def _get_writer(self, i):
        """
        Returns a tuple of (log_fn, log_f, bin_fn, bin_f) to be written to by vectorized env channel i
        Or all Nones if recording is inactive on that channel
        """
        if self._recording_dir is None:
            return None
        if self._log_n is None:
            self._log_n = [None] * self.n
        if self._log_n[i] is None:
            self._log_n[i] = RecordingWriter(self._recording_dir, self._instance_id, i, async_write=self._async_write)
        return self._log_n[i]