title: How to make USB camera work with OpenCV?
body: <p>I copied code from <a href="https://stackoverflow.com/a/34588758/210342">https://stackoverflow.com/a/34588758/210342</a> and used with default (built-in) camera, it worked. Then I attached USB camera, tested it with VLC and changed the code to open camera <code>1</code>:</p>
  
  <pre><code>cam = cv2.VideoCapture(1)
  </code></pre>
  
  <p>I check whether the camera is open <code>cam.isOpened()</code> -- it is -- but the camera is not enabled (its hardware indicator, LED, is off) and indeed all I see on the screen is black frame.</p>
  
  <p>Is there some extra special code to add in order to enable USB camera?</p>