Bug report

Bug summary
When I use the animation.writers['ffmpeg'] in my python3 code and execute it in background on Ubuntu, the process is hung forever.

Code for reproduction
My chk.py python code contains these 3 lines below.

import matplotlib.pyplot as plt
import matplotlib.animation as animation
Writer = animation.writers['ffmpeg']

I run the above code as python3 chk.py & and it is hung forever.

Matplotlib version

• Operating system: Ubuntu 18.04 LTS
• Matplotlib version: 3.2.2
• Matplotlib backend (print(matplotlib.get_backend())): GTK3Agg
• Python version: 3.6.9
• Jupyter version (if applicable): NA
• Other libraries:

Instlaled matplotlin using pip3