camera-sample-custom fails on Ubuntu

[hamishwillee]

1. The intro text is confusing:
   • "This sample demonstrates how to extend CSD by adding extra streams." - I think this is saying that it adds a new "dummy" stream and publishes it. How is this useful? ie what would be a real world application that would use this knowledge?
   • "This sample exports all streams exported by CSD and one extra stream with a dummy video generated by the videotestsrc gstreamer plugin."
     I think this is saying that the example adds an additional stream - basically it is CSD + an extra stream. Is that correct? My confusion is how this "works" - ie if the example does everything then I don't see how this extends CSD. It is somehow that this example builds a plugin for normal CSD and then calls CSD?. Does that make sense?
2. Are there any special requirements on the config for this to work? ie does it need to specify a particular mavlink port etc?
3. Example starts, but there are issues (as shown below). The log stops where shown below and waits. No video is displayed (as documented).

$ ./samples/camera-sample-custom -c samples/files/ubuntu.conf
CAMERA SERVER START
MAVLINK START

Open UDP [5]

(camera-sample-custom:6891): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Unable to start rtsp server
AVAHI START