onnxvoice

onnxvoice is the published Python infrastructure package for shared ONNX voice-model catalogs, asset installation, integrity verification, ONNX Runtime sessions, and model tensor-contract execution.

Install the package and an optional ONNX Runtime provider with:

pip install onnxvoice
pip install "onnxvoice[cpu]"
pip install "onnxvoice[gpu]"
pip install "onnxvoice[directml]"
pip install "onnxvoice[openvino]"

Model catalogs and model artifacts remain external data. onnxvoice does not bundle model files or speech-engine policy.

Why

Without a shared layer, each TTS package tends to implement its own catalog client, download logic, cache directory, checksums, ONNX Runtime provider handling and model-specific inference glue. onnxvoice centralizes that middle layer.

The cache is content-addressed:

~/.cache/onnxvoice/
├── blobs/sha256/ab/abcdef...
├── catalogs/
│   ├── kokoro.json
│   └── piper.json
└── installs/
    ├── kokoro/v1.0/manifest.json
    └── piper/en_US-lessac-medium/manifest.json

Installations hard-link to immutable blobs when the platform and filesystem support hard links. Otherwise onnxvoice falls back to copying the verified blob into the installation directory. The blob cache remains content-addressed; copy-mode installations may use additional disk space. The same bytes therefore do not need to be stored twice by different model installations.

Stable low-level contract

Milestone A defines the dependency boundary used by downstream frontends:

• Installation manifests use schema 2 and preserve artifact component, format, quality, and metadata fields. Schema 1 manifests remain readable.
• System, item, and artifact paths are validated before filesystem access.
• Installations, catalog writes, blob publication, and garbage collection use process locks. Interrupted staging is removed.
• Asset operations accept progress callbacks receiving AssetProgress events.
• The canonical inference result is float32, one-dimensional NumPy audio with a positive sample rate. Kokoro timing and named auxiliary outputs are available on the result.
• open() resolves and verifies an existing installation only. open_local() uses explicit local files without copying them into the shared cache. Call install() explicitly for catalog access and downloads.
• Provider names support aliases such as cpu, cuda, gpu, directml, and openvino. Use auto for deterministic priority selection, or set ONNXVOICE_PROVIDER / ONNXVOICE_PROVIDERS for an environment policy.
• Provider names support aliases cpu, cuda, gpu, directml, dml, openvino, coreml, nnapi, and xnnpack, plus canonical ONNX Runtime names. Use auto for the documented deterministic priority policy, or set ONNXVOICE_PROVIDER / ONNXVOICE_PROVIDERS for an explicit environment policy. The coreml, nnapi, xnnpack, and mobile extras are markers because compatible platform ONNX Runtime builds supply those providers.

The shared cache is never required for importing the package. Offline mode reads existing catalog and blob data only and does not make network requests.

Stable voice selectors

Short voice selectors are persisted identity aliases, not positions in the current catalog. The canonical form is <language-key>-<engine-code>-<slot>:

de-ko-1       -> kokoro:de-anna, logical voice df_anna
de-pi-1       -> piper:de_DE-eva_k-x_low
en_us-ko-1    -> kokoro:v1.0, voice af_alloy
en_us-ko-4    -> kokoro:v1.0, voice af_heart
en_us-ko-26   -> kokoro:v1.1-zh, voice af_maple

For Kokoro catalog filtering, the input locale may use a hyphen, while the persisted selector uses the canonical underscore language key:

language filter/input locale: en-us or en-US
canonical selector language key: en_us

ko is the permanent Kokoro code and pi is the permanent Piper code. Slots are append-only and remain reserved when a voice is removed, so catalog insertion, sorting, filtering, installation state, and network availability cannot silently rename an existing selector. Use the selector API to resolve the complete identity:

from onnxvoice import resolve_voice_selector

identity = resolve_voice_selector("de-ko-1")
assert identity.backing_ref == "kokoro:de-anna"
assert identity.voice_id == "df_anna"

Asset operations still use canonical system:id references such as kokoro:de-anna and piper:de_DE-eva_k-x_low. Resolving a Kokoro selector does not choose a style tensor; producer packages remain responsible for style/policy selection. Catalog voices without registry assignments are reported as unassigned rather than receiving a runtime-generated number.

Install

The base package does not install ONNX Runtime. Choose the extra for the deployment provider:

pip install onnxvoice
pip install "onnxvoice[cpu]"
pip install "onnxvoice[gpu]"
pip install "onnxvoice[directml]"
pip install "onnxvoice[openvino]"

For development, install onnxvoice[dev,cpu].

The MVP directly understands the existing catalogs from:

• buchwandler/piper-onnx-voices (catalog/voices.json)
• buchwandler/kokoro-onnx-models (catalog/models.json)

Override them without changing code:

export ONNXVOICE_PIPER_CATALOG=/path/to/voices.json
export ONNXVOICE_KOKORO_CATALOG=/path/to/models.json

A local path or HTTP(S) URL is accepted.

CLI

Inventory and discovery

# Everything installed locally
onnxvoice installed

# Installed US English voices
onnxvoice installed --kind voice --lang en-US

# Installed male US English voices
onnxvoice installed --kind voice --lang en-US --gender male

# Installed + available male US English voices (merged inventory)
onnxvoice list --kind voice --lang en-US --gender male

# Only available (not installed) entries
onnxvoice list --status available

# JSON output for scripting
onnxvoice installed --format json

Updates

# Check what's outdated (refreshes catalogs by default)
onnxvoice updates

# Check against cached catalogs only
onnxvoice updates --cached

# Update one asset (preserves quality/distribution selection)
onnxvoice update piper:en_US-lessac-medium

# Update all outdated assets
onnxvoice update --all

Storage

# Show cache usage with byte totals
onnxvoice cache info

# Show cache usage as JSON
onnxvoice cache info --format json

# Show what GC would remove
onnxvoice cache gc --dry-run

# Remove orphaned blobs
onnxvoice cache gc

Removal

# Show what would be removed (dry run)
onnxvoice remove piper:en_US-lessac-medium --dry-run

# Remove one asset
onnxvoice remove piper:en_US-lessac-medium

# Remove and clean up orphaned blobs
onnxvoice remove piper:en_US-lessac-medium --gc

# Remove multiple assets
onnxvoice remove piper:en_US-lessac-medium kokoro:v1.0

# Remove all variants of a ref
onnxvoice remove kokoro:v1.0 --all-variants --yes

Info

# Detailed info about an installed asset
onnxvoice info piper:en_US-lessac-medium

# Info with update check
onnxvoice info piper:en_US-lessac-medium --check-updates

Install and verify

onnxvoice install piper:en_US-lessac-medium
onnxvoice install kokoro:v1.0 --quality fp16
onnxvoice path piper:en_US-lessac-medium
onnxvoice verify piper:en_US-lessac-medium
onnxvoice show piper:en_US-lessac-medium

Catalog management

onnxvoice catalog piper build --output catalog/voices.json --source-output catalog/source.json
onnxvoice catalog piper verify --catalog catalog/voices.json --source catalog/source.json

Filter flags

Common flags for list, installed, and updates:

| Flag | Description | | --------------------- | --------------------------------------- | ------- | ---------------------------- | ---------------- | | --system piper | kokoro | pocket | Filter by system | | --kind voice | model | bundle | Filter by kind | | --lang / --language | Filter by language (e.g. en, en-US) | | --gender male | female | neutral | unknown | Filter by gender | | --quality | Filter by quality | | --distribution | Filter by distribution | | --status installed | available | local | Filter by status (list only) | | --format table | plain | json | tsv | Output format |

Note on gender: Gender metadata depends on authoritative catalog sources. If the catalog does not supply a gender field, entries default to unknown. The CLI never infers gender from voice names or IDs.

Note on installed vs cached blobs: After onnxvoice remove REF, the installation is gone but content-addressed blobs may remain until onnxvoice cache gc is run. Use cache info to see reclaimable space.

Kokoro has multiple ONNX model qualities in one distribution. onnxvoice install kokoro:v1.0 selects fp32 by default rather than downloading all model variants. Non-model runtime artifacts from the selected distribution are installed with it.

Python API

Discover and install

from onnxvoice import OnnxVoice

ov = OnnxVoice()

for voice in ov.list("piper", language="en_US"):
    print(voice.ref)

piper = ov.install("piper:en_US-lessac-medium")
kokoro = ov.install("kokoro:v1.0", quality="fp16")

print(ov.where("piper:en_US-lessac-medium"))
print([item.ref for item in ov.installed()])

Piper inference

onnxvoice expects already-tokenized Piper IDs and a model-ready numeric speaker ID when the graph has a sid input. It does not phonemize text or resolve speaker names.

from onnxvoice import open

runtime = open("piper:en_US-lessac-medium")
result = runtime.infer(
    [1, 20, 14, 5, 2],
    speaker_id=0,
    length_scale=1.0,
    noise_scale=0.667,
    noise_w=0.8,
)

print(result.audio.dtype)
print(result.sample_rate)
runtime.close()

Kokoro inference

Kokoro receives an explicit model-ready style tensor. Logical voice selection and style archives belong to the higher-level engine.

runtime = open("kokoro:v1.0", quality="fp16")
result = runtime.infer(
    [50, 31, 12, 99],
    style=style_tensor,
    speed=1.0,
)
print(result.audio.shape, result.sample_rate)
runtime.close()

Pocket inference

Pocket bundles use the canonical pocket-onnx-bundles catalog and select a complete quality profile, including the mixed-precision int8 profile:

import numpy as np
from onnxvoice import OnnxVoice

ov = OnnxVoice()
installation = ov.install("pocket:english_2026-04", quality="int8")
with ov.open(installation, provider="cpu") as runtime:
    voice = runtime.prepare_voice(reference_audio, sample_rate=24000)
    result = runtime.infer(
        token_ids,
        voice_state=voice,
        temperature=0.7,
        lsd_steps=1,
        max_frames=200,
    )

prepare_voice() runs the Mimi encoder once and returns reusable voice embeddings. Each infer() call creates fresh Flow-LM and Mimi recurrent state. max_frames is a generation-frame limit, not a token or sample limit; frames_after_eos can request bounded post-EOS frames. Runtime opening validates the named graph inputs, outputs, and state manifests before inference.

For explicit local files, use the existing unmanaged boundary without catalog or HTTP access:

with OnnxVoice.open_local(
    system="pocket",
    files={
        "bundle_metadata": "bundle.json",
        "bos_conditioning": "bos_before_voice.npy",
        "mimi_encoder": "mimi_encoder.onnx",
        "text_conditioner": "text_conditioner.onnx",
        "flow_lm_main": "flow_lm_main.onnx",
        "flow_lm_flow": "flow_lm_flow.onnx",
        "mimi_decoder": "mimi_decoder.onnx",
    },
    metadata=bundle_metadata,
    sample_rate=24000,
    provider="cpu",
) as runtime:
    result = runtime.infer(token_ids, voice_state=runtime.prepare_voice(audio, sample_rate=24000))

The optional real-bundle smoke test is enabled by setting ONNXVOICE_POCKET_BUNDLE_DIR to a checked-out pinned bundle directory; otherwise it is skipped while fake-session contract tests remain mandatory. The same call works for the catalog's split-onnx-v1 layout. The frontend still supplies token IDs and a complete style row; OnnxVoice does not select voices or phonemize text.

Local split Kokoro

runtime = open_local(
    system="kokoro",
    artifacts={
        "prosody": "prosody.onnx",
        "curves": "curves.onnx",
        "decoder": "decoder.onnx",
        "voices": "voices.npz",
        "config": "manifest.json",
        "source_params": "source-params.npz",
    },
    runtime={"layout": "split-onnx-v1"},
    sample_rate=24000,
    provider="cpu",
)
result = runtime.infer(token_ids, style=style, speed=1.0, seed=1234)

Runtime diagnostics are available through runtime.diagnostics() for both single and multi-session layouts.

External/local models

External files can be imported into the same store:

ov.import_model(
    system="piper",
    item_id="my-voice",
    model="voice.onnx",
    config="voice.onnx.json",
)

runtime = ov.open("piper:my-voice")

For Kokoro:

ov.import_model(
    system="kokoro",
    item_id="my-kokoro",
    model="kokoro.onnx",
    voices="voices.npz",
    sample_rate=24000,
)

Local files can be opened without cache registration:

from onnxvoice import open_local

runtime = open_local(
    system="piper",
    model="voice.onnx",
    config="voice.onnx.json",
    provider="cpu",
)

The unmanaged runtime keeps the original file paths. Use import_model() when a durable managed installation and manifest are required.

System adapters

A TTS system adapter owns only the model-specific ONNX contract. It does not own text normalization, G2P, sentence splitting or document planning.

from onnxvoice.systems import SystemAdapter, register_adapter


class MyTTSAdapter(SystemAdapter):
    system = "mytts"
    ...


register_adapter("mytts", MyTTSAdapter)

The built-in MVP adapters are piper and kokoro.

Validation levels

The MVP includes three inexpensive building blocks:

• installed asset verification: file presence, size and SHA-256
• ONNX load/contract smoke check via ONNX Runtime
• returned audio sanity: numeric, finite and non-silent

Release-grade waveform parity, spectral gates and reference comparisons belong in a later validation layer. They should not run on every inference.

Architecture

PyKokoro / PiperSynth / another frontend
             │
             │ tokens + voice/model choice
             ▼
        onnxvoice
        ├── CatalogClient
        ├── AssetStore
        ├── SystemAdapter
        │   ├── PiperAdapter
        │   ├── KokoroAdapter
        │   └── SplitKokoroRuntime (prosody / curves / decoder)
        ├── OnnxSession
        └── validation
             │
             ▼
        NumPy audio

UtterRender should normally consume PyKokoro/PiperSynth and let those packages use onnxvoice underneath, rather than becoming another downloader/cache owner.

Versioning

The project uses setuptools_scm. There is no hard-coded project version and no src/ layout. Tagged Git commits produce package versions dynamically. A source tree without SCM metadata falls back to 0.1.0.

Current limitations

The current release supports the built-in Piper and Kokoro catalog formats, single-file Kokoro, and the first-class split-onnx-v1 multi-component Kokoro layout. Catalog distributions are selectable by identifier and cached with distinct identities. Resumable downloads, general third-party catalog schemas, and release-grade waveform parity gates remain separate work.

License

The onnxvoice source code is Apache-2.0. Downloaded models, voice packs and model cards retain their own licenses and terms; installing them through onnxvoice does not relicense those artifacts.