title: python cv2.Videocapture() does not work, cap.isOpened() returns false
body: <p>cv2.Videocapture() works fine while using webcam but while trying to read from hard drive it shows error  cap.isOpened() returns false</p>
  
  <pre><code>import cv2
  import numpy as np
  background=cv2.imread('background.png')
  cap = cv2.VideoCapture('car video.mp4')
  cap.open('car video.mp4')
  print cap.isOpened()
  while 1:
      ret,img=cap.read()
      cv2.imshow('a',img)
      print img.shape
  
  
      if cv2.waitKey(1) &amp; 0xFF == ord('q'):
          break
  
  cap.release()
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>It shows this error</p>
  
  <pre><code>    cv2.imshow('a',img)
      error: ..\..\..\..\opencv\modules\highgui\src\window.cpp:266: error:       (-215)        size.width&gt;0 &amp;&amp; size.height&gt;0 in function cv::imshow
  </code></pre>
  
  <p>my opencv version 3.0.0, python 2.7, windows10 32 bit </p>