TTS Plugins¶

In a nutshell

TTS stands for Text-to-Speech: this is the part that gives your assistant its voice, turning written replies into spoken audio you can hear. It is the opposite of dictation. Instead of listening to you, it talks back. Different TTS plugins offer different voices and qualities, and some run on your own device while others use a cloud service. See the Glossary for related terms.

Writing a plugin instead of choosing one? See Writing a TTS Plugin.

Formal specification

TTS sits inside the audio output service, specified by OVOS-AUDIO-1: Audio Output Service: an ovos.utterance.speak response runs through the dialog-transformer chain → TTS → tts-transformer chain → playback queue. See the spec index.

TTS plugins are responsible for converting text into audio for playback.

flowchart TD
    A[sentence] --> B["get_tts(sentence,<br/>wav_file)"]
    B --> C["audio file (audio_ext)"]
    C --> D["cache, keyed by<br/>sentence hash"]
    D --> E["play_wav/ogg/mp3_cmdline"]
    B --> F[phonemes]
    F --> G["viseme()"]
    G --> H[mouth animation]

Diagram: The flow starts at the input sentence and ends at either playback or mouth animation, and get_tts() branches the output into an audio file for the playback commands and a phoneme list for the viseme mouth animation.

Audio format contract

A TTS plugin is the producer end of the audio path, so it picks the format rather than receiving one. get_tts() writes a complete, self-describing audio file to the path it is handed and returns that path. The container format must match the plugin's audio_ext (default "wav", set via the TTS.__init__ argument), because audio_ext is what names the cache file and what playback dispatches on.

Sample rate, bit depth and channel count are the plugin's own choice and travel inside the file's header. Nothing between get_tts() and the speakers resamples, remixes or re-encodes the audio, so whatever the engine emits is what is played. The one constraint is that the deployment must have a player for the extension: playback shells out to the command configured as play_wav_cmdline, play_ogg_cmdline or play_mp3_cmdline (falling back to a detected system player), so wav, ogg and mp3 are the extensions a stock deployment can play. Plain 16-bit mono WAV is the safe default.

get_tts() returns the tuple (audio_path, phonemes). phonemes is optional. Return None when the engine exposes none. When present it is a space-separated string of phoneme:duration pairs, which the base class's viseme() converts into a list of (viseme_code, duration_seconds) tuples for mouth animation.

A pair with no :duration is given 0.2 s. Both the audio and the phonemes are cached together, keyed by sentence hash.

Recommended: phoonnx

For fully offline, on-device synthesis, ovos-tts-plugin-phoonnx is the recommended starting point: it's OVOS's own ONNX-based multilingual neural TTS engine, installed with a single pip install phoonnx, and it fetches its model automatically the first time a voice is used. No separate download step. Cloud plugins like ovos-tts-plugin-polly, ovos-tts-plugin-azure, ovos-tts-plugin-edge-tts or ovos-tts-plugin-google-tx are a fair choice when you need a specific commercial voice or don't want to spend local compute on synthesis.

Footprint: phoonnx voices are small, single-purpose ONNX models. The class of model ONNX Runtime is built to run efficiently on-device, unlike the heavier general-purpose engines further down this page (Coqui, Whisper-class transformers, etc.). Exact size varies per voice, since each one is a separate model fetched on first use.

Licensing: the phoonnx code is Apache-2.0, but individual voices carry their own model-card terms — for a commercial or redistributed product, check the model card of every voice you ship, not just the code license. See Licensing.

Change your voice¶

Browse voices_demo for audio samples of the available TTS voices, or check a plugin's own catalog entry below for what it offers.
Open ~/.config/mycroft/mycroft.conf (create it if it doesn't exist) and set the tts section's module to the plugin you want, plus any plugin-specific settings (voice name, speaker id, etc.):
```
{
 "tts": {
   "module": "ovos-tts-plugin-phoonnx"
 }
}
```
Leaving out a "voice" key like this is a valid, minimal config. The plugin picks the first bundled model that supports the configured language. See the ovos-tts-plugin-phoonnx entry for how to pin a specific voice.

Installing a plugin's package (like pip install phoonnx) only makes it available to OVOS if it lands in the same Python environment OVOS itself runs in. Activate that venv or container first, the same way Your First Skill does before installing a skill.
Save the file. It's JSONC (comments allowed). Restart OVOS for the change to take effect.

Tip

Don't want to hand-pick a plugin and voice yourself? ovos-config autoconfigure -l <lang> ... picks a recommended offline/online voice for your language automatically. See Language Support.

TTS Plugins Reference¶

Code license is the SPDX license of the plugin's own repository. Where the plugin wraps a separately-licensed model or a paid cloud service, that is called out under "model".

Plugin	Description	License	Maturity
ovos-tts-server	Turn any OVOS TTS plugin into a micro service!	Apache-2.0	Stable
ovos-tts-plugin-polly	Amazon Polly cloud text-to-speech.	Apache-2.0 (cloud service, separate Amazon terms)	Mature
ovos-tts-plugin-google-tx	OVOS TTS plugin for gTTS	Apache-2.0 (cloud service, unofficial Google endpoint, separate Google terms)	Mature
ovos-tts-plugin-edge-tts	TTS plugin for OVOS based on Edge-TTS	Apache-2.0	Stable
ovos-tts-plugin-matxa-multispeaker-cat	Matxa-TTS, the multispeaker, multidialectal neural TTS model. It works together with the vocoder model alVoCat to generate speech in four Catalan dialects. Warning: archived, deprecated.	Apache-2.0 (model: see model card)	Deprecated
ovos-tts-plugin-marytts	TTS Plugin for MaryTTS	Apache-2.0	Stable
ovos-tts-plugin-piper	Offline neural TTS with the Piper engine. Default TTS on the raspOVOS hybrid/offline images. Warning: archived, deprecated — phoonnx is the maintained successor.	Apache-2.0	Deprecated
ovos-tts-plugin-espeakNG	eSpeak NG offline text-to-speech (robotic, supports many languages).	GPL-3.0	Mature
ovos-tts-plugin-beepspeak	Novelty R2-D2-style beep text-to-speech.	see repo (no license file)	Stable
ovos-tts-plugin-cotovia	OVOS TTS plugin for Cotovia TTS	Apache-2.0	Mature
ovos-tts-plugin-mimic	OVOS TTS plugin for Mimic	Apache-2.0	Mature
ovos-tts-plugin-SAM	S.A.M., Software Automatic Mouth, the classic retro speech synthesizer.	see repo (no license file)	Mature
ovos-tts-plugin-azure	This TTS service for OpenVoiceOS requires a subscription to Microsoft Azure and the creation of a Speech resource (https://docs.microsoft.com/en-us/azure/cognitive-services/speech-service/overview#create-the-azure-resource)	Apache-2.0 (cloud service, separate Microsoft terms)	Stable
ovos-tts-plugin-ahotts	OVOS TTS plugin for AhoTTS	Apache-2.0	Stable
ovos-tts-plugin-server	Companion plugin for an OVOS TTS Server. Install name is `ovos-tts-plugin-server`; the repo is `ovos-tts-server-plugin` (words swapped). Uses public community servers unless you set `host`	Apache-2.0	Mature
ovos-tts-plugin-coqui	OVOS TTS plugin for Coqui TTS	Apache-2.0	Stable
ovos-tts-plugin-pico	SVOX Pico lightweight offline text-to-speech.	Apache-2.0	Mature
ovos-tts-plugin-lux	LuxTTS: zipvoice-based voice-cloning TTS (48 kHz, en-US). (not yet packaged, no dedicated section, see repo)	Apache-2.0	Beta
ovos-tts-plugin-phoonnx	Built into phoonnx, OVOS's own ONNX-based multilingual neural TTS engine. It is the default choice for fully offline synthesis, with automatic model fetching.	Apache-2.0 (code); models: see model card	Stable
ovos-tts-plugin-omnivoice	Wraps OmniVoice, a massively multilingual (600+ languages) zero-shot TTS model with `auto`, voice-design (`instruct`), and voice-cloning (`ref_audio`) modes. (alpha on PyPI, no dedicated section, see repo)	Apache-2.0 (model: see model card)	Alpha

Maturity reflects repository health (age, activity, open issues/PRs, in-repo docs), not version. See the Maturity Scale.

License and Maturity are independent axes

The License column reports what the repository itself declares. "No license file" just means no SPDX license was found, not that the code is unmature. The Maturity column reports repository health (age, activity, issues/PRs, docs). A plugin can be Mature and still ship no license file. A plugin can be Stable with a permissive license but thin docs. Don't read one column as implying the other.

Choosing a TTS engine family¶

The engines behind the plugins fall into a few families with clear trade-offs. Links go to the architecture paper or the upstream project, where the authoritative training-data and licensing detail lives. Check the model card of every individual voice: code license and voice license routinely differ.

Piper / VITS voices (served through phoonnx; the standalone piper plugin is archived). Small per-voice ONNX models built on the VITS architecture: fast on CPU, low RAM, one model per voice, limited expressiveness. Upstream: rhasspy/piper.

phoonnx (recommended default). Not one architecture but a multi-format ONNX loader (TigreGotico/phoonnx): native voices plus Piper, Mimic 3, Coqui, MMS, and zero-shot cloning backbones, spanning 1000+ languages/voices with auto-fetch on first use. Naturalness and latency vary per underlying voice, and so does the voice license (the code is Apache-2.0; some bundled models are OpenRAIL-M).

Coqui (docs). A multi-architecture toolkit (VITS, XTTS, YourTTS, Bark, and more) with top naturalness and voice cloning, but transformer/diffusion-class weights that prefer a GPU for real-time use. MPL-2.0 code, per-model licenses vary.

Zero-shot cloning engines (lux/ZipVoice, omnivoice). Clone any voice from a few seconds of reference audio. OmniVoice (k2-fsa/OmniVoice, Apache-2.0) claims 600+ languages and ~40x real-time. LuxTTS is ZipVoice-based, English-only, GPU-oriented. Both are early-stage: promising, not proven for production.

Pre-neural engines (mimic, espeak-ng, pico, marytts). Mimic 1 (Festival/Flite concatenative) and espeak-ng (formant synthesis, 100+ languages, GPL-3.0) run on anything and start instantly, but sound unmistakably robotic. Mimic 1 remains uniquely useful as the only engine returning real phoneme timing for mouth animation, and espeak-ng is the accessibility/fallback pick. MaryTTS is a Java server with HMM voices.

Cloud voices (polly, azure, edge-tts, google-tx). No local compute, high quality, but speech text leaves the device, an account or API key is usually needed, and gTTS and edge-tts ride unofficial endpoints that can break without notice.

Learn more¶

Full technical detail per plugin (repository link, license notes, default configuration) lives on the TTS Plugins Reference page linked from the table above. Writing a plugin instead of choosing one? See Writing a TTS Plugin.