def ttfb(self) -> Optional[float]:
        """Get the current TTFB value in seconds.

        Returns:
            Optional[float]: The TTFB value in seconds, or None if not measured
        """
        if self._last_ttfb_time > 0:
            return self._last_ttfb_time

        # If TTFB is in progress, calculate current value
        if self._start_ttfb_time > 0:
            return time.time() - self._start_ttfb_time

        return None
Get the current TTFB value in seconds.

        Returns:
            Optional[float]: The TTFB value in seconds, or None if not measured
        
src/pipecat/processors/metrics/frame_processor_metrics.py