Can't grab frame from webcamera - opencv

Question

I am using OpenCV 2.4.6, VS2010 with Windows 7 64 bit. I could not grab frame from the camera. The code below is working fine for avi file, but not working to capture from camera. Can anyone help me, how can I capture the frame? Thanks in advance.......
Actually problem in this portion:
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 file" << endl;
break;
}
The full source code:
#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 file" << 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"
while(1)
{
Mat frame;
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 file" << 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 1

You should read the first frame before using while loop like this:
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 file" << 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;
}
}