laion/SNAC-24khz-decoder-onnx

SNAC 24 kHz — Decoder as ONNX (browser-ready)

This repo provides ONNX decoders for the SNAC 24 kHz codec so you can decode SNAC tokens on-device, including in the browser with onnxruntime-web.

Why? If your TTS front-end is a decoder-only Transformer (e.g. Orpheus-style) that can stream out SNAC tokens fast and cheaply, you can keep synthesis private and responsive by decoding the audio in the user’s browser/CPU (or WebGPU when available).

In a Colab CPU test, we saw ~2.1× real-time decoding for a longer file using the ONNX model (inference time only, excluding model load). Your mileage will vary with hardware and browser.

Files

• snac24_int2wav_static.onnx — int → wav decoder
  Inputs (int64):

  • codes0: [1, 12]
  • codes1: [1, 24]
  • codes2: [1, 48]
    Output:
  • audio: float32 [1, 1, 24576] (24 kHz)

  Shapes correspond to a 48-frame window. Each frame is 512 samples, so one window = 24576 samples ≈ 1.024 s at 24 kHz.
  Token alignment: L0*4 = L1*2 = L2*1 = shared_frames.

• snac24_latent2wav_static.onnx — latent → wav decoder
  Input: z float32 [1, 768, 48] → Output: audio [1, 1, 24576]
  Use this if you reconstruct the latent yourself (RVQ embeddings + 1×1 conv projections).

• snac24_codes.json — sample codes (for testing)

• snac24_quantizers.json — RVQ metadata/weights (stride + embeddings + 1×1 projections) to reconstruct z if needed.

Browser (WASM/WebGPU) quickstart

Serve these files from a local server with cross-origin isolation for multithreaded WASM (e.g., COOP/COEP headers). If not isolated, WASM will typically run single-threaded.

Streaming note

SNAC is streamable in principle. For practical low-latency TTS, emit ~200 ms of tokens, decode in ~100 ms,
start playback, and continue decoding subsequent chunks; cross-fade a few ms to hide seams.

Threads / GPU

Multithreaded WASM requires cross-origin isolation (COOP/COEP). Without it, browsers typically run single-threaded.

WebGPU can accelerate on desktop and mobile when kernels are supported; this model usually falls back to WASM if not.