title: cvGetCaptureProperty always return 0 for CV_CAP_PROP_FRAME_COUNT!
body: <p>This is a code snippet from O'Reilly Learning Opencv,</p>
  
  <pre><code>cvNamedWindow("Example3", CV_WINDOW_AUTOSIZE);
  g_capture = cvCreateFileCapture(argv[1]);
  int frames = (int) cvGetCaptureProperty(g_capture, CV_CAP_PROP_FRAME_COUNT);
  if (frames != 0) {
      cvCreateTrackbar("Position", "Example3", &amp;g_slider_postion, frames, onTrackbarSlide);
  }
  </code></pre>
  
  <p>But unfortunately, cvGetCaptureProperty always return 0. I have searched opencv group in Yahoo, found the same problem.</p>