "DONE" << dif<< std::endl;
                break;
            }
            //////////////////// Added Part
        }
        return 0;
    }

Answer 1

how can I record video 1 min or 10 min or any certain time?

Just before the for loop start a clock to get the current time and store it to a variable called start_time .

Just below this code inside the for loop

char c = (char)waitKey(33);
        if (c == 27) break;

Use another variable to get current time, name it cur_time .

Subtract start_time from cur_time to get time elapsed. If you see that it reaches the time using a if condition then break the loop .

Don't declare the cur_time variable inside for loop , declare it before.

You can use this reference Easily measure elapsed time