title: javacv: grabber.getFrameRate() return 0
body: <p>I have used javacv for my project to deal with avi.
  The video shows faster than normal, I want to get the fps to set the speed of the video. But grabber.getFrameRate() return 0, as the same with grabber.getLengthInFrames() and grabber.getSampleRate(), can anyone tell me why?
  code snippet below:</p>
  
  <pre><code>FrameGrabber grabber = new OpenCVFrameGrabber("sample.avi");
  double fps=grabber.getFrameRate();
  System.out.println(fps);
  //int n=grabber.getLengthInFrames();
  //int f=grabber.getSampleRate();
  CvMemStorage storage = CvMemStorage.create();
  grabber.start();
  grabbedImage = grabber.grab();
  while (frame.isVisible() &amp;&amp; (grabbedImage = grabber.grab()) != null)
  {
          BufferedImage bfimg = grabbedImage.getBufferedImage();        
          frame.showImage(bfimg);
          frame.waitKey((int)(1000/fps));            
          cvClearMemStorage(storage);
  }
  grabber.stop();
  </code></pre>