---
library_name: transformers
license: cc-by-nc-4.0
pipeline_tag: feature-extraction
tags:
- audio
- codec
---

# X-Codec2 (Transformers-native)

The X-Codec2 model was proposed in [Llasa: Scaling Train-Time and Inference-Time Compute for Llama-based Speech Synthesis](https://huggingface.co/papers/2502.04128).

X-Codec2 is a neural audio codec designed to improve speech synthesis and general audio generation for large language model (LLM) pipelines. It extends the original X-Codec by refining how semantic and acoustic information is integrated and tokenized, enabling efficient and high-fidelity audio representation.

About its architecture:
- **Unified Semantic-Acoustic Tokenization**: X-Codec2 fuses outputs from a semantic encoder (e.g., Wav2Vec2-BERT) and an acoustic encoder into a single embedding, capturing both high-level meaning (e.g., text content, emotion) and low-level audio details (e.g., timbre).
- **Single-Stage Feature Scalar Quantization (FSQ)**: Unlike the multi-layer residual VQ in most approaches (e.g., DAC, EnCodec, X-Codec, Mimi), X-Codec2 uses a single-layer of Feature Scalar Quantization (FSQ) for stability and compatibility with causal, autoregressive LLMs.
- **Transformer-Friendly Design**: The 1D token structure of X-Codec2 naturally aligns with the autoregressive modeling in LLMs like LLaMA, improving training efficiency and downstream compatibility.

This model was contributed by [Eric Bezzam](https://huggingface.co/bezzam) and [Steven Zheng](https://huggingface.co/Steveeeeeeen).
The original modeling code can be found [here](https://huggingface.co/HKUSTAudio/xcodec2/blob/main/modeling_xcodec2.py), while their training code is [here](https://github.com/zhenye234/X-Codec-2.0).


## Setup

X-Codec2 is supported natively in 🤗 Transformers. Until it is part of an official Transformers release, install from source:

```bash
pip install git+https://github.com/huggingface/transformers
```

## Usage example

Here is a quick example of how to encode and decode an audio using this model:

```python
from datasets import Audio, load_dataset
from transformers import AutoFeatureExtractor, AutoModel

model_id = "HKUSTAudio/xcodec2-hf"
model = AutoModel.from_pretrained(model_id, device_map="auto")
feature_extractor = AutoFeatureExtractor.from_pretrained(model_id)

dataset = load_dataset("hf-internal-testing/librispeech_asr_dummy", "clean", split="validation")
dataset = dataset.cast_column("audio", Audio(sampling_rate=feature_extractor.sampling_rate))
audio = dataset[0]["audio"]["array"]
inputs = feature_extractor(audio=audio, sampling_rate=feature_extractor.sampling_rate, return_tensors="pt").to(
    model.device, model.dtype
)
print("Input waveform shape:", inputs["input_values"].shape)
# Input waveform shape: torch.Size([1, 1, 93760])

# encoder and decoder
audio_codes = model.encode(**inputs).audio_codes
print("Audio codes shape:", audio_codes.shape)
# Audio codes shape: torch.Size([1, 1, 293])
audio_values = model.decode(audio_codes).audio_values
print("Audio values shape:", audio_values.shape)
# Audio values shape: torch.Size([1, 1, 93760])

# Equivalently, you can do encoding and decoding in one step
model_output = model(**inputs)
audio_codes = model_output.audio_codes
audio_values = model_output.audio_values
```

### Batch processing

Unlike the original [release](https://huggingface.co/HKUSTAudio/xcodec2), this implementation also supports batched inputs.

```python
from datasets import Audio, load_dataset
from transformers import AutoFeatureExtractor, AutoModel

batch_size = 2
model_id = "HKUSTAudio/xcodec2-hf"
model = AutoModel.from_pretrained(model_id, device_map="auto")
feature_extractor = AutoFeatureExtractor.from_pretrained(model_id)

dataset = load_dataset("hf-internal-testing/librispeech_asr_dummy", "clean", split="validation")
dataset = dataset.cast_column("audio", Audio(sampling_rate=feature_extractor.sampling_rate))
audios = [dataset[i]["audio"]["array"] for i in range(batch_size)]
inputs = feature_extractor(audio=audios, sampling_rate=feature_extractor.sampling_rate, return_tensors="pt").to(
    model.device, model.dtype
)
print("Input waveform shape:", inputs["input_values"].shape)
# Input waveform shape: torch.Size([2, 1, 93760])

# encoder and decoder
encoder_output = model.encode(**inputs)
audio_codes = encoder_output.audio_codes
print("Audio codes shape:", audio_codes.shape)
# Audio codes shape: torch.Size([2, 1, 293])
audio_values = model.decode(audio_codes).audio_values
print("Audio values shape:", audio_values.shape)
# Audio values shape: torch.Size([2, 1, 93760])

# Equivalently, you can do encoding and decoding in one step
model_output = model(**inputs)
audio_codes = model_output.audio_codes
audio_values = model_output.audio_values
```

### Speed-up with `torch.compile`

You can speed up inference with [`torch.compile`](https://pytorch.org/docs/stable/generated/torch.compile.html). The first few calls will be slower due to compilation overhead, but subsequent calls will be faster.

On an A100, we observed a speed-up of ~1.35 for a batch size of 4 ([script](https://gist.github.com/ebezzam/3b79481b5d48d8e35c4ecc582aee0cb3#file-benchmark_torch_compile-py)).

```python
import torch
from datasets import Audio, load_dataset
from transformers import AutoFeatureExtractor, AutoModel

batch_size = 4
model_id = "HKUSTAudio/xcodec2-hf"
model = AutoModel.from_pretrained(model_id, device_map="auto")
feature_extractor = AutoFeatureExtractor.from_pretrained(model_id)

dataset = load_dataset("hf-internal-testing/librispeech_asr_dummy", "clean", split="validation")
dataset = dataset.cast_column("audio", Audio(sampling_rate=feature_extractor.sampling_rate))
audios = [dataset[i]["audio"]["array"] for i in range(batch_size)]
inputs = feature_extractor(
    audio=audios, sampling_rate=feature_extractor.sampling_rate, padding=True, return_tensors="pt"
).to(model.device, model.dtype)

compiled_model = torch.compile(model, fullgraph=True)

# Warmup (includes compilation on first call)
for _ in range(10):
    with torch.inference_mode():
        _ = compiled_model(**inputs)

with torch.inference_mode():
    output = compiled_model(**inputs)
print("Audio values shape:", output.audio_values.shape)
```