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hermes-agent/website/docs/user-guide/features/tts.md
Teknium 8d302e37a8 feat(tts): add Piper as a native local TTS provider (closes #8508) (#17885) 
Piper (OHF-Voice/piper1-gpl) is a fast, local neural TTS engine from the
Home Assistant project that supports 44 languages with zero API keys.
Adds it as a native built-in provider alongside edge/neutts/kittentts,
installable via 'hermes tools' with one keystroke.

What ships:

- New 'piper' built-in provider in tools/tts_tool.py
  - Lazy import via _import_piper()
  - Module-level voice cache keyed on (model_path, use_cuda) so switching
    voices doesn't invalidate older cached voices
  - _resolve_piper_voice_path() accepts either an absolute .onnx path or a
    voice name (auto-downloaded on first use via 'python -m
    piper.download_voices --download-dir <cache>')
  - Voice cache at ~/.hermes/cache/piper-voices/ (profile-aware via
    get_hermes_dir)
  - Optional SynthesisConfig knobs: length_scale, noise_scale,
    noise_w_scale, volume, normalize_audio, use_cuda — passed through
    only when configured, so older piper-tts versions aren't broken
  - WAV output then ffmpeg conversion path (same as neutts/kittentts) so
    Telegram voice bubbles work when ffmpeg is present
  - Piper added to BUILTIN_TTS_PROVIDERS so a user's
    tts.providers.piper.command cannot shadow the native provider
    (regression test included)

- 'hermes tools' wizard entry
  - Piper appears under Voice and TTS as local free, with
    'pip install piper-tts' auto-install via post_setup handler
  - Prints voice-catalog URL and default-voice info after install

- config.yaml defaults
  - tts.piper.voice defaults to en_US-lessac-medium
  - Commented advanced knobs for discoverability

- Docs
  - New 'Piper (local, 44 languages)' section in features/tts.md
    explaining install path, voice switching, pre-downloaded voices,
    and advanced knobs
  - Piper listed in the ten-provider table and ffmpeg table
  - Custom-command-providers section updated to drop the Piper example
    (now native) and add a piper-custom example for users with their own
    trained .onnx models
  - overview.md bumps provider count to ten

- Tests (tests/tools/test_tts_piper.py, 16 tests)
  - Registration (BUILTIN_TTS_PROVIDERS, PROVIDER_MAX_TEXT_LENGTH)
  - _resolve_piper_voice_path across every branch: direct .onnx path,
    cached voice name, fresh download with correct CLI args, download
    failure, successful-exit-but-missing-files, empty voice to default
  - _generate_piper_tts: loads voice once, reuses cache, voice-name
    download wiring, advanced knobs flow through SynthesisConfig
  - text_to_speech_tool end-to-end dispatch and missing-package error
  - check_tts_requirements: piper availability toggles the return value
  - Regression guard: piper cannot be shadowed by a command provider
    with the same name
  - Pre-existing test_tts_mistral test broadened to mock the new
    piper/kittentts/command-provider checks (otherwise it false-passes
    when piper is installed in the test venv)

E2E verification (live):

Actual pip install piper-tts, config piper + en_US-lessac-low,
text_to_speech_tool call, voice auto-downloaded from HuggingFace,
WAV synthesized, ffmpeg-converted to Ogg/Opus. Second call hits the
cache (~60ms). Cache dir populated with .onnx and .onnx.json.

This caught a real bug during development: the first pass used '-d' as
the download-dir flag; the actual piper.download_voices CLI wants
'--download-dir'. Fixed before PR opened.
2026-04-30 02:53:20 -07:00

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---
sidebar_position: 9
title: "Voice & TTS"
description: "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.
:::tip Nous Subscribers
If you have a paid [Nous Portal](https://portal.nousresearch.com) subscription, OpenAI TTS is available through the **[Tool Gateway](tool-gateway.md)** without a separate OpenAI API key. Run `hermes model` or `hermes tools` to enable it.
:::
## Text-to-Speech
Convert text to speech with ten 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` |
| **MiniMax TTS** | Excellent | Paid | `MINIMAX_API_KEY` |
| **Mistral (Voxtral TTS)** | Excellent | Paid | `MISTRAL_API_KEY` |
| **Google Gemini TTS** | Excellent | Free tier | `GEMINI_API_KEY` |
| **xAI TTS** | Excellent | Paid | `XAI_API_KEY` |
| **NeuTTS** | Good | Free (local) | None needed |
| **KittenTTS** | Good | Free (local) | None needed |
| **Piper** | Good | Free (local) | None needed |
### Platform Delivery
| Platform | Delivery | Format |
|----------|----------|--------|
| Telegram | Voice bubble (plays inline) | Opus `.ogg` |
| Discord | Voice bubble (Opus/OGG), falls back to file attachment | Opus/MP3 |
| WhatsApp | Audio file attachment | MP3 |
| CLI | Saved to `~/.hermes/audio_cache/` | MP3 |
### Configuration
```yaml
# In ~/.hermes/config.yaml
tts:
provider: "edge" # "edge" | "elevenlabs" | "openai" | "minimax" | "mistral" | "gemini" | "xai" | "neutts" | "kittentts" | "piper"
speed: 1.0 # Global speed multiplier (provider-specific settings override this)
edge:
voice: "en-US-AriaNeural" # 322 voices, 74 languages
speed: 1.0 # Converted to rate percentage (+/-%)
elevenlabs:
voice_id: "pNInz6obpgDQGcFmaJgB" # Adam
model_id: "eleven_multilingual_v2"
openai:
model: "gpt-4o-mini-tts"
voice: "alloy" # alloy, echo, fable, onyx, nova, shimmer
base_url: "https://api.openai.com/v1" # Override for OpenAI-compatible TTS endpoints
speed: 1.0 # 0.25 - 4.0
minimax:
model: "speech-2.8-hd" # speech-2.8-hd (default), speech-2.8-turbo
voice_id: "English_Graceful_Lady" # See https://platform.minimax.io/faq/system-voice-id
speed: 1 # 0.5 - 2.0
vol: 1 # 0 - 10
pitch: 0 # -12 - 12
mistral:
model: "voxtral-mini-tts-2603"
voice_id: "c69964a6-ab8b-4f8a-9465-ec0925096ec8" # Paul - Neutral (default)
gemini:
model: "gemini-2.5-flash-preview-tts" # or gemini-2.5-pro-preview-tts
voice: "Kore" # 30 prebuilt voices: Zephyr, Puck, Kore, Enceladus, Gacrux, etc.
xai:
voice_id: "eve" # xAI TTS voice (see https://docs.x.ai/docs/api-reference#tts)
language: "en" # ISO 639-1 code
sample_rate: 24000 # 22050 / 24000 (default) / 44100 / 48000
bit_rate: 128000 # MP3 bitrate; only applies when codec=mp3
# base_url: "https://api.x.ai/v1" # Override via XAI_BASE_URL env var
neutts:
ref_audio: ''
ref_text: ''
model: neuphonic/neutts-air-q4-gguf
device: cpu
kittentts:
model: KittenML/kitten-tts-nano-0.8-int8 # 25MB int8; also: kitten-tts-micro-0.8 (41MB), kitten-tts-mini-0.8 (80MB)
voice: Jasper # Jasper, Bella, Luna, Bruno, Rosie, Hugo, Kiki, Leo
speed: 1.0 # 0.5 - 2.0
clean_text: true # Expand numbers, currencies, units
piper:
voice: en_US-lessac-medium # voice name (auto-downloaded) OR absolute path to .onnx
# voices_dir: '' # default: ~/.hermes/cache/piper-voices/
# use_cuda: false # requires onnxruntime-gpu
# length_scale: 1.0 # 2.0 = twice as slow
# noise_scale: 0.667
# noise_w_scale: 0.8
# volume: 1.0 # 0.5 = half as loud
# normalize_audio: true
```
**Speed control**: The global `tts.speed` value applies to all providers by default. Each provider can override it with its own `speed` setting (e.g., `tts.openai.speed: 1.5`). Provider-specific speed takes precedence over the global value. Default is `1.0` (normal speed).
### Telegram Voice Bubbles & ffmpeg
Telegram voice bubbles require Opus/OGG audio format:
- **OpenAI, ElevenLabs, and Mistral** produce Opus natively — no extra setup
- **Edge TTS** (default) outputs MP3 and needs **ffmpeg** to convert:
- **MiniMax TTS** outputs MP3 and needs **ffmpeg** to convert for Telegram voice bubbles
- **Google Gemini TTS** outputs raw PCM and uses **ffmpeg** to encode Opus directly for Telegram voice bubbles
- **xAI TTS** outputs MP3 and needs **ffmpeg** to convert for Telegram voice bubbles
- **NeuTTS** outputs WAV and also needs **ffmpeg** to convert for Telegram voice bubbles
- **KittenTTS** outputs WAV and also needs **ffmpeg** to convert for Telegram voice bubbles
- **Piper** outputs WAV and also needs **ffmpeg** to convert for Telegram voice bubbles
```bash
# Ubuntu/Debian
sudo apt install ffmpeg
# macOS
brew install ffmpeg
# Fedora
sudo dnf install ffmpeg
```
Without ffmpeg, Edge TTS, MiniMax TTS, NeuTTS, KittenTTS, and Piper audio are sent as regular audio files (playable, but shown as a rectangular player instead of a voice bubble).
:::tip
If you want voice bubbles without installing ffmpeg, switch to the OpenAI, ElevenLabs, or Mistral provider.
:::
### Piper (local, 44 languages)
Piper is a fast, local neural TTS engine from the Open Home Foundation (the Home Assistant maintainers). It runs entirely on CPU, supports **44 languages** with pre-trained voices, and needs no API key.
**Install via `hermes tools`** → Voice & TTS → Piper — Hermes runs `pip install piper-tts` for you. Or install manually: `pip install piper-tts`.
**Switch to Piper:**
```yaml
tts:
provider: piper
piper:
voice: en_US-lessac-medium
```
On the first TTS call for a voice that isn't cached locally, Hermes runs `python -m piper.download_voices <name>` and downloads the model (~20-90MB depending on quality tier) into `~/.hermes/cache/piper-voices/`. Subsequent calls reuse the cached model.
**Picking a voice.** The [full voice catalog](https://github.com/OHF-Voice/piper1-gpl/blob/main/docs/VOICES.md) covers English, Spanish, French, German, Italian, Dutch, Portuguese, Russian, Polish, Turkish, Chinese, Arabic, Hindi, and more — each with `x_low` / `low` / `medium` / `high` quality tiers. Sample voices at [rhasspy.github.io/piper-samples](https://rhasspy.github.io/piper-samples/).
**Using a pre-downloaded voice.** Set `tts.piper.voice` to an absolute path ending in `.onnx`:
```yaml
tts:
piper:
voice: /path/to/my-custom-voice.onnx
```
**Advanced knobs** (`tts.piper.length_scale` / `noise_scale` / `noise_w_scale` / `volume` / `normalize_audio`, `use_cuda`) correspond 1:1 to Piper's `SynthesisConfig`. They're ignored on older `piper-tts` versions.
### Custom command providers
If a TTS engine you want isn't natively supported (VoxCPM, MLX-Kokoro, XTTS CLI, a voice-cloning script, anything else that exposes a CLI), you can wire it in as a **command-type provider** without writing any Python. Hermes writes the input text to a temp UTF-8 file, runs your shell command, and reads the audio file the command produced.
Declare one or more providers under `tts.providers.<name>` and switch between them with `tts.provider: <name>` — the same way you switch between built-ins like `edge` and `openai`.
```yaml
tts:
provider: voxcpm # pick any name under tts.providers
providers:
voxcpm:
type: command
command: "voxcpm --ref ~/voice.wav --text-file {input_path} --out {output_path}"
output_format: mp3
timeout: 180
voice_compatible: true # try to deliver as a Telegram voice bubble
mlx-kokoro:
type: command
command: "python -m mlx_kokoro --in {input_path} --out {output_path} --voice {voice}"
voice: af_sky
output_format: wav
piper-custom: # native Piper also supports custom .onnx via tts.piper.voice
type: command
command: "piper -m /path/to/custom.onnx -f {output_path} < {input_path}"
output_format: wav
```
#### Placeholders
Your command template can reference these placeholders. Hermes substitutes them at render time and shell-quotes each value for the surrounding context (bare / single-quoted / double-quoted), so paths with spaces and other shell-sensitive characters are safe.
| Placeholder | Meaning |
|------------------|------------------------------------------------------|
| `{input_path}` | Path to the temp UTF-8 text file Hermes wrote |
| `{text_path}` | Alias for `{input_path}` |
| `{output_path}` | Path the command must write audio to |
| `{format}` | `mp3` / `wav` / `ogg` / `flac` |
| `{voice}` | `tts.providers.<name>.voice`, empty when unset |
| `{model}` | `tts.providers.<name>.model` |
| `{speed}` | Resolved speed multiplier (provider or global) |
Use `{{` and `}}` for literal braces.
#### Optional keys
| Key | Default | Meaning |
|--------------------|---------|------------------------------------------------------------------------------------------------------------|
| `timeout` | `120` | Seconds; the process tree is killed on expiry (Unix `killpg`, Windows `taskkill /T`). |
| `output_format` | `mp3` | One of `mp3` / `wav` / `ogg` / `flac`. Auto-inferred from the output extension if Hermes picks a path. |
| `voice_compatible` | `false` | When `true`, Hermes converts MP3/WAV output to Opus/OGG via ffmpeg so Telegram renders a voice bubble. |
| `max_text_length` | `5000` | Input is truncated to this length before rendering the command. |
| `voice` / `model` | empty | Passed to the command as placeholder values only. |
#### Behavior notes
- **Built-in names always win.** A `tts.providers.openai` entry never shadows the native OpenAI provider, so no user config can silently replace a built-in.
- **Default delivery is a document.** Command providers deliver as regular audio attachments on every platform. Opt in to voice-bubble delivery per-provider with `voice_compatible: true`.
- **Command failures surface to the agent.** Non-zero exit, empty output, or timeout all return an error with the command's stderr/stdout included so you can debug the provider from the conversation.
- **`type: command` is the default when `command:` is set.** Writing `type: command` explicitly is good practice but not required; an entry with a non-empty `command` string is treated as a command provider.
- **`{input_path}` / `{text_path}` are interchangeable.** Use whichever reads better in your command.
#### Security
Command-type providers run whatever shell command you configure, with your user's permissions. Hermes quotes placeholder values and enforces the configured timeout, but the command template itself is trusted local input — treat it the same way you would a shell script on your PATH.
## 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
```yaml
# In ~/.hermes/config.yaml
stt:
provider: "local" # "local" | "groq" | "openai" | "mistral" | "xai"
local:
model: "base" # tiny, base, small, medium, large-v3
openai:
model: "whisper-1" # whisper-1, gpt-4o-mini-transcribe, gpt-4o-transcribe
mistral:
model: "voxtral-mini-latest" # voxtral-mini-latest, voxtral-mini-2602
xai:
model: "grok-stt" # xAI Grok STT
```
### Provider Details
**Local (faster-whisper)** — Runs Whisper locally via [faster-whisper](https://github.com/SYSTRAN/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`.
**Mistral API (Voxtral Transcribe)** — Requires `MISTRAL_API_KEY`. Uses Mistral's [Voxtral Transcribe](https://docs.mistral.ai/capabilities/audio/speech_to_text/) models. Supports 13 languages, speaker diarization, and word-level timestamps. Install with `pip install hermes-agent[mistral]`.
**xAI Grok STT** — Requires `XAI_API_KEY`. Posts to `https://api.x.ai/v1/stt` as multipart/form-data. Good choice if you're already using xAI for chat or TTS and want one API key for everything. Auto-detection order puts it after Groq — explicitly set `stt.provider: xai` to force it.
**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
- **Mistral key/SDK not set** → Skipped in auto-detect; falls through to next available provider
- **Nothing available** → Voice messages pass through with an accurate note to the user
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