title: Opening video with openCV +python
body: <p>I using python 2.7 and openCV 2.3.1 (win 7).
  I trying open video file:</p>
  
  <pre><code>stream = cv.VideoCapture("test1.avi")
  if stream.isOpened() == False:
  print "Cannot open input video!"
  exit()
  </code></pre>
  
  <p>But I have warning:</p>
  
  <pre><code>warning: Error opening file (../../modules/highgui/src/cap_ffmpeg_impl_v2.hpp:394)
  </code></pre>
  
  <p>If use video camera (<code>stream = cv.VideoCapture(0)</code>), this code works.
  Any ideas as to what I'm doing wrong?
  Thanks a lot to all! </p>