OpenCV can't capture the frame from the webcam

Question

I am using OpenCV 2.4.6 with VS2010.

I think my webcam can't capture the frame. When I executed the code it built successfully, but I am not getting output. I think, when I check if(!bSuccess) it is executed and can't capture frame from the webcam.

How can I resolve this problem? My code is below:

#include "opencv2/highgui/highgui.hpp"
#include 

using namespace cv;
using namespace std;

int main(int argc, char* argv[])
{
    VideoCapture cap(0); // open the video camera no. 0

    if (!cap.isOpened())  // if not success, exit program
    {
    cout  &lt&lt "Cannot open the video file" &lt&lt endl;
        return -1;
    }

   double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
   double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the  video
    cout &lt&lt "Frame size : " &lt&lt dWidth &lt&lt " x " &lt&lt dHeight &lt&lt endl;
    namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
    while (1)
    {
       Mat frame;
       bool bSuccess = cap.read(frame); // read a new frame from video
       if (!bSuccess) //if not success, break loop
        {
         cout &lt&lt "Cannot read a frame from video file" &lt&lt endl;
            break;
        }

        imshow("MyVideo", frame); //show the frame in "MyVideo" window

        if (waitKey(30) == 27) 
        {
        cout &lt&lt "esc key is pressed by user" &lt&lt endl;
          break; 
        }
    }
    return 0;

}

Answer 1

add this line cap.retrieve(frame);

before line with bool bSuccess = cap.read(frame);

Answer 2

Fixing the VideoCapture failing

in some openCV libs the VideoCapture cap(0);bool bSuccess = cap.read(frame); will first return an 0. So for in a while(1) loop it will fail at the first iteration. So you need to run the cap.read(frame); line one time before entering into your infinite loop

#include "opencv2/highgui/highgui.hpp"
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char* argv[])
{
    VideoCapture cap(0); // open the video camera no. 0

    if (!cap.isOpened())  // if not success, exit program
    {
        cout << "Cannot open the video cam" << endl;
        return -1;
    }

   double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
   double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video

    cout << "Frame size : " << dWidth << " x " << dHeight << endl;

    namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"

    Mat frame;
cap.read(frame);

while (1)
{

    bool bSuccess = cap.read(frame); // read a new frame from video

     if (!bSuccess) //if not success, break loop
    {
         cout << "Cannot read a frame from video stream" << endl;
         break;
    }

    imshow("MyVideo", frame); //show the frame in "MyVideo" window

    if (waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
   {
        cout << "esc key is pressed by user" << endl;
        break;
   }
}
return 0;

}

Answer 3

Try without this part of your code:

double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the  video
cout << "Frame size : " << dWidth << " x " << dHeight << endl;
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"

or try to get at least one frame from camera before getting or setting camera properties - i think that on Windows camera in opencv isn't fully optimized before getting first frame.

Alternatively you may try to use different API - see ma answer here: OpenCV on Mac is not opening USB web camera

Answer 4

not only first, but many other frames can be skipped ;-)

opencv 2.4.9 visual studio 10

#include <iostream>
#include <opencv2\core\core.hpp>
#include <opencv2\highgui\highgui.hpp>

using namespace std;
using namespace cv;

int main()
{
 VideoCapture webcam_0(0);                    //open stream
 if(!webcam_0.isOpened())
 {
  cout << "error: cannot open stream between webcam_0 and application" << endl;
  waitKey(0);
  return -1;
 }

 Mat frame;                                   //Mat header for frame storing from webcam_0
 int i = 0;                                   //index, we use it for testing
 
 while ((i++ < 100) && !webcam_0.read(frame)) //skip unread frames
 {
  cout << "frame " << i << " skipped" << endl;
 }

 if (i >= 100)                                //check webcam_0 failure
 {
  cout << "cannot read frames from webcam_0, check drivers" << endl;
  waitKey(0);
  return -1;
 } else
 {
  cout << "cam is ready" << endl;
 }

 char * window_name = "webcam_0 test; press \"ESC\" to exit";
 namedWindow(window_name, CV_WINDOW_AUTOSIZE);//make new window
 imshow(window_name, frame);                  //output 1st successfully read frame
 waitKey(10);
 
 while(1)                                     //reading frames from webcam_0
 {
  if(!webcam_0.read(frame))
  {
   cout << "cannot get frame from webcam_0, check drivers" << endl;
   waitKey(0);
   return -1;
  }
  imshow(window_name, frame);

  if (waitKey(10) == 27)                   //check if ESC is pressed
  {
   cout << "bye!" << endl;
   waitKey(0);
   break;
  }
 }
 return 0;
}

Answer 5

try the following code:

#include "stdafx.h"
#include "highgui\highgui.hpp"  

using namespace cv;


void main()
{
    Mat Frame;

    VideoCapture cap(0);  // change the number to 1 for an external USB webcam

    while(1)
    {
        cap >> Frame;
        imshow("Camera Feed", Frame);

        if (waitKey(10) == 27)  return;
    }
}

Answer 6

Remove the "cv_" in all the cases similar to those mentioned below:

double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT);

It worked for me.