python-ffmpeg merging video and sound files

merge-video-and-sound.py

# I had mistakenly downloaded some video fiels without sound so then after I had to download the sound files related but
# how could I merge them to finally have a single file? following code would this!

# !attention this file has to be inside the directory where the video and sound exists -
#   and the result would be in a sub-directory named `output`

import os
from os import listdir
from os.path import isfile, join

mypath = '.'
onlyfiles = [f for f in listdir(mypath) if isfile(join(mypath, f))]
mp4s = [f.split('.')[:-1] for f in onlyfiles if f.split('.')[-1] == 'mp4']


def path_creator(string):
    string = string.replace(' ', '\ ')
    string = string.replace('#', '\#')
    string = string.replace('&', '\&')
    return string

os.system('mkdir output')

for f in mp4s:
    os.system(
        f'ffmpeg -i ./{path_creator(str(*f))}.mp4 -i ./{path_creator(str(*f))}.webm -c copy ./output/{path_creator(str(*f))}.mp4')