def on_message(self, bus, message):
        t = message.type
        if t == gst.MESSAGE_ERROR:
            err, debug = message.parse_error()
            print "Error: %s" % err, debug
            if self.on_eos:
                self.on_eos()
            self.playing = False
        elif t == gst.MESSAGE_EOS:
            if self.on_eos:
                self.on_eos()
            self.playing = False


    def setup(self):
        ...
        bus = pipeline.get_bus()
        bus.add_signal_watch()
        bus.connect('message', self.on_message)
        ...