python colour palette to photoshop act colour table

import subprocess
from PIL import Image

# create the palette using ffmpeg
ffmpeg_command = [
    "ffmpeg",
    "-y",
    "-i", "input.mp4",
    "-vf", "palettegen",
    "palette.png"
]
subprocess.run(ffmpeg_command)

# open the image, convert to RGB mode if necessary
img = Image.open('palette.png')
img = img.convert('RGB')
# create list of all colours in the image
# no more than 256 colours because that's the most colours a gif can have
colours = img.getcolors(maxcolors=256)

# extract the RGB tuples from the colours list
colour_list = [colour[1] for colour in colours]

# if there are less than 256 colours in the list, add black until there are 256
while len(colour_list) < 256:
    colour_list.append((0, 0, 0))

# save the colour palette as a .act colour table
with open('palette.act', 'wb') as f:
    for colour in colour_list:
        f.write(bytes(colour))
    # .act files need to have exactly 768 bytes (256 colours * 3 bytes per colour)
    # so, if the file is smaller than that, add zeroes until it's good
    # we shouldn't hit this code if the previous while loop does its job but just in case
    while f.tell() < 768:
        f.write(b'\x00')