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Gemini Tts

Documents
gemini-tts

Gemini Tts is an Agent Skill for documents published in the sonichi/sutando repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.

Render text to mp3 via Google Gemini Flash TTS. Free-tier eligible (1500 req/day). Use for video narration, demo voiceovers, audio notes. Parallels openai-tts; default for make-viral-video.

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How to use this skill

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  2. Copy and paste the prompt below.
  3. Review files and risks before approving any action.
Prompt to paste
Inspect the Agent Skill at https://github.com/sonichi/sutando/blob/HEAD/skills/gemini-tts/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/gemini-tts, but wait for my approval before writing files or running scripts.

Copying this prompt does not install or run the skill. Review third-party files before use.

Gemini TTS

Synthesize speech via Google's gemini-2.5-flash-preview-tts (or -pro-tts / -lite-preview-tts per env override). Reads GEMINI_API_KEY from .env.

This is offline synthesis — distinct from voice-agent's bidirectional Gemini Live audio. Same model family, different surface (POST text → get audio bytes back, no streaming).

Usage: /gemini-tts [text]

ARGUMENTS: $ARGUMENTS

Voices

Aoede (default — alto, neutral), Charon (baritone, news-anchor), Kore (mid, expressive), Puck (high, conversational). Per Lucy's 2026-05-09 testing: Aoede is the closest match to OpenAI's sage.

Audio tags for expression

Inline bracket tags like [whispers], [excitedly], [slowly] are interpreted as stylistic direction, not spoken literally. Empirically verified against gemini-2.5-flash-preview-tts (per PR #646 comment): [whispers] hello → 1.05s audio; hello alone → 1.01s. If the tag were spoken literally as 8 words, the clip would be ~5× longer.

bash "$SKILL_DIR/scripts/synthesize.sh" -- "[whispers] Pull request 691 has landed."

Model selection

Default: gemini-2.5-flash-preview-tts (free tier, 1500 req/day, $0 within quota).

Override via GEMINI_TTS_MODEL env var:

  • gemini-2.5-pro-tts — paid, higher fidelity
  • gemini-2.5-flash-lite-preview-tts — preview, faster
  • gemini-3.1-flash-tts-preview — preview

Examples

bash "$SKILL_DIR/scripts/synthesize.sh" -- "Hello, this is Sutando."
bash "$SKILL_DIR/scripts/synthesize.sh" --voice Charon --out /tmp/intro.mp3 -- "Hi."
GEMINI_TTS_MODEL=gemini-2.5-pro-tts bash "$SKILL_DIR/scripts/synthesize.sh" -- "High-fidelity narration."

Default output path: results/gemini-tts-{epoch}.mp3.

Cost

Free tier: $0 within 1500 req/day quota. For our cadence (a few demos a day), stays free indefinitely. Paid (Flash): $0.50 / 1M input tokens + $10.00 / 1M output tokens.

Compared to OpenAI TTS (gpt-4o-mini-tts) at ~$0.02 per 60s: Gemini Flash is free-equivalent for typical demo workloads.

When to fall back to openai-tts

The make-viral-video skill auto-falls-back to OpenAI TTS when:

  • Gemini API returns 4xx/5xx
  • Gemini quota hit (429)
  • GEMINI_API_KEY missing
  • TTS_PROVIDER=OPENAI env override set

If Invoked As A Slash Command

If ARGUMENTS is empty, ask the user for the text. Otherwise:

bash "$SKILL_DIR/scripts/synthesize.sh" -- "$ARGUMENTS"