WebSocket API

import WebSocket from "ws";

const agentId = process.env.CARTESIA_AGENT_ID;
const apiKey = process.env.CARTESIA_API_KEY;

if (!agentId || !apiKey) {
  throw new Error("Set CARTESIA_AGENT_ID and CARTESIA_API_KEY");
}

const ws = new WebSocket(
  `wss://api.cartesia.ai/v1/agents/websocket/${agentId}` +
    "?cartesia_version=2026-08-14",
  { headers: { "X-API-Key": apiKey } }
);

let ready = false;
let callId;

ws.on("open", () => {
  ws.send(JSON.stringify({
    type: "session_create",
    audio: {
      input_format: "pcm_44100",
      output_delivery: "speaking_pace",
    },
  }));
});

ws.on("message", (data) => {
  const event = JSON.parse(data.toString());

  if (event.type === "session_ready") {
    ready = true;
    // Save this ID to retrieve the call record, transcript, or audio later.
    callId = event.call_id;
    console.log("Session ready:", callId);
  }
  if (event.type === "audio_output") playAudio(decodeAudio(event.audio));
  if (event.type === "audio_output_clear") stopPlayback();
});

function sendAudio(audioBytes) {
  if (!ready) return;
  // With pcm_44100, pass headerless mono signed 16-bit little-endian PCM bytes.
  // Base64-encode each 20–100 ms audio input chunk for its JSON text event.
  // Short chunks let Cartesia begin processing speech sooner and reduce response latency.
  const base64Audio = Buffer.from(audioBytes).toString("base64");
  ws.send(JSON.stringify({ type: "audio_input", audio: base64Audio }));
}

function decodeAudio(base64Audio) {
  return Buffer.from(base64Audio, "base64");
}

function playAudio(audioBytes) {
  console.log("Received agent audio bytes:", audioBytes.byteLength);
}

function stopPlayback() {
  console.log("Received audio_output_clear");
}

ws.on("close", (code, reason) => console.log("Closed:", code, String(reason)));
ws.on("error", console.error);