title: How I can use Kivy (Python) camera
body: <p>I try to use uix.camera widget and show some wideo from my web-camera.
  I looked into the documentation and try to use this simply code. But it's just show me a white creen withoud any video (I enabled playing). 
  What I'm doing wrong? 
  Maybe some useful docs\tutorial exist (because from official documentation I understanding a little from many). Thanks for any help.</p>
  
  <pre><code>import kivy
  kivy.require('1.9.1')
  
  from kivy.app import App
  from kivy.uix.label import Label
  from kivy.uix.camera import Camera
  
  class MainApp(App):
      def build(self):
          return Camera(play=True)
  
  if __name__== "__main__":
      MainApp().run()
  </code></pre>