Metrics not emitting for STT Elevenlabs LiveKit Community #ask-ai

Join Slack

Metrics not emitting for STT - Elevenlabs

# ask-ai

boundless-battery-65494

08/19/2025, 6:46 AM

Metrics not emitting for STT - Elevenlabs

tall-airline-16756

08/19/2025, 6:46 AM

Thanks for reaching out, MOHAN. I'm an AI assistant and I'm here to help. Give me a moment while I research this topic.

tall-airline-16756

08/19/2025, 6:46 AM

Hey there! Just a quick heads-up about the ElevenLabs STT integration in LiveKit — it doesn’t emit

RECOGNITION_USAGE

events. These events are important because they trigger the

STTMetrics

in the streaming metrics monitor task. The reason behind this is that ElevenLabs STT handles the whole audio buffer with a non-streaming HTTP request and only sends back a

FINAL_TRANSCRIPT

event once it’s done processing. Because

RECOGNITION_USAGE

events aren’t generated during this process, the

_metrics_monitor_task

inside the

RecognizeStream

class won’t emit

STTMetrics

for streaming sessions. But don’t worry — the

recognize()

method still sends out metrics for non-streaming requests. If you’re working with ElevenLabs STT in streaming mode, this is totally expected behavior. Metrics collection works a bit differently between streaming and non-streaming modes. If you want me to walk you through it or if you have any other questions, just let me know — I’m here to help! Sources: README.md | livekit-plugins/livekit-plugins-elevenlabs/livekit/plugins/elevenlabs/tts.p... | Capturing metrics | LiveKit Docs

boundless-battery-65494

08/19/2025, 6:52 AM

agentTts.on(tts.TTSEvent.METRICS_COLLECTED, (agentMetrics) => { console.log(agentMetrics); if (agentMetrics.ttfb) { // Record the TTS TTFB. turnMetrics.ttsTTFB = agentMetrics.ttfb; } } I am using metrics collected this event is not triggered by elevenlabs. I dont know ? but its working good with cartesia

tall-airline-16756

08/19/2025, 6:53 AM

Hey there! To help figure out why the

TTSEvent.METRICS_COLLECTED

event isn’t showing up for ElevenLabs, could you please check a few things for me? • Are you using streaming or chunked synthesis with ElevenLabs? • After pushing text, are you calling

flush()

and

end_input()

on the ElevenLabs TTS stream? • Which versions of

livekit-agents

and

livekit-plugins-elevenlabs

are you working with? Getting these details will really help us understand whether it’s a usage thing, a setup issue, or maybe even a bug. Thanks so much for checking! Sources: livekit-agents/livekit/agents/tts/tts.py | agents/src/tts/stream_adapter.ts | TTSEvent | LiveKit Agents

boundless-battery-65494

08/19/2025, 6:58 AM

• Are you using streaming or chunked synthesis with ElevenLabs? - NO • After pushing text, are you calling

flush()

and

end_input()

on the ElevenLabs TTS stream? - NO • Which versions of

livekit-agents

and

livekit-plugins-elevenlabs

are you working with? - 0.7.9

tall-airline-16756

08/19/2025, 6:58 AM

Hey there! Just a quick heads-up: the

TTSEvent.METRICS_COLLECTED

event is supported in

livekit-plugins-elevenlabs

version 0.7.9. But since you’re not using streaming synthesis and haven’t called

flush()

end_input()

, the metrics event might not show up like you’d expect. To get this working smoothly, make sure the text is properly sent to the ElevenLabs TTS stream, and that you flush and end the stream correctly. These little steps help the metrics collection finish up and trigger the event. If you want, I’m here to help you walk through these steps—just let me know! Sources: agents/CHANGELOG.md

boundless-battery-65494

08/19/2025, 6:59 AM

can you share the code snippets. it will help me to resolve. Note: My stack is node.js not python

tall-airline-16756

08/19/2025, 7:00 AM

Here are some Node.js code snippets to help you easily collect TTS metrics using

TTSEvent.METRICS_COLLECTED

with ElevenLabs. I’ve got your back! Basic Metrics Collection:

Copy code

import { TTSEvent } from '@livekit/agents';
import { TTS } from '@livekit/plugins-elevenlabs'; // ElevenLabs TTS plugin

// Create ElevenLabs TTS instance
const tts = new TTS();

// Listen for metrics collection events
tts.on(TTSEvent.METRICS_COLLECTED, (metrics) => {
  console.log('TTS Metrics:', {
    timestamp: metrics.timestamp,
    requestId: metrics.requestId,
    ttfb: metrics.ttfb, // Time to first byte in milliseconds
    duration: metrics.duration, // Total duration in milliseconds
    charactersCount: metrics.charactersCount,
    audioDuration: metrics.audioDuration, // Audio duration in seconds
    cancelled: metrics.cancelled,
    label: metrics.label,
    streamed: metrics.streamed
  });
});

Advanced Metrics Processing:

Copy code

import { TTSEvent } from '@livekit/agents';
import { TTS } from '@livekit/plugins-elevenlabs';

class TTSMetricsCollector {
  constructor() {
    this.metrics = [];
  }

  setupTTS() {
    const tts = new TTS();
    
    tts.on(TTSEvent.METRICS_COLLECTED, (metrics) => {
      this.collectMetrics(metrics);
    });
    
    return tts;
  }

  collectMetrics(metrics) {
    // Store metrics for analysis
    this.metrics.push({
      ...metrics,
      timestamp: new Date(metrics.timestamp).toISOString()
    });

    // Log key performance indicators
    console.log(`TTS Performance - TTFB: ${metrics.ttfb}ms, Duration: ${metrics.duration}ms, Characters: ${metrics.charactersCount}`);
    
    // Calculate efficiency ratio
    const efficiency = metrics.audioDuration / (metrics.duration / 1000);
    console.log(`Audio efficiency: ${efficiency.toFixed(2)}x realtime`);
  }

  getAverageMetrics() {
    if (this.metrics.length === 0) return null;
    
    const totals = this.metrics.reduce((acc, metric) => ({
      ttfb: acc.ttfb + metric.ttfb,
      duration: acc.duration + metric.duration,
      charactersCount: acc.charactersCount + metric.charactersCount,
      audioDuration: acc.audioDuration + metric.audioDuration
    }), { ttfb: 0, duration: 0, charactersCount: 0, audioDuration: 0 });

    const count = this.metrics.length;
    return {
      avgTTFB: totals.ttfb / count,
      avgDuration: totals.duration / count,
      avgCharacters: totals.charactersCount / count,
      avgAudioDuration: totals.audioDuration / count
    };
  }
}

// Usage
const collector = new TTSMetricsCollector();
const tts = collector.setupTTS();

If you have any questions or want help integrating these snippets into your app, just let me know—I’m here to help! Sources: Capturing metrics | LiveKit Docs | agents/src/pipeline/pipeline_agent.ts

boundless-battery-65494

08/19/2025, 7:02 AM

NO. I am using pipeline.voicePipelineAgent. const agent = new pipeline.VoicePipelineAgent( ... llm, stt,vad tts = new elevenlabs.TTS() );

tall-airline-16756

08/19/2025, 7:02 AM

To collect TTS metrics using

VoicePipelineAgent

with ElevenLabs TTS, you can simply listen for the

VPAEvent.METRICS_COLLECTED

event. Here’s a handy Node.js code snippet to get you started:

Copy code

import { VoicePipelineAgent, VPAEvent } from '@livekit/agents';
import { TTS } from '@livekit/agents-plugin-elevenlabs';

const agent = new VoicePipelineAgent(vad, stt, llm, tts);

// Listen for all metrics including TTS metrics
agent.on(VPAEvent.METRICS_COLLECTED, (metrics) => {
  if (metrics.label === 'elevenlabs.TTS') {
    console.log('ElevenLabs TTS Metrics:', {
      duration: metrics.duration,
      charactersCount: metrics.charactersCount,
      audioDuration: metrics.audioDuration,
      ttfb: metrics.ttfb,
      sequenceId: metrics.sequenceId
    });
  }
});

The

VPAEvent.METRICS_COLLECTED

event gives you useful info like

duration

charactersCount

audioDuration

, and

ttfb

. These come straight from the ElevenLabs TTS plugin as it works its magic during synthesis. If you have any questions or want to dive deeper into this, just let me know—I’m here to help! Sources: agents/src/tts/tts.ts | PipelineTTSMetrics | LiveKit Agents

boundless-battery-65494

08/19/2025, 7:04 AM

agentTts.on(tts.TTSEvent.METRICS_COLLECTED, (agentMetrics) => { console.log(agentMetrics); if (agentMetrics.ttfb) { // Record the TTS TTFB. turnMetrics.ttsTTFB = agentMetrics.ttfb; } } why this event is not working with elevenlabs but works with cartesia

tall-airline-16756

08/19/2025, 7:05 AM

Hey there! To help figure out why

TTSEvent.METRICS_COLLECTED

isn't triggering for ElevenLabs but works fine with Cartesia, could you share a bit more info? • Do you see any error logs or messages in the console when using ElevenLabs? • Is ElevenLabs successfully producing audio output when you try it? • Which versions of the ElevenLabs and Cartesia plugins are you working with? • How are you currently listening for the

TTSEvent.METRICS_COLLECTED

event in your code? With these details, we’ll be in a much better spot to pinpoint if it’s something with the setup or maybe a small difference in how it’s implemented. Looking forward to helping you get this sorted! Sources: livekit-plugins/livekit-plugins-elevenlabs/livekit/plugins/elevenlabs/tts.p... | agents/src/pipeline/pipeline_agent.ts

Open in Slack

Previous Next