code: def _pad_added(self, element, pad):
          
          # Decoded data is ready. Connect up the decoder, finally.
          name = pad.query_caps(None).to_string()
          if name.startswith('audio/x-raw'):
              nextpad = self.conv.get_static_pad('sink')
              if not nextpad.is_linked():
                  self._got_a_pad = True
                  pad.link(nextpad)
docs: The callback for GstElement's "pad-added" signal.