docs: def _add_subtitles(self, subtitles):
          '''Adds subtitles to playing video.
  
          :param subtitles: A URL to a remote subtitles file or a local filename
                            for a subtitles file.
  
          .. warning:: You must start playing a video before calling this method
                       or it will loop for an indefinite length.
          '''
          # This method is named with an underscore to suggest that callers pass
          # the subtitles argument to set_resolved_url instead of calling this
          # method directly. This is to ensure a video is played before calling
          # this method.
          player = xbmc.Player()
          for _ in xrange(30):
              if player.isPlaying():
                  break
              time.sleep(1)
          else:
              raise Exception('No video playing. Aborted after 30 seconds.')
  
          player.setSubtitles(subtitles)