These are my notes on editing MP4 metadata using Python Mutagen. I found most of it not straight forward and it's required a lot of research, trial, and error.

mp4meta.py

# pip install mutagen

from mutagen.mp4 import MP4, MP4Cover

video = MP4('video.mp4')
# set a TV show series name
video['tvsh'] = "TV SHOW NAME"
# set the episode title
video['\xa9nam'] = "EPISODE TITLE"
# set the video type to a TV Show
video['stik'] = [10]
# set episode number
video['tves'] = [1]
# set season number
video['tvsn'] = [1]
# set the movie rating to G
video['----:com.apple.iTunes:iTunEXTC'] = b'mpaa|G|100|'
# set the thumbnail artwork
with open('thumb.png', 'rb') as fh:
    img = fh.read()
mpv['covr'] = [MP4Cover(img, imageformat=MP4Cover.FORMAT_PNG)]
video.save()

# Movie Ratings
# - mpaa|Not Rated|000|
# - mpaa|G|100|
# - mpaa|PG|200|
# - mpaa|PG-13|300|
# - mpaa|R|400|
# - mpaa|NC-17|500|
# - mpaa|Unrated|900|
# 
# TV Ratings
# - `us-tv|TV-Y|100|` (G)
# - `us-tv|TV-Y7|200|` (PG)
# - `us-tv|TV-G|300|` (PG-13)
# - `us-tv|TV-PG|400|` (R)
# - `us-tv|TV-14|500|` (NC-17)
# - `us-tv|Unrated|900|` (Unrated)
# - `us-tv|Not Rated|000|` (Not Rated)
# 
# Media Types
# stik 0 == Home Movie
# stik 6 == Music Video
# stik 9 == Movie
# stik 10 == TV Show

# https://mutagen.readthedocs.io/en/latest/api/mp4.html
# https://stackoverflow.com/a/52413955/7341009
# https://github.com/quodlibet/mutagen/issues/391