title: cv2.videoCapture() return always false, also skvideo.io.VideoCapture()
body: <p>I read nearly all of questions about this subject but I didn't solve it.
  I am working on Linux/Mint. I tried to open my webcam (or any video it does not matter) with opencv and read a frame from the video. And I write this code:</p>
  
  <pre><code>import cv2
  
  cap = cv2.VideoCapture(0)
  
  while(True):
      ret, frame = cap.read()
      print ret #It returns always false
  
      gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
  
      cv2.imshow('frame',gray)
      if cv2.waitKey(1) &amp; 0xFF == ord('q'):
         break
  
  cap.release()
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>--> I read the problem might can be because of opencv installation. I checked the installation, it seems true. When I write 'pip freeze', the result list contained <strong>opencv-python module</strong> so I thought the installation is correct and it isn't the reason for my problem.</p>
  
  <p>--> I tried to <strong>change the index</strong> in videoCapture(0) to -1 and 1, and it again failed.</p>
  
  <p>--> And then, I read that the other cause can be <strong>FFmpeg</strong> or <strong>codec</strong>. But I also installed FFmpeg and the problem didn't change.</p>
  
  <p>--> cv2.VideoCapture() didn't give any error but I want to install cv2 module on the Poject>Settings>Project Interpreter, it gave me an error (executed command: <strong>pip install cv2</strong>) But when I run this command, it gave me this error : Could not find a version that satisfies the requirement cv2 (from versions: ) No matching distribution found for cv2
  I checked the cv2 module in my virtualenv and it seems there. (/cv_env/lib/python2.7/site-packages/cv2)</p>
  
  <p>--> I also tried it with <strong>"skvideo.io.VideoCapture()"</strong> but I failed again.</p>
  
  <p>So, I didn't understand the problem and I am really new in this subject. 
  What is the problem?</p>