Pushing & Popping a frame to a Mat vector - c++

Question

I am trying to grab multiple frames from 2 USB cameras using threads. Issue is i need to push frames into frame_queue vector and then pop one frame at a time from the vector for further image processing.
I followed this link
https://putuyuwono.wordpress.com/2015/05/29/multi-thread-multi-camera-capture-using-opencv/
The code in this link has used concurrent_queue.h for queuing up Mat frames but instead i want to use vector Mat to store the incoming frames.
Header file CameraStreamer.h:
#include <iostream>
#include <string>
#include <thread>
#include <vector>
//#include <concurrent_queue.h>
#include <boost/thread.hpp>
#include "opencv2/videoio.hpp"
using namespace std;
using namespace cv;
//using namespace concurrency;
class CameraStreamer{
public:
//this holds camera stream urls
vector<string> camera_source;
//this holds usb camera indices
vector<int> camera_index;
//this holds OpenCV VideoCapture pointers
vector<VideoCapture*> camera_capture;
//this holds queue(s) which hold images from each camera
vector<Mat*> frame_queue;
//this holds thread(s) which run the camera capture process
vector<thread*> camera_thread;
//Constructor for IP Camera capture
CameraStreamer(vector<string> source);
//Constructor for USB Camera capture
CameraStreamer(vector<int> index);
//Destructor for releasing resource(s)
~CameraStreamer();
private:
bool isUSBCamera;
int camera_count;
//initialize and start the camera capturing process(es)
void startMultiCapture();
//release all camera capture resource(s)
void stopMultiCapture();
//main camera capturing process which will be done by the thread(s)
void captureFrame(int index);
};
Here is my CameraStreamer.cpp:
#include "camerastreamer.h"
CameraStreamer::CameraStreamer(vector<string> stream_source)
{
camera_source = stream_source;
camera_count = camera_source.size();
isUSBCamera = false;
startMultiCapture();
}
CameraStreamer::CameraStreamer(vector<int> capture_index)
{
camera_index = capture_index;
camera_count = capture_index.size();
isUSBCamera = true;
startMultiCapture();
}
CameraStreamer::~CameraStreamer()
{
stopMultiCapture();
}
void CameraStreamer::captureFrame(int index)
{
VideoCapture *capture = camera_capture[index];
while (true)
{
Mat frame;
//Grab frame from camera capture
(*capture) >> frame;
//Put frame to the queue
frame_queue[index]->push(frame);
//relase frame resource
frame.release();
}
}
void CameraStreamer::startMultiCapture()
{
VideoCapture *capture;
thread *t;
vector<Mat> *q;
for (int i = 0; i < camera_count; i++)
{
//Make VideoCapture instance
if (!isUSBCamera){
string url = camera_source[i];
capture = new VideoCapture(url);
cout << "Camera Setup: " << url << endl;
}
else{
int idx = camera_index[i];
capture = new VideoCapture(idx);
cout << "Camera Setup: " << to_string(idx) << endl;
}
//Put VideoCapture to the vector
camera_capture.push_back(capture);
//Make thread instance
t = new thread(&CameraStreamer::captureFrame, this, i);
//Put thread to the vector
camera_thread.push_back(t);
//Make a queue instance
q = new vector<Mat>;
//Put queue to the vector
frame_queue.push_back(q);
}
}
void CameraStreamer::stopMultiCapture()
{
VideoCapture *cap;
for (int i = 0; i < camera_count; i++)
{
cap = camera_capture[i];
if (cap->isOpened()){
//Relase VideoCapture resource
cap->release();
cout << "Capture " << i << " released" << endl;
}
}
}
Main.cpp:
int main()
{
//IP camera URLs
vector<string> capture_source = {
"rtsp://192.168.2.100/profile2/media.smp",
"rtsp://192.168.0.100/profile2/media.smp"
};
//USB Camera indices
vector<int> capture_index = { 0, 1 };
//Highgui window titles
vector<string> label;
for (size_t i = 0; i < capture_index.size(); i++)
{
string title = "CCTV " + to_string(i);
label.push_back(title);
}
//Make an instance of CameraStreamer
CameraStreamer cam(capture_index);
while (waitKey(20) != 27)
{
//Retrieve frames from each camera capture thread
for (size_t i = 0; i < capture_index.size(); i++)
{
Mat *frame;
//Pop frame from queue and check if the frame is valid
cam.frame_queue[i].pushback(frame);
//Show frame on Highgui window
imshow(label[i], frame);
}
}
}
i tried using
cam.frame_queue[i].pushback(frame);
but it doesn't work.
So i am not sure how do i push and pop a frame into frame_queue vector with an index.