hermes-agent/website/docs/user-guide/features/tts.md

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9	Voice & TTS	Text-to-speech and voice message transcription across all platforms

Voice & TTS

Hermes Agent supports both text-to-speech output and voice message transcription across all messaging platforms.

Text-to-Speech

Convert text to speech with three providers:

Provider	Quality	Cost	API Key
Edge TTS (default)	Good	Free	None needed
ElevenLabs	Excellent	Paid	ELEVENLABS_API_KEY
OpenAI TTS	Good	Paid	VOICE_TOOLS_OPENAI_KEY

Platform Delivery

Platform	Delivery	Format
Telegram	Voice bubble (plays inline)	Opus .ogg
Discord	Audio file attachment	MP3
WhatsApp	Audio file attachment	MP3
CLI	Saved to ~/.hermes/audio_cache/	MP3

Configuration

# In ~/.hermes/config.yaml
tts:
  provider: "edge"              # "edge" | "elevenlabs" | "openai"
  edge:
    voice: "en-US-AriaNeural"   # 322 voices, 74 languages
  elevenlabs:
    voice_id: "pNInz6obpgDQGcFmaJgB"  # Adam
    model_id: "eleven_multilingual_v2"
  openai:
    model: "gpt-4o-mini-tts"
    voice: "alloy"              # alloy, echo, fable, onyx, nova, shimmer

Telegram Voice Bubbles & ffmpeg

Telegram voice bubbles require Opus/OGG audio format:

• OpenAI and ElevenLabs produce Opus natively — no extra setup
• Edge TTS (default) outputs MP3 and needs ffmpeg to convert:

# Ubuntu/Debian
sudo apt install ffmpeg

# macOS
brew install ffmpeg

# Fedora
sudo dnf install ffmpeg

Without ffmpeg, Edge TTS audio is sent as a regular audio file (playable, but shows as a rectangular player instead of a voice bubble).

:::tip If you want voice bubbles without installing ffmpeg, switch to the OpenAI or ElevenLabs provider. :::

Voice Message Transcription (STT)

Voice messages sent on Telegram, Discord, WhatsApp, Slack, or Signal are automatically transcribed and injected as text into the conversation. The agent sees the transcript as normal text.

Provider	Quality	Cost	API Key
Local Whisper (default)	Good	Free	None needed
Groq Whisper API	Good–Best	Free tier	GROQ_API_KEY
OpenAI Whisper API	Good–Best	Paid	VOICE_TOOLS_OPENAI_KEY or OPENAI_API_KEY

:::info Zero Config Local transcription works out of the box when faster-whisper is installed. If that's unavailable, Hermes can also use a local whisper CLI from common install locations (like /opt/homebrew/bin) or a custom command via HERMES_LOCAL_STT_COMMAND. :::

Configuration

# In ~/.hermes/config.yaml
stt:
  provider: "local"           # "local" | "groq" | "openai"
  local:
    model: "base"             # tiny, base, small, medium, large-v3
  openai:
    model: "whisper-1"        # whisper-1, gpt-4o-mini-transcribe, gpt-4o-transcribe

Provider Details

Local (faster-whisper) — Runs Whisper locally via faster-whisper. Uses CPU by default, GPU if available. Model sizes:

Model	Size	Speed	Quality
tiny	~75 MB	Fastest	Basic
base	~150 MB	Fast	Good (default)
small	~500 MB	Medium	Better
medium	~1.5 GB	Slower	Great
large-v3	~3 GB	Slowest	Best

Groq API — Requires GROQ_API_KEY. Good cloud fallback when you want a free hosted STT option.

OpenAI API — Accepts VOICE_TOOLS_OPENAI_KEY first and falls back to OPENAI_API_KEY. Supports whisper-1, gpt-4o-mini-transcribe, and gpt-4o-transcribe.

Custom local CLI fallback — Set HERMES_LOCAL_STT_COMMAND if you want Hermes to call a local transcription command directly. The command template supports {input_path}, {output_dir}, {language}, and {model} placeholders.

Fallback Behavior

If your configured provider isn't available, Hermes automatically falls back:

• Local faster-whisper unavailable → Tries a local whisper CLI or HERMES_LOCAL_STT_COMMAND before cloud providers
• Groq key not set → Falls back to local transcription, then OpenAI
• OpenAI key not set → Falls back to local transcription, then Groq
• Nothing available → Voice messages pass through with an accurate note to the user