I had a go at implementing https://github.com/timvideos/gst-switch/issues/194. This branch adds the Avahi client libraries as a dependency, but the resulting binaries should still run if the Avahi service isn't running (it will just fail to publish the service).

It publishes two services of the types _gstswitch-video._tcp and _gstswitch-audio._tcp that match the two listening ports. Each service has two TXT records attached:

• txtvers - a version number for the TXT metadata, in case it ever needs to be changed incompatibly.
• caps - the string version of the GstCaps expected for data sent to this port.

This should be enough for a smart capture client to notice when the server appears on the network, and what format data to send. It could also automatically reconnect if the server changes IP address.

By default the server will use the name gst-switch, but this can be changed using the --service-name command line option. If there are name conflicts, it will use Avahi's standard name conflict resolution method.

The code is based on the example from the Avahi documentation:

http://git.0pointer.net/avahi.git/tree/examples/client-publish-service.c

As an example, here is the avahi-browse output watching the audio service when I start and kill the server:

$ avahi-browse -r _gstswitch-audio._tcp
+   eth0 IPv6 gst-switch                                    _gstswitch-audio._tcp local
+   eth0 IPv4 gst-switch                                    _gstswitch-audio._tcp local
=   eth0 IPv6 gst-switch                                    _gstswitch-audio._tcp local
   hostname = [scruffy.local]
   address = [fe80::6ef0:49ff:feed:eadd]
   port = [4000]
   txt = ["caps=audio/x-raw, rate=48000, channels=2, format=S16LE, layout=interleaved" "txtvers=1"]
=   eth0 IPv4 gst-switch                                    _gstswitch-audio._tcp local
   hostname = [scruffy.local]
   address = [192.168.0.12]
   port = [4000]
   txt = ["caps=audio/x-raw, rate=48000, channels=2, format=S16LE, layout=interleaved" "txtvers=1"]
-   eth0 IPv6 gst-switch                                    _gstswitch-audio._tcp local
-   eth0 IPv4 gst-switch                                    _gstswitch-audio._tcp local