Boost/OpenCV error: no match for call to '(boost::_mfi::dm<void(cv::Mat*, cv::VideoCapture*), Recorder>)

Question

I'm want to achieve a "smooth" video recording using OpenCV and the Boost libaries. For that i'm trying to implement the code I found here in to my program. I'm not too familiar with Boost yet and I keep getting the error \\bind.hpp:313: error: no match for call to '(boost::_mfi::dm) (cv::Mat*&, cv::VideoCapture*&)' unwrapper::unwrap(f, 0)(a[base_type::a1_], a[base_type::a2_]);

My code is the following:

#include "recorder.h"
#include <iostream>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include "boost/thread.hpp"


using namespace cv;
using namespace std;
using namespace boost::posix_time;

Recorder::Recorder(){ 

     webcamRecorder.open(1);
     webcamRecorder.set(CV_CAP_PROP_FRAME_WIDTH, 1920);
     webcamRecorder.set(CV_CAP_PROP_FRAME_HEIGHT, 1080);
     recordingCount=0;
     filename = "F:/MyVideo";
     ext=".avi";
     hasStarted=false;  
}

void Recorder::captureFunc(Mat *matRecorder, VideoCapture *webcamRecorder){
      for(;;){
            //capture from webcame to Mat frame
            (*webcamRecorder) >> (*matRecorder);
            resize(*matRecorder,matOut,Size(1280,720),0,0,INTER_LINEAR);
        }
}
void Recorder::setup(){
    if (!hasStarted){
        this->start();
        boost::thread captureThread(&Recorder::captureFunc, &matRecorder, &webcamRecorder);

    }
}
void Recorder::run(){
    cout << "++++++++recorder thread called+++" << endl;

    theVideoWriter.open(filename+countAsString+ext,CV_FOURCC('L','A','G','S'), 30, Size(1280,720), true);

    nextFrameTimestamp = microsec_clock::local_time();
    currentFrameTimestamp = nextFrameTimestamp;
    td = (currentFrameTimestamp - nextFrameTimestamp);    

    if ( theVideoWriter.isOpened() == false ){
        cout << "ERROR: Failed to write the video" << endl;
    }
    if (recording){
        while(recording){
            hasStarted=true;
            while(td.total_microseconds() < 1000000/30){
            //determine current elapsed time
                currentFrameTimestamp = microsec_clock::local_time();
                td = (currentFrameTimestamp - nextFrameTimestamp);
            }

            //       determine time at start of write
            initialLoopTimestamp = microsec_clock::local_time();

            theVideoWriter << matOut; // write video file

            nextFrameTimestamp = nextFrameTimestamp + microsec(1000000/30);
            td = (currentFrameTimestamp - nextFrameTimestamp);

            finalLoopTimestamp = microsec_clock::local_time();
            td1 = (finalLoopTimestamp - initialLoopTimestamp);
            delayFound = td1.total_milliseconds();
            cout << delayFound << endl;

        }
    }
    hasStarted=false;
    cout << "finished recording" << endl;
    theVideoWriter.release();
    recordingCount++;
    countAsString = static_cast<ostringstream*>( &(ostringstream() << recordingCount) )->str();

}
void Recorder::setRecording(bool x){ recording = x;}

What is wrong with my implementation? Again the original code pieces are from here

Answer 1

The problem, and the difference between your case and the link you provided, is that you use an object method for the thread function. Specifically:

boost::thread captureThread(&Recorder::captureFunc, &matRecorder, &webcamRecorder);

An object method needs a pointer for this . Since you create the thread in an object method, you can use its this pointer:

boost::thread captureThread(&Recorder::captureFunc, this, &matRecorder, &webcamRecorder);

Some general suggestions:

1. You don't need boost for threads anymore. C++11 has it in its standard library. I suggest you use it if you can.
2. The thread you created becomes detached - it continues executing, but you can't control it. You probably want to save it somewhere, so you can join it later.

To have the thread as an instance variable:

1. Have the thread declared in the class definition: std::thread captureThread; .

2. Have it initialized in the current function, and moved to the instance variable:

   std::thread localCaptureThread(&Recorder::captureFunc, this, &matRecorder, &webcamRecorder); captureThread = std::move(localCaptureThread);