Prerequisite: Having vapoursynth installed

Installed vapoursynth-wwxd

1. Download or clone https://github.com/dubhater/vapoursynth-wwxd
2. gcc -o libwwxd.so -fPIC -shared -O2 -Wall -Wextra -Wno-unused-parameter $(pkg-config --cflags vapoursynth) src/wwxd.c src/detection.c in the folder
3. Move the file libwwxd.so in /usr/lib/vapoursynth/ and change ownership to root (sudo chown root:root libwwxd.so)

Launch the generate_keyframes.py script

1. Save https://raw.githubusercontent.com/LightArrowsEXE/fansub-utils/master/generate_keyframes.py in a folder to the name generate_keyframes.py
2. python3 generate_keyframes.py --f 'Your_file.mp4'
3. Import them in aegisub using Videos > Open Keyframes