This is the base for https://hub.docker.com/r/corprew/spackle-base/.
It adds ruby to https://hub.docker.com/r/corprew/ffmpeg-nonfree-docker/.
It is useful as a base for images that use ruby to participate in media processing frameworks.
You could also do this by adding ffmpeg to the official ruby images from docker, but that's alpine linux, so if you have some unknown ubuntu dependency, you should use this instead.