title: Opencv cvCaptureFromCAM not loading any frame
body: <p>I am trying to implement Face detection using opencv using the sample code given in <a href="http://opencv.willowgarage.com" rel="nofollow">http://opencv.willowgarage.com</a> but cvCaptureFromCAM doesnt load any frame from webcam.I get a window dialog to select my webcam but it doesnt load any frame..</p>
  
  <pre><code>  #include "opencv2/objdetect/objdetect.hpp"
    #include "opencv2/highgui/highgui.hpp"
    #include "opencv2/imgproc/imgproc.hpp"
    #include &lt;opencv/cv.h&gt;
    #include &lt;iostream&gt;
    #include &lt;stdio.h&gt;
     using namespace std;
     using namespace cv;
  
    /** Function Headers */
  void detectAndDisplay( Mat frame );
  
   /** Global variables */
  String face_cascade_name = "haarcascade_frontalface_alt.xml";
  String eyes_cascade_name = "haarcascade_eye_tree_eyeglasses.xml";
  CascadeClassifier face_cascade;
  CascadeClassifier eyes_cascade;
  string window_name = "Capture - Face detection";
  RNG rng(12345);
  
  /** @function main */
  int main( int argc, const char** argv )
  {
  CvCapture* capture;
  Mat frame;
  
    //-- 1. Load the cascades
   if( !face_cascade.load( face_cascade_name ) ){ printf("--(!)Error loading\n"); return           -1; };
  if( !eyes_cascade.load( eyes_cascade_name ) ){ printf("--(!)Error loading\n"); return  -1; };
  
   //-- 2. Read the video stream
   capture = cvCaptureFromCAM( -1 );
  
    if( capture )
    {
     while( true )
     {
       cout&lt;&lt;"hello";
    frame = cvQueryFrame( capture );
  
     //-- 3. Apply the classifier to the frame
     if( !frame.empty() )
    { detectAndDisplay( frame ); }
    else
    { printf(" --(!) No captured frame -- Break!"); break; }
  
    int c = waitKey(10);
    if( (char)c == 'c' ) { break; }
     }
     }
     else
     {cout&lt;&lt;"noframe";}
     return 0;
     }
  
      /** @function detectAndDisplay */
     void detectAndDisplay( Mat frame )
       {
     std::vector&lt;Rect&gt; faces;
     Mat frame_gray;
  
     cvtColor( frame, frame_gray, CV_BGR2GRAY );
     equalizeHist( frame_gray, frame_gray );
  
    //-- Detect faces
     face_cascade.detectMultiScale( frame_gray, faces, 1.1, 2, 0|CV_HAAR_SCALE_IMAGE,        Size(30, 30) );
  
    for( int i = 0; i &lt; faces.size(); i++ )
   {
    Point center( faces[i].x + faces[i].width*0.5, faces[i].y + faces[i].height*0.5 );
    ellipse( frame, center, Size( faces[i].width*0.5, faces[i].height*0.5), 0, 0, 360,  Scalar( 255, 0, 255 ), 4, 8, 0 );
  
   Mat faceROI = frame_gray( faces[i] );
   std::vector&lt;Rect&gt; eyes;
  
   //-- In each face, detect eyes
    eyes_cascade.detectMultiScale( faceROI, eyes, 1.1, 2, 0 |CV_HAAR_SCALE_IMAGE, Size(30, 30) );
  
    for( int j = 0; j &lt; eyes.size(); j++ )
    {
    Point center( faces[i].x + eyes[j].x + eyes[j].width*0.5, faces[i].y + eyes[j].y + eyes[j].height*0.5 );
     int radius = cvRound( (eyes[j].width + eyes[j].height)*0.25 );
    circle( frame, center, radius, Scalar( 255, 0, 0 ), 4, 8, 0 );
    }
    }
    //-- Show what you got
    imshow( window_name, frame );
     }
  </code></pre>
  
  <p>but my program only prints noframe..Also.I am using qtcreator .</p>