to extract video and move into the newfolder [closed]

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My task to extract the video of 1min before using after trigger here trigger is passing when->it contains datetimeformat(190425132148).I need to convert this format into minute and subtract formatted minute with 1min(21-1) therfore result will be 20:00 the video play from 20:00 and ends in 21:00 exactly 1minute video have to take and save in separate folder but .and I record video for every 5 minutes.I have no idea about this extraction. Below is the code,

   tm exampleTime() 
   {

struct tm tm;

strptime("2019-04-09 14:28:16", "%Y-%m-%d %H:%M:%S", &tm);

return tm;
}

int main() {

    struct tm when;
when = exampleTime();

VideoCapture obj;
Mat frame;

obj.open(recordVideo->getVideoFile(when));

while(obj.read(frame)) {

    imshow("A", frame);

    char exitKeyPress = (char)waitKey(500);   //to terminate
    if( exitKeyPress == ESC_KEY_PRESSED )
        break;
}
obj.release();