code: def _unkown_type(self, uridecodebin, decodebin, caps):
          
          # This is called *before* the stream becomes ready when the
          # file can't be read.
          streaminfo = caps.to_string()
          if not streaminfo.startswith('audio/'):
              # Ignore non-audio (e.g., video) decode errors.
              return
          self.read_exc = UnknownTypeError(streaminfo)
          self.ready_sem.release()
docs: The callback for decodebin's "unknown-type" signal.