STT Metrics | LiveKit docs

This example shows how to log speech-to-text metrics (including end-of-utterance timings) every time the STT pipeline runs. The agent streams audio, and the STT plugin publishes metrics you render as Rich tables.

Prerequisites

Add a .env in this directory with your LiveKit credentials:

LIVEKIT_URL=your_livekit_url
LIVEKIT_API_KEY=your_api_key
LIVEKIT_API_SECRET=your_api_secret

Install dependencies:

pip install python-dotenv rich "livekit-agents[silero]"

Load configuration and logging

Set up dotenv, a logger, and a Rich console for reporting.

import logging
import asyncio
from dotenv import load_dotenv
from livekit.agents import JobContext, JobProcess, Agent, AgentSession, inference, AgentServer, cli
from livekit.agents.metrics import STTMetrics, EOUMetrics
from livekit.plugins import silero
from rich.console import Console
from rich.table import Table
from rich import box
from datetime import datetime

load_dotenv()

logger = logging.getLogger("metrics-stt")
logger.setLevel(logging.INFO)

console = Console()

server = AgentServer()

Prewarm VAD for faster connections

Preload the VAD model once per process to reduce connection latency.

def prewarm(proc: JobProcess):
    proc.userdata["vad"] = silero.VAD.load()

server.setup_fnc = prewarm

Keep the agent lightweight. In on_enter, attach two listeners: one for STT metrics and one for end-of-utterance (EOU) metrics. Wrap the handlers so you can await inside them.

class STTMetricsAgent(Agent):
    def __init__(self) -> None:
        super().__init__(
            instructions="""
                You are a helpful agent.
            """
        )

    async def on_enter(self):
        def stt_wrapper(metrics: STTMetrics):
            asyncio.create_task(self.on_stt_metrics_collected(metrics))

        def eou_wrapper(metrics: EOUMetrics):
            asyncio.create_task(self.on_eou_metrics_collected(metrics))

        self.session.stt.on("metrics_collected", stt_wrapper)
        self.session.stt.on("eou_metrics_collected", eou_wrapper)
        self.session.generate_reply()

Display STT stats

Each handler renders a Rich table. STT metrics include duration, speech ID, and audio duration.

async def on_stt_metrics_collected(self, metrics: STTMetrics) -> None:
        table = Table(
            title="[bold blue]STT Metrics Report[/bold blue]",
            box=box.ROUNDED,
            highlight=True,
            show_header=True,
            header_style="bold cyan"
        )

        table.add_column("Metric", style="bold green")
        table.add_column("Value", style="yellow")

        timestamp = datetime.fromtimestamp(metrics.timestamp).strftime('%Y-%m-%d %H:%M:%S')

        table.add_row("Type", str(metrics.type))
        table.add_row("Label", str(metrics.label))
        table.add_row("Request ID", str(metrics.request_id))
        table.add_row("Timestamp", timestamp)
        table.add_row("Duration", f"[white]{metrics.duration:.4f}[/white]s")
        table.add_row("Speech ID", str(metrics.speech_id))
        table.add_row("Error", str(metrics.error))
        table.add_row("Streamed", "✓" if metrics.streamed else "✗")
        table.add_row("Audio Duration", f"[white]{metrics.audio_duration:.4f}[/white]s")

        console.print("\n")
        console.print(table)
        console.print("\n")

Display EOU stats

EOU metrics include delays for detecting the end of an utterance and transcription delays.

async def on_eou_metrics_collected(self, metrics: EOUMetrics) -> None:
        table = Table(
            title="[bold blue]End of Utterance Metrics Report[/bold blue]",
            box=box.ROUNDED,
            highlight=True,
            show_header=True,
            header_style="bold cyan"
        )

        table.add_column("Metric", style="bold green")
        table.add_column("Value", style="yellow")

        timestamp = datetime.fromtimestamp(metrics.timestamp).strftime('%Y-%m-%d %H:%M:%S')

        table.add_row("Type", str(metrics.type))
        table.add_row("Label", str(metrics.label))
        table.add_row("Timestamp", timestamp)
        table.add_row("End of Utterance Delay", f"[white]{metrics.end_of_utterance_delay:.4f}[/white]s")
        table.add_row("Transcription Delay", f"[white]{metrics.transcription_delay:.4f}[/white]s")
        table.add_row("Speech ID", str(metrics.speech_id))
        table.add_row("Error", str(metrics.error))

        console.print("\n")
        console.print(table)
        console.print("\n")

Set up the session

Configure the AgentSession with STT, LLM, TTS, and prewarmed VAD. The STT's metrics events will be captured by the listeners attached in on_enter.

@server.rtc_session()
async def entrypoint(ctx: JobContext):
    ctx.log_context_fields = {"room": ctx.room.name}

    session = AgentSession(
        stt=inference.STT(model="deepgram/nova-3-general"),
        llm=inference.LLM(model="openai/gpt-4.1-mini"),
        tts=inference.TTS(model="cartesia/sonic-3", voice="9626c31c-bec5-4cca-baa8-f8ba9e84c8bc"),
        vad=ctx.proc.userdata["vad"],
        preemptive_generation=True,
    )
    agent = STTMetricsAgent()

    await session.start(agent=agent, room=ctx.room)
    await ctx.connect()

Run the server

Start the agent server with the CLI.

if __name__ == "__main__":
    cli.run_app(server)

Run it

python metrics_stt.py console

How it works

The agent uses Deepgram streaming STT with Silero VAD.
STT emits metrics_collected per request and eou_metrics_collected when speech ends.
Async handlers format and print the data so you can watch latency and audio durations live.
Because handlers run in tasks, they do not block audio processing.

Full example

import logging
import asyncio
from dotenv import load_dotenv
from livekit.agents import JobContext, JobProcess, Agent, AgentSession, inference, AgentServer, cli
from livekit.agents.metrics import STTMetrics, EOUMetrics
from livekit.plugins import silero
from rich.console import Console
from rich.table import Table
from rich import box
from datetime import datetime

load_dotenv()

logger = logging.getLogger("metrics-stt")
logger.setLevel(logging.INFO)

console = Console()

class STTMetricsAgent(Agent):
    def __init__(self) -> None:
        super().__init__(
            instructions="""
                You are a helpful agent.
            """
        )

    async def on_enter(self):
        def stt_wrapper(metrics: STTMetrics):
            asyncio.create_task(self.on_stt_metrics_collected(metrics))

        def eou_wrapper(metrics: EOUMetrics):
            asyncio.create_task(self.on_eou_metrics_collected(metrics))

        self.session.stt.on("metrics_collected", stt_wrapper)
        self.session.stt.on("eou_metrics_collected", eou_wrapper)
        self.session.generate_reply()

    async def on_stt_metrics_collected(self, metrics: STTMetrics) -> None:
        table = Table(
            title="[bold blue]STT Metrics Report[/bold blue]",
            box=box.ROUNDED,
            highlight=True,
            show_header=True,
            header_style="bold cyan"
        )

        table.add_column("Metric", style="bold green")
        table.add_column("Value", style="yellow")

        timestamp = datetime.fromtimestamp(metrics.timestamp).strftime('%Y-%m-%d %H:%M:%S')

        table.add_row("Type", str(metrics.type))
        table.add_row("Label", str(metrics.label))
        table.add_row("Request ID", str(metrics.request_id))
        table.add_row("Timestamp", timestamp)
        table.add_row("Duration", f"[white]{metrics.duration:.4f}[/white]s")
        table.add_row("Speech ID", str(metrics.speech_id))
        table.add_row("Error", str(metrics.error))
        table.add_row("Streamed", "✓" if metrics.streamed else "✗")
        table.add_row("Audio Duration", f"[white]{metrics.audio_duration:.4f}[/white]s")

        console.print("\n")
        console.print(table)
        console.print("\n")

    async def on_eou_metrics_collected(self, metrics: EOUMetrics) -> None:
        table = Table(
            title="[bold blue]End of Utterance Metrics Report[/bold blue]",
            box=box.ROUNDED,
            highlight=True,
            show_header=True,
            header_style="bold cyan"
        )

        table.add_column("Metric", style="bold green")
        table.add_column("Value", style="yellow")

        timestamp = datetime.fromtimestamp(metrics.timestamp).strftime('%Y-%m-%d %H:%M:%S')

        table.add_row("Type", str(metrics.type))
        table.add_row("Label", str(metrics.label))
        table.add_row("Timestamp", timestamp)
        table.add_row("End of Utterance Delay", f"[white]{metrics.end_of_utterance_delay:.4f}[/white]s")
        table.add_row("Transcription Delay", f"[white]{metrics.transcription_delay:.4f}[/white]s")
        table.add_row("Speech ID", str(metrics.speech_id))
        table.add_row("Error", str(metrics.error))

        console.print("\n")
        console.print(table)
        console.print("\n")

server = AgentServer()

def prewarm(proc: JobProcess):
    proc.userdata["vad"] = silero.VAD.load()

server.setup_fnc = prewarm

@server.rtc_session()
async def entrypoint(ctx: JobContext):
    ctx.log_context_fields = {"room": ctx.room.name}

    session = AgentSession(
        stt=inference.STT(model="deepgram/nova-3-general"),
        llm=inference.LLM(model="openai/gpt-4.1-mini"),
        tts=inference.TTS(model="cartesia/sonic-3", voice="9626c31c-bec5-4cca-baa8-f8ba9e84c8bc"),
        vad=ctx.proc.userdata["vad"],
        preemptive_generation=True,
    )
    agent = STTMetricsAgent()

    await session.start(agent=agent, room=ctx.room)
    await ctx.connect()

if __name__ == "__main__":
    cli.run_app(server)