Intercepting Bus messages in gstreamer plugin - plugins

Question

I'm writing a gstreamer plugin that uses a uridecodebin. I'd like to be able to intercept the error that occurs when the uridecodebin is unable to open a file (either because of a malformed URI, an unknown file format, or a non-existent file) before it's reported to the application using the pipeline. When I try to add a watch to the uridecodebin's bus myself, it fails (gst_bus_create_watch: assertion bus->priv->poll != NULL) and I get a segfault.
How can I intercept the error before it's reported to the application so that I can gracefully fail internally? It isn't a critical error for the plugin as a whole if the file isn't loaded, and I'd like to be able to do some cleanup work when that happens.

Answer 1

You need to read this page:
http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/chapter-bus.html
Using wxpython, I do the following:
# Create the bus to listen for messages
bus = Gplayer.get_bus()
bus.add_signal_watch()
bus.enable_sync_message_emission()
bus.connect('message', self.OnBusMessage)
# Listen for gstreamer bus messages
def OnBusMessage(self, bus, message):
t = message.type
if t == Gst.MessageType.ERROR:
Gplayer.set_state(Gst.State.NULL)
self.OnStop(None)
wx.MessageBox('Gstreamer Error - Unsupported file type, Corrupt file,\
Unable to access or Invalid Output Device', 'Error', wx.OK | wx.ICON_INFORMATION)
Or in your case, don't report anything.
EDIT:
You can parse the message to see part 1 which will be the error and part 2 which will be a more verbose explanation.
# Listen for gstreamer bus messages
def OnBusMessage(self, bus, message):
t = message.type
if t == Gst.MessageType.ERROR:
print "Part 1",Gst.Message.parse_error (message)[0]
print "part 2",Gst.Message.parse_error (message)[1]
This is what I get from the above for a missing file:
Part 1 Not Found
part 2 gstsouphttpsrc.c(1192): gst_soup_http_src_parse_status (): /GstPlayBin:playbin/GstURIDecodeBin:uridecodebin0/GstSoupHTTPSrc:source:
Not Found (404), URL: http://localhost/vvvv.mp3
Note: This assumes that you will add code to the existing watch
Edit 2:
With regard to your second comment, have you investigated gst_bus_new().
It appears at first glance, that it may help you.