MoviePy - getting progress bar values

I am running a python script which converts a video file to a audio clip using moviepy.

def convert(mp3_file,mp4_file):

    videoclip = VideoFileClip(mp4_file)
    audioclip = videoclip.audio
    audioclip.write_audiofile(mp3_file)
    audioclip.close()
    videoclip.close()

I found out that Moviepy uses a library called Proglog to print a command line progress bar.

How do I get these process completion percentage values?

from MoviePy - getting progress bar values