Implement tests

[tiangolo]

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Issue Content

To be able to consider changes for this repo, it would need some tests that run on CI to verify everything keeps working.

Setting up testing is probably not very straightforward, as it needs to deal with video streams.

When I created this repo, I tested/confirmed manually with OBS streaming and VLC reading and playing the stream. But that is not automated, and as I am not actively using the image, it's not easy to run manual tests for each possible change proposal.

I imagine tests could involve ffmpeg commands, maybe pytest and Python to ensure some things, or maybe plain bash could work. But it would need confirming that a source can stream the RTMP video, this image transmits it, and it can be read again.

[Robert-litts]

@tiangolo Saw this issue opened up on my PR #97.

I've been thinking about this for a bit, and I think there are a few options to try:

1. ffprobe
2. rtmp_stat

Between the two above in a Github action workflow, plus some docker health checks, I think that would be on the right track toward ensuring any PRs maintain functionality.

Thoughts?