docs: def extract_audio(filename, channels=1, rate=16000):
      """
      Extract audio from an input file to a temporary WAV file.
      """
      temp = tempfile.NamedTemporaryFile(suffix='.wav', delete=False)
      if not os.path.isfile(filename):
          print("The given file does not exist: {}".format(filename))
          raise Exception("Invalid filepath: {}".format(filename))
      if not which("ffmpeg"):
          print("ffmpeg: Executable not found on machine.")
          raise Exception("Dependency not found: ffmpeg")
      command = ["ffmpeg", "-y", "-i", filename,
                 "-ac", str(channels), "-ar", str(rate),
                 "-loglevel", "error", temp.name]
      use_shell = True if os.name == "nt" else False
      subprocess.check_output(command, stdin=open(os.devnull), shell=use_shell)
      return temp.name, rate