---
license: apache-2.0
library_name: transformers
tags:
  - audio
  - audio-tokenizer
  - neural-codec
  - moss-tts-family
  - MOSS Audio Tokenizer
  - speech-tokenizer
  - trust-remote-code
---

# MossAudioTokenizer

This is the code for MOSS-Audio-Tokenizer presented in [MOSS-Audio-Tokenizer: Scaling Audio Tokenizers for Future Audio Foundation Models](https://arxiv.org/abs/2602.10934). 

**MOSSAudioTokenizer** is a unified discrete audio tokenizer based on the **Cat** (**C**ausal **A**udio **T**okenizer with **T**ransformer) architecture. Scaling to 1.6 billion parameters, it functions as a unified discrete interface, delivering both lossless-quality reconstruction and high-level semantic alignment.

**Key Features:**

*   **Extreme Compression & Variable Bitrate**: It compresses 48kHz stereo audio into a remarkably low frame rate of 12.5Hz. Utilizing a 32-layer Residual LFQ quantizer stack, it supports high-fidelity reconstruction across a wide range of bitrates.
*   **Pure Transformer Architecture**: The model features a "CNN-free" homogeneous architecture built entirely from Causal Transformer blocks. With 1.6B combined parameters (Encoder + Decoder), it ensures exceptional scalability and supports low-latency streaming inference.
*   **Large-Scale General Audio Training**: Trained on 3 million hours of diverse audio data, the model excels at encoding and reconstructing all audio domains, including speech, sound effects, and music.
*   **Unified Semantic-Acoustic Representation**: While achieving state-of-the-art reconstruction quality, Cat produces discrete tokens that are "semantic-rich," making them ideal for downstream tasks like speech understanding (ASR) and generation (TTS).
*   **Fully Trained From Scratch**: Cat does not rely on any pretrained encoders (such as HuBERT or Whisper) or distillation from teacher models. All representations are learned autonomously from raw data.
*   **End-to-End Joint Optimization**: All components—including the encoder, quantizer, decoder, discriminator, and a decoder-only LLM for semantic alignment—are optimized jointly in a single unified training pipeline.

**Summary:**
By combining a simple, scalable architecture with massive-scale data, the Cat architecture overcomes the bottlenecks of traditional audio tokenizers. It provides a robust, high-fidelity, and semantically grounded interface for the next generation of native audio foundation models.

This repository contains a lightweight remote-code implementation that mirrors the current 🤗 Transformers
`transformers.models.moss_audio_tokenizer` module. It is intended to be uploaded to a Hugging Face Hub model repository
and loaded with `trust_remote_code=True` when needed.


## Usage

### Quickstart

```python
import torch
from transformers import AutoModel
import torchaudio

repo_id = "OpenMOSS-Team/MOSS-Audio-Tokenizer"
model = AutoModel.from_pretrained(repo_id, trust_remote_code=True).eval()

wav, sr = torchaudio.load('demo/demo_gt.wav')
if sr != model.sampling_rate:
    wav = torchaudio.functional.resample(wav, sr, model.sampling_rate)
if wav.shape[0] == 1:
    wav = wav.repeat(model.config.number_channels, 1)
else:
    wav = wav[: model.config.number_channels]
wav = wav.unsqueeze(0)
enc = model.encode(wav, return_dict=True)
print(f"enc.audio_codes.shape: {enc.audio_codes.shape}")
dec = model.decode(enc.audio_codes, return_dict=True)
print(f"dec.audio.shape: {dec.audio.shape}")
wav = dec.audio.squeeze(0)
torchaudio.save("demo/demo_rec.wav", wav, sample_rate=model.sampling_rate)

# Decode using only the first 8 layers of the RVQ
dec_rvq8 = model.decode(enc.audio_codes[:8], return_dict=True)
wav_rvq8 = dec_rvq8.audio.squeeze(0)
torchaudio.save("demo/demo_rec_rvq8.wav", wav_rvq8, sample_rate=model.sampling_rate)
```

### Attention Backend And Compute Dtype

`config.attention_implementation` controls whether transformer layers prefer `sdpa` or `flash_attention_2`.
`config.compute_dtype` controls the non-quantizer autocast dtype and supports `fp32`, `bf16`, and `fp16`.

```python
model.set_attention_implementation("flash_attention_2")
model.set_compute_dtype("fp16")
```

The quantizer always runs in fp32.

### Streaming

`MossAudioTokenizerModel.encode`, `decode`, `batch_encode`, and `batch_decode` all support streaming through a
`chunk_duration` argument.

- `chunk_duration` is expressed in seconds.
- `chunk_duration * MossAudioTokenizerConfig.sampling_rate` must be divisible by `MossAudioTokenizerConfig.downsample_rate`.
- Streaming batch inference is supported.
- The public waveform interface expects stereo inputs shaped `(2, T)` or batched stereo inputs shaped `(B, 2, T)`.

```python
import torch
from transformers import AutoModel

repo_id = "OpenMOSS-Team/MOSS-Audio-Tokenizer"
model = AutoModel.from_pretrained(repo_id, trust_remote_code=True).eval()
audio = torch.randn(2, 48000 * 6)  # dummy stereo waveform

# 6.0s @ 48kHz = 288000 samples, divisible by downsample_rate=3840
enc = model.encode(audio.unsqueeze(0), return_dict=True, chunk_duration=0.08)
dec = model.decode(enc.audio_codes, return_dict=True, chunk_duration=0.08)

batch_enc = model.batch_encode([audio, audio[:, : 48000 * 3]], chunk_duration=0.08)
codes_list = [
    batch_enc.audio_codes[:, i, : batch_enc.audio_codes_lengths[i]]
    for i in range(batch_enc.audio_codes.shape[1])
]
batch_dec = model.batch_decode(codes_list, chunk_duration=0.08)
```

#### Continuous Batch Streaming Decode

For decoder-side continuous batching, prefer `batch_decode(..., streaming=True, ...)`.

- The first streaming call may pass `max_batch_size=...`. If it is omitted, the first batch size reserves the
  fixed-slot decoder budget for that public stream.
- Same-size calls continue the existing logical rows in-order.
- If a later call is larger, the new rows are admitted by tail append.
- `finalize_indices` means "decode these rows one last time, then evict them". The indices are interpreted against the
  pre-call logical order.
- After a finalize call returns, the next streaming call may use the smaller survivor batch.
- `reset_stream=True` discards the hidden public streaming state and starts a fresh stream.

Milestone 1 boundaries:

- decode-only continuous batching
- one active streaming decode state per model instance
- fixed-slot decoder reservation from `max_batch_size`
- no encode-side continuous batching
- no physical compaction of surviving decode slots
- no multi-session concurrency on one model instance

```python
import torch
from transformers import AutoModel

repo_id = "OpenMOSS-Team/MOSS-Audio-Tokenizer"
model = AutoModel.from_pretrained(repo_id, trust_remote_code=True).eval()
num_quantizers = model.config.quantizer_kwargs["num_quantizers"]

codes_a0 = torch.randint(0, 8, (num_quantizers, 2))
codes_b0 = torch.randint(0, 8, (num_quantizers, 3))
codes_a1 = torch.randint(0, 8, (num_quantizers, 2))
codes_b1 = torch.randint(0, 8, (num_quantizers, 2))
codes_c0 = torch.randint(0, 8, (num_quantizers, 1))
codes_a2 = torch.randint(0, 8, (num_quantizers, 1))
codes_b2 = torch.randint(0, 8, (num_quantizers, 2))
codes_c1 = torch.randint(0, 8, (num_quantizers, 2))
codes_b3 = torch.randint(0, 8, (num_quantizers, 1))
codes_c2 = torch.randint(0, 8, (num_quantizers, 1))

# First call reserves 3 fixed decoder slots for A and B.
out_ab0 = model.batch_decode(
    [codes_a0, codes_b0],
    streaming=True,
    max_batch_size=3,
    reset_stream=True,
)

# Same logical rows continue in-order; C is a tail append.
out_abc1 = model.batch_decode(
    [codes_a1, codes_b1, codes_c0],
    streaming=True,
)

# Finalize A against the pre-call logical order. A still decodes in this call,
# then is evicted immediately afterward.
out_abc2 = model.batch_decode(
    [codes_a2, codes_b2, codes_c1],
    streaming=True,
    finalize_indices=[0],
)

# The next call can shrink to the surviving logical rows only.
out_bc3 = model.batch_decode(
    [codes_b3, codes_c2],
    streaming=True,
)
```

## Repository layout

- `configuration_moss_audio_tokenizer.py`
- `modeling_moss_audio_tokenizer.py`
- `__init__.py`
- `config.json`
- model weights


## Citation
If you use this code or result in your paper, please cite our work as:
```tex

```