I read that and I followed the instructions. Several times. Im not sure if it just me being dumb or if its just my computer.
Sorry, but it's probably the first.
I'll be kind and explain it to you once.
Extract the .7z file, run the .bat file inside it, restart Minecraft.
Then, select
MP4 - Default Rendering
from the
Encoding Preset dropdown before rendering,
EVEN IF YOU ALREADY HAVE IT SET TO THAT VALUE. This is important!If it doesn't work, enter the Path to the extracted
ffmpeg.exe
(not the
ffmpeg.7z
!) in the LEFT, not the RIGHT input field of the Command Line Settings.