WARNING this is not working.
Use the VLC RTSP server to stream a MP4 file.
As an alternative, you can use https://github.com/rgl/mediamtx-rtsp-server.
Install VLC:
# remove the debian/ubuntu package.
# NB it does not support RTSP due to live555 licensing concerns.
sudo apt-get remove -y --purge 'vlc*'
# install the snap package.
sudo snap install vnc
hash -r
Start the RTSP server:
./server.sh
In another shell, start the VLC RTSP client:
./client.sh