title: Error opening video stream or file?
body: <p>l try to read the following video, downloaded from <a href="http://www.sample-videos.com/" rel="nofollow noreferrer">http://www.sample-videos.com/</a></p>
  
  <p>which is <a href="http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_5mb.mp4" rel="nofollow noreferrer">http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_5mb.mp4</a></p>
  
  <p>Here is my code :</p>
  
  <pre><code>import cv2
  
  cap = cv2.VideoCapture('big_buck_bunny_720p_5mb.mp4')
  
  if(cap.isOpened()== False):
    print("Error opening video stream or file")
  
  
  count = 0
  
  while (cap.isOpened()):
      # capture frame by frame :
      ret, frame = cap.read()
      if ret==True:
          # Display the resulting frame
          cv2.imshow('Frame', frame)
          cv2.imwrite("frame%d.jpg" % count, frame)
          count +=1
          print(count)
  </code></pre>
  
  <p>However l get <strong>Error opening video stream or file</strong> at <code>cap = cv2.VideoCapture('big_buck_bunny_720p_5mb.mp4')</code>
  and <code>ret equals False always</code></p>
  
  <p>My OpenCV version is 3.1.0</p>