Extract frames from WEBM (VP9) using Python

I want to parse a .webm file in the VP9 codec using Python and no modules. I know this sounds stupid and/or useless but I have to.

I would like to have some kind of function "extract_frames" that would extract every frame of a webm. The "frame format" does not have to be anything specific, but it will ultimately be converted to a 2-dimensional list of colours.

I repeat: I cannot use any Python modules.

NOTE: I can switch to another video format, my goal is just to extract the frames using no modules. It's better to have a small video format.

I'm thinking about transcribing this https://github.com/webmproject/libvpx/tree/main/vp9/decoder into Python but I wish for an easier solution...

I tried using cv2.VideoCapture and that's exactly what I want, but I have to use pure Python with no modules. Here is my code :

import cv2

video = cv2.VideoCapture(r'./video.mp4')

currentframe = 0
while(True): 
    ret,frame = video.read()

    if ret:
        # "frame" here is perfect

        currentframe += 1
    else: 
        break
video.release() 
cv2.destroyAllWindows()

This is probably not the best solution for every use case but for mine, I decided to go with that :

1. Read the video frame by frame with CV2 and export every "horizontal line" of every frame in a txt file
2. Then read it with the python script I need line by line

I'm optimising this, but that's the basic solution I ended up finding.