---
language: en
tags:
  - vla
  - tokenizer
  - robotics
  - multimodal
  - pose-estimation
  - audio
license: apache-2.0
---

# VLA Tokenizer — Adaptive v2 (GPT-NeoX-20b + SNAC)

Extended GPT-NeoX-20b tokenizer for the **FineVideo-VLA** multimodal dataset.
Adds 3D human pose tokens, video tokens, and SNAC audio tokens on top of the
[EleutherAI/gpt-neox-20b](https://huggingface.co/EleutherAI/gpt-neox-20b) base.

**Vocab size: 156,505** (50,277 base + 93,938 VLA + 12,290 SNAC)

> **v1 → v2 change:** Added 12,290 SNAC audio tokens (`<snac>`, `</snac>`,
> and 12,288 `<snac_N>` tokens) for the SNAC listen format used in
> [MixtureVitae-Omni](https://huggingface.co/datasets/mixture-vitae/MixtureVitae-Omni)
> and FineVideo-VLA audio tokenization. All existing v1 token IDs are unchanged.

---

## Token categories

| Category | Format | Count | Notes |
|----------|--------|-------|-------|
| Seed2 visual | `<seed2_N>` (N: 0–8191) | 8,192 | Semantic keyframe tokens, 1 FPS |
| Cosmos spatial | `<cosmos_N>` (N: 0–63999) | 64,000 | Spatial video tokens, every 8 frames |
| AVC-LM H.264 | `<avclm_N>` (N: 0–8191) | 8,192 | H.264 BPE tokens, every 8 frames |
| Agent legacy | `<agent_N>` (N: 0–255) | 256 | Legacy opaque agent tokens |
| FPS prefix | `<fps_N>` (N: 1–60) | 60 | Frame rate marker per chunk |
| Joint position | `<{joint}_x/y/z_N>` (N: 0–255) | 13,056 | Quantized xyz, maps [-2m, +2m] |
| Joint time | `<{joint}_t_N>` (N: 0–7) | 136 | Frame index within 8-frame window |
| Modality wrappers | `<seed2>`, `</agent>`, etc. | 46 | Open/close tags + joint wrappers |
| **SNAC Level 0** | `<snac_128266>` – `<snac_132361>` | 4,096 | 12.5 Hz coarse audio |
| **SNAC Level 1 even** | `<snac_132362>` – `<snac_136457>` | 4,096 | 25 Hz fine audio (even frames) |
| **SNAC Level 1 odd** | `<snac_144650>` – `<snac_148745>` | 4,096 | 25 Hz fine audio (odd frames) |
| **SNAC wrappers** | `<snac>`, `</snac>` | 2 | Block delimiters |

**Total new tokens: 106,228** (93,938 VLA + 12,290 SNAC)

---

## 17 Named Joints (H36M skeleton)

`pelvis` · `r_hip` · `r_knee` · `r_ankle` · `l_hip` · `l_knee` · `l_ankle` ·
`spine` · `thorax` · `nose` · `head_top` · `l_shoulder` · `l_elbow` · `l_wrist` ·
`r_shoulder` · `r_elbow` · `r_wrist`

---

## Token format in context

Each 8-frame chunk in the interleaved sequence looks like:

```
<cosmos_63127> <cosmos_42647> ... </cosmos>
<avc_lm> <avclm_263> <avclm_107> ... </avc_lm>
<agent>
  <fps_30>
  <pelvis> <pelvis_t_0> <pelvis_x_128> <pelvis_y_128> <pelvis_z_128>
           <pelvis_t_7> <pelvis_x_129> <pelvis_y_128> <pelvis_z_128> </pelvis>
  <r_hip>  <r_hip_t_0>  <r_hip_x_115>  ...  </r_hip>
  ... 17 joints total ...
</agent>
<snac> <snac_131580> <snac_134777> <snac_147244>
       <snac_131267> <snac_135192> <snac_148152>
       <snac_128995> <snac_133704> <snac_145875> </snac>
```

SNAC listen format: 3 tokens per base frame (L0 + L1_even + L1_odd),
37.5 tokens/sec, ~9–10 tokens per 8-frame chunk at 30 FPS.

---

## Usage

```python
from transformers import AutoTokenizer

tok = AutoTokenizer.from_pretrained("EmpathicRobotics/tokenizer-vla-adaptive-v2")
print(len(tok))  # 156505

# All VLA and SNAC tokens are single atomic tokens
print(tok.encode("<seed2_1137>",   add_special_tokens=False))  # [59908]
print(tok.encode("<pelvis_x_128>", add_special_tokens=False))  # [131151]
print(tok.encode("<fps_30>",       add_special_tokens=False))  # [130992]
print(tok.encode("<snac_128266>",  add_special_tokens=False))  # single ID
print(tok.encode("<snac_132362>",  add_special_tokens=False))  # single ID
print(tok.encode("<snac_144650>",  add_special_tokens=False))  # single ID
```

---

## How it was created

```python
from transformers import AutoTokenizer

# Start from existing v1 tokenizer (144,215 vocab)
tok = AutoTokenizer.from_pretrained("EmpathicRobotics/tokenizer-vla-adaptive")

snac_tokens = ["<snac>", "</snac>"]
snac_tokens += [f"<snac_{i + 128266}>" for i in range(4096)]  # L0
snac_tokens += [f"<snac_{i + 132362}>" for i in range(4096)]  # L1 even
snac_tokens += [f"<snac_{i + 144650}>" for i in range(4096)]  # L1 odd

tok.add_tokens(snac_tokens, special_tokens=True)  # all atomic
tok.save_pretrained("tokenizer-vla-adaptive-v2")
# vocab size: 156,505
```

Script: `tools/build_tokenizers.py` in the
[finevideo-vla](https://github.com/TieuDaoChanNhan/finevideo-vla) repo.

---

## Related

| Resource | Link |
|----------|------|
| v1 tokenizer (no SNAC) | [tokenizer-vla-adaptive](https://huggingface.co/EmpathicRobotics/tokenizer-vla-adaptive) |
| Qwen3-based version | [tokenizer-vla-qwen3](https://huggingface.co/EmpathicRobotics/tokenizer-vla-qwen3) |
| VLA model trained with v1 | [vla-1.7b-pab-spline-adaptive](https://huggingface.co/EmpathicRobotics/vla-1.7b-pab-spline-adaptive) |
| FineVideo-VLA dataset | [FineVideo-Phase7-Flattened](https://huggingface.co/datasets/EmpathicRobotics/FineVideo-Phase7-Flattened) |