[PLUG-AV] Another experiment in updating our AV workflow

[James Henstridge]

As an evening project, I've been having another go at trying to
modernise PLUG's recording/streaming workflow.  I think I've got
enough working to demonstrate some of it at tonight's PLUG meeting,
but thought I'd outline some of the details here.

Benjamin had mentioned OBS Studio as a possible way forward, so that's
what I used as my starting point.  The main thing it's missing from
our old dvswitch based workflow was an easy way to integrate remote
cameras into the scene, so that's what I've been focusing on.  The
work in progress code can be found in this repo:

https://github.com/jhenstridge/obs-rtsp-source

It comprises two pieces:

1. an RTSP server to share a camera stream over the network
2. an OBS plugin that helps configure OBS Studio's standard "Media
Source" to consume these streams.

The RTSP server advertises each stream via Zeroconf using Avahi, so
you can see all the cameras available on the network with
"avahi-browse -rt _rtsp._tcp".  I'm still working on adding the Avahi
support to the OBS plugin so it can select cameras by published name
rather than an rtsp:// URI.

The eventual goal is to allow the different parts to self configure.
If you turn the camera nodes on first, then the OBS machine should
connect to them when it starts.  If the OBS machine starts first, it
will wait until the cameras come online, and plug them into the scenes
you've set up previously.  If everything works correctly, then the
RTSP sender machines could easily be headless: the RTSP server would
start on boot, and Avahi would advertise the camera once it gets a
DHCP address.

Given that tonight is our Raspberry Pi Jam, I thought I'd put this to
the test, and have configured a Pi running the RTSP software.  So
hopefully we can give this a short demonstration.

James.