There are many references to this error (or something close to it) in google, but it's not at all clear to me where it originates:
With rygel/gupnp-tools when attempting to view a streamed video: (rygel:8566): GLib-CRITICAL **: g_once_init_leave: assertion `result != 0' failed
..and something very similar happens when playing streamed music with rhythmbox, in both cases the application hangs. This didn't used to happen, but I'm not sure which of the glib/gtk/gstreamer/ffmpeg extensions causes it.
Does anybody have an idea where the fix might lie?