title: How to use ffmpeg in a python function
body: <p>I have tried to use a ffmpeg to extract an audio from a video file and this is my code</p>
  
  <pre><code>import io
  import os
  import subprocess
  
  def extract_audio(video,output):
      command = "ffmpeg -i '{video}' -ac 1  -f flac -vn '{output}'"
      subprocess.call(command,shell=True)
  
  extract_audio('dm.MOV','dm-new.flac')
  </code></pre>
  
  <p>And I got no error after compiled. By doing this I should get a new file which is 'dm-new.flac'. But there is no such a flac file created after I compile the script. I think there are something wrong with the syntax or something in the variable 'command' which I have no idea to fix this. My question here is how can I use ffmpeg in a python function base on this code?</p>
  
  <p>By the way, I knew that I could just use ffmpeg without writing a function. But I really need to write in in a function. Thank you</p>