Qstreamer.cpp

Qstreamer

The main while loop checks that both files (SWAP_IMG_FILE and SWAP_RDY_FILE ) are present.
If one or both are present, MainEvent.cpp has not yet processed the image.
Until then, Qstreamer captures frames without doing anything with them. This way, latency stays low.
Once both files are deleted by MainEvent, Qstreamer sends the most recent frame by storing it in SWAP_IMG_FILE.
The empty file SWAP_RDY_FILE is created after this save completes.
MainEvent waits for SWAP_RDY_FILE to be present. Now the whole frame is saved and ready to read.
Without this mechanism, MainEvent can easily make mistakes while reading images still written.

#include <opencv2/opencv.hpp>
#include "General.h"
#include "Settings.h"
#include "OkFile.h"

//----------------------------------------------------------------------------------
using namespace cv;
using namespace std;
//---------------------------------------------------------------------------

TSettings Settings(SETTING_FILE);        //the settings (they are loaded here for the first time)

//----------------------------------------------------------------------------------
int main()
{
    Mat frame;
    Mat norm_frame;
    ofstream Fdone;
    bool FrameError=false;

    if(!Settings.Loaded){
        OkFileShow();
        return -1;
    }

    VideoCapture cap(VIDEO_FILE, CAP_FFMPEG);

    if(!cap.isOpened()){ FrameError=true; goto Ferr; }

    if (!cap.read(frame)) { FrameError=true; goto Ferr; }

    cout << "Camera start streaming...." << endl;
    //reset lock mechanism
    unlink(SWAP_IMG_FILE);
    unlink(SWAP_RDY_FILE);

    while(true)
    {
        //wait until ready
        while(FileExists(SWAP_IMG_FILE) || FileExists(SWAP_RDY_FILE)) cap.read(frame);
        //event app is ready to recieve a new frame
        cap.read(frame);
        cv::resize(frame, norm_frame, cv::Size(320, 240));
        imwrite(SWAP_IMG_FILE,norm_frame);
        //signal image to file writing is done
        Fdone.open(SWAP_RDY_FILE);
        Fdone.close(); //write empty file
    }

    cap.release();

Ferr:
    if(FrameError) cout << "Failed to open camera. Is your ffmpeg pipeline active?" << endl;

    return 0;
}
//----------------------------------------------------------------------------------