>>> from pytube import YouTube
 >>> YouTube('https://youtu.be/2lAe1cqCOXo').streams.first().download()
 >>> yt = YouTube('http://youtube.com/watch?v=2lAe1cqCOXo')
 >>> yt.streams
  ... .filter(progressive=True, file_extension='mp4')
  ... .order_by('resolution')
  ... .desc()
  ... .first()
  ... .download()