[FFmpeg-user] Public FFmpeg Docker images built with GitHub Actions

[Ryan Williams]

Just wanted to mention this in case it's helpful to anyone:
https://hub.docker.com/r/runsascoded/ffmpeg

These are Docker images I've built and published (from source releases as
well as a few misc Git commits) using GitHub Actions on a fork of the
GitHub FFmpeg mirror: https://github.com/runsascoded/FFmpeg#readme

If you have Docker installed, you can run ffmpeg without having to install
it, e.g.:

```
$ docker run runsascoded/ffmpeg -version
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
…
```

Other versions are also available, e.g.:
```
$ docker run runsascoded/ffmpeg:4.2.4 -version
ffmpeg version 4.2.4 Copyright (c) 2000-2020 the FFmpeg developers
…
```

At the moment I've published images for 4.3.1 (which is also
"latest"/default), 4.3, 4.2.4, and 4.1.6. The Dockerfile build commands I'm
using fail on 4.0.6 and 3.4.8, and I haven't looked much at fixing them.

It might be nice to publish images like this under ffmpeg/ffmpeg (I only
see a coverity-related image with one "latest" tag not obviously tied to
any specific release under https://hub.docker.com/u/ffmpeg currently). The
GitHub Action workflow I used here is in principle upstream-able
(`DOCKERHUB_USER` and `DOCKERHUB_TOKEN` "secrets" on the FFmpeg GitHub
repo, as well as the presence of the .github/workflows/ci.yml file and
docker/build.{sh,py} scripts, would cause GitHub to run on every commit and
publish images tagged with every Git commit SHA, branch name, and tag), but
seems incompatible with existing development/release workflows, so I assume
it's not in the cards. Certainly anyone is welcome to take what I've done
and upstream some or all of it.

In the meantime I'll keep an eye out for new releases and push tags to
trigger Docker image builds for them. The /issues page is also open on my
fork in case I miss one: https://github.com/runsascoded/FFmpeg/issues

Thanks, happy to hear others' thoughts on this.

-Ryan