VideoCapture stutters when I use cap.set

1

Hello,
I’m a beginner in programming and bad at English. But I hope that you will help me with my problem.

I open a video in my program and play it in a window.
A video camera is also running, which I evaluate.
If I don’t want to play the video from the beginning, it stutters (activate **********).
Later I would like to repeat the last 3 seconds of the video during an action from the camera. Then I want to repeat the last three seconds again in slow motion.

I hope I have explained this clearly and you can help me.

(I use Rasbian on a Raspberry Pi 4b / 8Gb)

Many Thanks,

Achim

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

using namespace cv;
using namespace std;

//int zaehler= 200; //****************************************** Begin at frame 200

int main()
{
    VideoCapture capCam = VideoCapture(0); 
    VideoCapture capVid = VideoCapture("SW-3.mpeg");
    namedWindow("video", WINDOW_NORMAL);
    resizeWindow("video", 1300,700);
    moveWindow("video", 1950,0);
    while(waitKey(1) !='q')
    {
        Mat BildVid;
        Mat BildCam;
        Mat bgr[3];
        double min_val, max_val;
        Point minLoc, maxLoc;
        //double scalar;

        capCam.read(BildCam);
        //capVid.set(1,zaehler);//****************************
        //zaehler++;//**********************************
        capVid.read(BildVid);
        if(!BildCam.empty())
        {
            split(BildCam, bgr);
            //imshow(image, bgr[2]);
            //cvtColor(image, gray, COLOR_BGR2GRAY);

            minMaxLoc( bgr[2], &min_val, &max_val, &minLoc, &maxLoc);
            if(max_val>250)
            {
            std::cout<<"maxLoc, maxVal = "<<maxLoc<<", "<<max_val<<std::endl;

            circle (BildVid, maxLoc, 5, Scalar(0, 0, 255), 3, LINE_AA);
            }
            imshow("video", BildVid);
            //imshow("camera", BildCam);
        }
        }
}
2

use cv::CAP_PROP_POS_FRAMES instead of 1

this would “seek”. that’s an expensive and complex operation in general, and it isn’t always precise.

I would recommend doing that once, and then simply read.

3

Outstanding! It works now!

Many Thanks