title: Opencv recorded video is too slow and camera update is very slow
body: <p>Please help me understand why video recorded using Opencv is so slow. It does not reflect quick movements.
  For example, if I move the camera then the movement is too slow in the video. Also, though I showed a picture in front of the camera for about 2 seconds, I did not see the picture in the recording.</p>
  
  <p>Can someone explain me please what is going on here.
  This is my simple code:</p>
  
  <pre><code>fourcc = cv2.VideoWriter_fourcc(*'XVID')
  out = cv2.VideoWriter('output2.avi',fourcc, 30.0, (640,480))
  
  while (True):
  
      camera.capture(stream, use_video_port=True, format='jpeg') 
      stream.seek(0)
      imageData = np.fromstring(stream.getvalue(), dtype=np.uint8)
      npImage = cv2.imdecode(imageData, 1) 
      out.write(npImage)
      stream.close()
  </code></pre>