fix aspect_ratio other than 16:9 issue

[germanzhu]

Motivation

Video is squished on using aspect ratios other than 1920x1080 or 16:9.

This PR attempts to address this issue.

Proposed changes

• config.py
• constants.py
• shaders.py

Test

Code:

from manimlib import *


class Video(Scene):
    
    def construct(self):
        s = Square()
        c = Circle()
        self.play(ShowCreation(s))
        self.play(Transform(s,c))

manimgl test.py -r 1080x1920 -wo

Result:

Video.mp4