A friend from work is saying that it's useful for previously downloaded PornHub movies.

MP4toAVI.movies.converter.py

# Just a simple tool to convert mp4 files to avi.
import os
import subprocess
import glob

path = '.'
 
files = glob.glob('*.mp4')
files_count = len(files)
for index, name in enumerate(files, start=1):
    raw_filename = name[:-4]
    print("Converting file {} of {}: {}".format(index, files_count, raw_filename))
    input_file = raw_filename + '.mp4'
    out_file = raw_filename + '.avi'
    subprocess.call(["ffmpeg", "-i", input_file, "-vcodec", "copy", "-acodec", "copy", out_file])
    os.remove(input_file)