Hide subprocess output and store it in a variable in Python

Question

I would like to call a FFmpeg command, which produces a very big output.

I need to store the output in order to make a regex on it.

On the first command (echo), nothing is printed in my terminal, but for the ffmpeg command, huge output is produced (which I want to store in a variable, I don't want to have the output in my terminal)

So my code looks like this for example:

import subprocess
output = subprocess.check_output("echo a lot of wooooords")
output = subprocess.check_output("ffmpeg -i audio.mp3 -f null -", shell=True)

Is it possible to hide the output for this command? Why does it show me an output? Thank you