Gemini Text-to-Speech

Generate natural, expressive speech from text using Google Gemini TTS. Supports 70+ languages, 30 prebuilt voices, and style control via natural language prompts and audio tags.

Requirements: Node.js 18+, ffmpeg, @google/genai npm package, GEMINI_API_KEY env var.

Available Scripts

• scripts/generate-tts.mjs — All-in-one TTS generator with single-request consistency, silence-based splitting, and automatic trimming.

Quick Start

Single text to speech

npm install @google/genai
GEMINI_API_KEY=your-key node scripts/generate-tts.mjs \
  --text "Hello, welcome to our product!" \
  --output-dir public/vo \
  --voice Kore

Multi-segment voiceover (consistent voice)

Create a segments.json:

[
  { "id": "intro", "text": "Welcome to our product launch." },
  { "id": "features", "text": "Here are the three features you will love." },
  { "id": "close", "text": "Get started today at our website." }
]

Run:

GEMINI_API_KEY=your-key node scripts/generate-tts.mjs \
  --segments segments.json \
  --output-dir public/vo \
  --voice Kore \
  --director-notes "Tone: Warm, confident, inspiring. Style: Professional narrator with a vocal smile. Accent: Neutral American English. Pacing: Moderate."

Output (JSON to stdout):

{
  "success": true,
  "segments": [
    { "id": "intro", "file": "public/vo/vo-intro.mp3", "duration": 3.25 },
    { "id": "features", "file": "public/vo/vo-features.mp3", "duration": 4.10 },
    { "id": "close", "file": "public/vo/vo-close.mp3", "duration": 2.80 }
  ],
  "totalDuration": 10.15,
  "fullAudioFile": "public/vo/vo-full.wav"
}

Script Options

Flag	Default	Description
--segments FILE	—	JSON file with [{id, text}] segment definitions
--text TEXT	—	Single text to generate (alternative to --segments)
--output-dir DIR	—	Output directory for audio files (required)
--voice NAME	Kore	Prebuilt voice name (see Voices table)
--model NAME	gemini-3.1-flash-tts-preview	Gemini TTS model ID
--director-notes TEXT	—	Performance guidance: style, pacing, accent, breathing, articulation. Does not control gender/age (use --voice for that).
--retries N	3	Max retry attempts for API errors
--trim / --no-trim	--trim	Trim silence from segment boundaries
--format FORMAT	mp3	Output format: mp3 or wav

Exit Codes

Code	Meaning
0	Success
1	Missing required arguments or env vars
2	API error after retries exhausted
3	ffmpeg not installed or processing failed
4	File I/O error

How It Works (Multi-Segment)

Gemini TTS does NOT guarantee voice consistency across separate API requests. The script solves this by:

1. Combining all segments into ONE prompt with [3 second pause] markers between them
2. Generating a single continuous audio file in one API call
3. Detecting silence gaps with ffmpeg silencedetect using adaptive thresholds (starts at noise=-35dB, d=1.5s, progressively relaxes). If an exact match is found, uses it directly. If a threshold jump occurs (too few → too many), regenerates audio with faster speech pacing to make inter-segment pauses more distinct, then retries detection.
4. Splitting at silence midpoints into individual segment files
5. Trimming residual silence padding (~1.5s per side) from each segment, keeping 0.15s breathing room

Models

Model	Best For
gemini-3.1-flash-tts-preview	Latest, most controllable, 200+ audio tags (default)
gemini-2.5-flash-preview-tts	Fast, good quality, general use
gemini-2.5-pro-preview-tts	Highest quality, complex performances

Voices

30 prebuilt voices:

Voice	Gender	Character	Pitch
Achernar	Female	Soft	Higher
Achird	Male	Friendly	Lower middle
Algenib	Male	Gravelly	Lower
Algieba	Male	Smooth	Lower
Alnilam	Male	Firm	Lower middle
Aoede	Female	Breezy	Middle
Autonoe	Female	Bright	Middle
Callirrhoe	Female	Easy-going	Middle
Charon	Male	Informative	Lower
Despina	Female	Smooth	Middle
Enceladus	Male	Breathy	Lower
Erinome	Female	Clear	Middle
Fenrir	Male	Excitable	Lower middle
Gacrux	Female	Mature	Middle
Iapetus	Male	Clear	Lower middle
Kore	Female	Firm	Middle
Laomedeia	Female	Upbeat	Higher
Leda	Female	Youthful	Higher
Orus	Male	Firm	Lower middle
Puck	Male	Upbeat	Middle
Pulcherrima	Male	Forward	Middle
Rasalgethi	Male	Informative	Middle
Sadachbia	Male	Lively	Lower
Sadaltager	Male	Knowledgeable	Middle
Schedar	Male	Even	Lower middle
Sulafat	Female	Warm	Middle
Umbriel	Male	Easy-going	Lower middle
Vindemiatrix	Female	Gentle	Middle
Zephyr	Female	Bright	Higher
Zubenelgenubi	Male	Casual	Lower middle

Director's Notes (--director-notes)

Performance guidance for the selected voice. Define only what matters — overspecifying limits the model's creativity and can worsen results.

The three most common directions are Style, Pacing, and Accent, but you can include any custom instructions relevant to the performance.

• Style — Emotional quality and delivery character. Be descriptive: "Infectious enthusiasm — the listener should feel part of something exciting" works better than just "energetic". You can layer characteristics and use voiceover industry terms like "vocal smile".
• Pacing — Overall speed and rhythm variation. Can range from "Speak as fast as possible" to "Incredibly slow and liquid, words bleed into each other, zero urgency".
• Accent — Be specific. "British English as heard in Croydon, England" works much better than "British accent".

--director-notes "Style: Enthusiastic and sassy GenZ beauty YouTuber. Pacing: Extremely fast, rapid delivery like short-form video influencers. Accent: Southern California valley girl from Laguna Beach."

Audio Tags

Inline [brackets] in segment text for per-word control. Override director-notes locally.

[whispers] [shouting] [excited] [serious] [short pause] [laughs] [very fast] [very slow] [sarcastic] [curious]

Creative tags work too: [like dracula], [whispering conspiratorially]

Example: "[excited] This changes everything! [short pause] Let me show you how."

References

• Prompting Guide — Advanced prompt engineering for style, emotion, and accent