[OpenCV][C++] Record only the detected motion - c++

Question

I'm working on a project to detect motion on a camera.
I need to start recording video when motion is detected for example:
Record while motion is being detected
Continue recording for 10 seconds after the motion detection is stopped
I have a working example that only detects the motion and draw rectangles on the moving parts.
I searched for examples on how to record when motion is detected but no good results.
Here is my working code:
#include <iostream>
#include <sstream>
#include <opencv4/opencv2/imgproc.hpp>
#include <opencv4/opencv2/videoio.hpp>
#include <opencv4/opencv2/highgui.hpp>
#include <opencv4/opencv2/video.hpp>
#include <unistd.h>
using namespace cv;
using namespace std;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
int main(int argc, char* argv[])
{
//create Background Subtractor objects
Ptr<BackgroundSubtractor> pBackSub;
pBackSub = createBackgroundSubtractorMOG2();
VideoCapture capture(0);
if (!capture.isOpened()){
//error in opening the video input
cerr << "Unable to open: " << endl;
return 0;
}
Mat frame, fgMask;
sleep(3);
while (true) {
capture >> frame;
if (frame.empty())
break;
//update the background model
pBackSub->apply(frame, fgMask);
imshow("FG Mask", fgMask);
RNG rng(12345);
findContours(fgMask, contours, hierarchy, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE,Point(0, 0));
vector<Rect>boundRect (contours.size());
vector<vector<Point> > contours_poly( contours.size() );
for (int i = 0; i < contours.size();i++) {
if( contourArea(contours[i])< 500)
{
continue;
}
putText(frame, "Motion Detected", Point(10,20), FONT_HERSHEY_SIMPLEX, 0.75, Scalar(0,0,255),2);
approxPolyDP( contours[i], contours_poly[i], 3, true );
boundRect[i] = boundingRect( contours_poly[i] );
Scalar color = Scalar( rng.uniform(0, 256), rng.uniform(0,256), rng.uniform(0,256) );
rectangle( frame, boundRect[i].tl(), boundRect[i].br(), color, 2 );
}
imshow("Frame", frame);
int keyboard = waitKey(30);
if (keyboard == 'q' || keyboard == 27)
break;
}
return 0;
}
I tried adding this to the code:
int frameWidth = 320;
int frameHeight = 240;
cv::Size frameSize = cv::Size(frameWidth, frameHeight);
/* Output file */
int codec = cv::VideoWriter::fourcc('M', 'P', '4', 'V');
cv::VideoWriter outputVideo;
outputVideo.open("rr.mp4", codec, capture.get(cv::CAP_PROP_FPS), frameSize, true);
and after drawing the rectangle I write the frame to the video:
outputVideo.write(frame);
but after that, the video is empty and crashes.
I already took a look at Motion but I didn't find an example.
How can I achieve this?
Thanks,
Talel

Answer 1

I resolved the issue,
I was opening the output video with a specific dimensions (320,240) and I was saving the captured frame which is bigger.
So the solution is to resize the captured frame to fit into the output video.
Here is the final solution if anyone is interesting:
Turn the laptop camera into an IP camera with: cam2ip
Here is the source code:
#include <iostream>
#include <sstream>
#include <opencv4/opencv2/imgproc.hpp>
#include <opencv4/opencv2/videoio.hpp>
#include <opencv4/opencv2/highgui.hpp>
#include <opencv4/opencv2/video.hpp>
#include <unistd.h>
using namespace cv;
using namespace std;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
int main(int argc, char* argv[])
{
//create Background Subtractor objects
Ptr<BackgroundSubtractor> pBackSub;
pBackSub = createBackgroundSubtractorMOG2();
const std::string videoStreamAddress = "http://192.168.20.100:56000/mjpeg";
cv::VideoCapture vcap;
if(!vcap.open(videoStreamAddress)) {
std::cout << "Error opening video stream or file" << std::endl;
return -1;
}
Mat frame, fgMask;
int frameWidth = 320;
int frameHeight = 240;
cv::Size frameSize = cv::Size(frameWidth, frameHeight);
/* Output file */
int codec = cv::VideoWriter::fourcc('M', 'P', '4', 'V');
cv::VideoWriter outputVideo;
outputVideo.open("rr.mp4", codec, vcap.get(cv::CAP_PROP_FPS), frameSize, true);
sleep(3);
while (true) {
vcap >> frame;
if (frame.empty())
break;
//update the background model
pBackSub->apply(frame, fgMask);
imshow("FG Mask", fgMask);
RNG rng(12345);
findContours(fgMask, contours, hierarchy, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE,Point(0, 0));
vector<Rect>boundRect (contours.size());
vector<vector<Point> > contours_poly( contours.size() );
for (int i = 0; i < contours.size();i++) {
if( contourArea(contours[i])< 500)
{
continue;
}
putText(frame, "Motion Detected", Point(10,20), FONT_HERSHEY_SIMPLEX, 0.75, Scalar(0,0,255),2);
approxPolyDP( contours[i], contours_poly[i], 3, true );
boundRect[i] = boundingRect( contours_poly[i] );
Scalar color = Scalar( rng.uniform(0, 256), rng.uniform(0,256), rng.uniform(0,256) );
rectangle( frame, boundRect[i].tl(), boundRect[i].br(), color, 2 );
resize(frame, frame, frameSize);
outputVideo.write(frame);
}
imshow("Frame", frame);
int keyboard = waitKey(30);
if (keyboard == 'q' || keyboard == 27)
break;
}
outputVideo.release();
return 0;
}
Further enhancement suggestions:
Make sure that the light is not part of the motion detection
Open an output video with the same capture's dimensions