Text-to-Speech (HeyGen Starfish)

Generate speech audio files from text using HeyGen's in-house Starfish TTS model. This skill is for standalone audio generation — separate from video creation.

Authentication

All requests require the X-Api-Key header. Set the HEYGEN_API_KEY environment variable.

curl -X GET "https://api.heygen.com/v1/audio/voices" \
  -H "X-Api-Key: $HEYGEN_API_KEY"

Tool Selection

If HeyGen MCP tools are available (mcp__heygen__*), prefer them over direct HTTP API calls.

Default Workflow

1. List voices with mcp__heygen__list_audio_voices (or GET /v1/audio/voices)
2. Pick a voice matching desired language, gender, and features
3. Call mcp__heygen__text_to_speech (or POST /v1/audio/text_to_speech) with text and voice_id
4. Use the returned audio_url to download or play the audio

List TTS Voices

Retrieve voices compatible with the Starfish TTS model.

Note: This uses GET /v1/audio/voices — a different endpoint from the video voices API (GET /v2/voices). Not all video voices support Starfish TTS.

curl

curl -X GET "https://api.heygen.com/v1/audio/voices" \
  -H "X-Api-Key: $HEYGEN_API_KEY"

TypeScript

interface TTSVoice {
  voice_id: string;
  language: string;
  gender: "female" | "male" | "unknown";
  name: string;
  preview_audio_url: string | null;
  support_pause: boolean;
  support_locale: boolean;
  type: string;
}

interface TTSVoicesResponse {
  error: null | string;
  data: {
    voices: TTSVoice[];
  };
}

async function listTTSVoices(): Promise<TTSVoice[]> {
  const response = await fetch("https://api.heygen.com/v1/audio/voices", {
    headers: { "X-Api-Key": process.env.HEYGEN_API_KEY! },
  });

  const json: TTSVoicesResponse = await response.json();

  if (json.error) {
    throw new Error(json.error);
  }

  return json.data.voices;
}

Python

import requests
import os

def list_tts_voices() -> list:
    response = requests.get(
        "https://api.heygen.com/v1/audio/voices",
        headers={"X-Api-Key": os.environ["HEYGEN_API_KEY"]}
    )

    data = response.json()
    if data.get("error"):
        raise Exception(data["error"])

    return data["data"]["voices"]

Response Format

{
  "error": null,
  "data": {
    "voices": [
      {
        "voice_id": "f38a635bee7a4d1f9b0a654a31d050d2",
        "name": "Chill Brian",
        "language": "English",
        "gender": "male",
        "preview_audio_url": "https://resource.heygen.ai/text_to_speech/WpSDQvmLGXEqXZVZQiVeg6.mp3",
        "support_pause": true,
        "support_locale": false,
        "type": "public"
      }
    ]
  }
}

Generate Speech Audio

Convert text to speech audio using a specified voice.

Endpoint

POST https://api.heygen.com/v1/audio/text_to_speech

Request Fields

ElevenLabs Settings (optional)

curl

curl -X POST "https://api.heygen.com/v1/audio/text_to_speech" \
  -H "X-Api-Key: $HEYGEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "text": "Hello! Welcome to our product demo.",
    "voice_id": "YOUR_VOICE_ID",
    "speed": 1.0
  }'

TypeScript

interface TTSRequest {
  text: string;
  voice_id: string;
  speed?: number;
  pitch?: number;
  locale?: string;
  elevenlabs_settings?: {
    model?: string;
    similarity_boost?: number;
    stability?: number;
    style?: number;
  };
}

interface WordTimestamp {
  word: string;
  start: number;
  end: number;
}

interface TTSResponse {
  error: null | string;
  data: {
    audio_url: string;
    duration: number;
    request_id: string;
    word_timestamps: WordTimestamp[];
  };
}

async function textToSpeech(request: TTSRequest): Promise<TTSResponse["data"]> {
  const response = await fetch(
    "https://api.heygen.com/v1/audio/text_to_speech",
    {
      method: "POST",
      headers: {
        "X-Api-Key": process.env.HEYGEN_API_KEY!,
        "Content-Type": "application/json",
      },
      body: JSON.stringify(request),
    }
  );

  const json: TTSResponse = await response.json();

  if (json.error) {
    throw new Error(json.error);
  }

  return json.data;
}

Python

import requests
import os

def text_to_speech(
    text: str,
    voice_id: str,
    speed: float = 1.0,
    pitch: int = 0,
    locale: str | None = None,
) -> dict:
    payload = {
        "text": text,
        "voice_id": voice_id,
        "speed": speed,
        "pitch": pitch,
    }

    if locale:
        payload["locale"] = locale

    response = requests.post(
        "https://api.heygen.com/v1/audio/text_to_speech",
        headers={
            "X-Api-Key": os.environ["HEYGEN_API_KEY"],
            "Content-Type": "application/json",
        },
        json=payload,
    )

    data = response.json()
    if data.get("error"):
        raise Exception(data["error"])

    return data["data"]

Response Format

{
  "error": null,
  "data": {
    "audio_url": "https://resource2.heygen.ai/text_to_speech/.../id=365d46bb.wav",
    "duration": 5.526,
    "request_id": "p38QJ52hfgNlsYKZZmd9",
    "word_timestamps": [
      { "word": "<start>", "start": 0.0, "end": 0.0 },
      { "word": "Hey", "start": 0.079, "end": 0.219 },
      { "word": "there,", "start": 0.239, "end": 0.459 },
      { "word": "<end>", "start": 5.526, "end": 5.526 }
    ]
  }
}

Usage Examples

Basic TTS

const result = await textToSpeech({
  text: "Welcome to our quarterly earnings call.",
  voice_id: "YOUR_VOICE_ID",
});

console.log(`Audio URL: ${result.audio_url}`);
console.log(`Duration: ${result.duration}s`);

With Speed Adjustment

const result = await textToSpeech({
  text: "We're thrilled to announce our newest feature!",
  voice_id: "YOUR_VOICE_ID",
  speed: 1.1,
});

With Locale for Multilingual Voices

const result = await textToSpeech({
  text: "Bem-vindo ao nosso produto.",
  voice_id: "MULTILINGUAL_VOICE_ID",
  locale: "pt-BR",
});

Find a Voice and Generate Audio

async function generateSpeech(text: string, language: string): Promise<string> {
  const voices = await listTTSVoices();
  const voice = voices.find(
    (v) => v.language.toLowerCase().includes(language.toLowerCase())
  );

  if (!voice) {
    throw new Error(`No TTS voice found for language: ${language}`);
  }

  const result = await textToSpeech({
    text,
    voice_id: voice.voice_id,
  });

  return result.audio_url;
}

const audioUrl = await generateSpeech("Hello and welcome!", "english");

Pauses with Break Tags

Use SSML-style break tags in your text for pauses:

word <break time="1s"/> word

Rules:

• Use seconds with s suffix: <break time="1.5s"/>
• Must have spaces before and after the tag
• Self-closing tag format

Expressive Voice Direction

For narration, create a short voice-performance plan before generating audio:

• narrator persona and emotional intent
• pacing profile
• energy curve across the script
• where pauses should land
• words or phrases that need emphasis

Use concrete cues, not generic instructions. "Warm but decisive; pause before the contrast; slow down on the final sentence" is useful. "Sound natural" is not.

When the selected voice supports pauses, put the most important pauses directly in the text with break tags. Generate a sample from the most performance-heavy section first, and do not batch-generate the rest if the sample sounds flat, rushed, or ignores the intended breaks.

Best Practices

1. Use GET /v1/audio/voices to find compatible voices — not all voices from GET /v2/voices support Starfish TTS
2. Check support_locale before setting a locale — only multilingual voices support locale selection
3. Keep speed between 0.8-1.2 for natural-sounding output
4. Preview voices using the preview_audio_url before generating (may be null for some voices)
5. Use word_timestamps in the response for caption syncing or timed text overlays
6. Use SSML break tags in your text for pauses: word <break time="1s"/> word