title: Download audio from YouTube using pytube
body: <p>I'm using pytube and Python 3.5 to download videos from YouTube but I need to convert the videos to audio with an .avi extension.</p>
  
  <p>Here is my code that I'm currently working with:</p>
  
  <pre><code>from pytube import YouTube
  
  yt = YouTube(str(input("Enter the video link: ")))
  videos = yt.get_videos()
  
  s = 1
  for v in videos:
      print(str(s)+". "+str(v))
      s += 1
  
  n = int(input("Enter the number of the video: "))
  vid = videos[n-1]
  
  destination = str(input("Enter the destination: "))
  vid.download(destination)
  
  print(yt.filename+"\nHas been successfully downloaded")
  </code></pre>
  
  <p>In the code above I can download a video. </p>
  
  <p>My question is: How can I directly download the audio of a video on YouTube with an extension of <code>.avi</code>?</p>
  
  <p>Can YouTube Data API help me download exclusively the audio? </p>