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Ultra Flash: Scaling Real-Time Streaming Video Generation to High Resolutions

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# ⚡ Ultra Flash

**Scaling Real-Time Streaming Video Generation to High Resolutions**

**1K video at ~30 FPS &nbsp;·&nbsp; 2K video at ~18 FPS &nbsp;·&nbsp; single GPU**

</div>

**Ultra Flash** is the first framework to achieve **real-time high-resolution streaming video generation**, producing **1K video at ~30 FPS** and **2K video at ~18 FPS** on a single GPU. It cascades three key components after a low-resolution streaming generator:

1. 🎯 **Architecture-Preserving T2V-to-TV2V SR Training** with AIGC-oriented degradation
2. 🪶 **Causal Streaming Latent Upsampler** (~2M params, <5% overhead)
3. 🚄 **Cascaded Streaming Optimization** (sparse distillation + DPO + dynamic cache management)

---

### 📰 News

- **Aug 2026 — Inference code and checkpoints released** on GitHub and
  [Hugging Face](https://huggingface.co/xin1u/UltraFlash). 🎉

---

### 📋 TODO

- ✅ Release inference code and checkpoints (short + long video)
- ⬜ Release training code and configs

---

### 🔧 Requirements

- NVIDIA GPU with **24+ GB** memory (RTX 4090, H200, B200 tested)
- Linux operating system
- 64 GB RAM
- Python 3.10+

---

### 🚀 Getting Started

#### 1️⃣ Installation

```bash
conda create -n ultraflash python=3.10 -y
conda activate ultraflash
cd inference
pip install -r requirements.txt
pip install flash-attn --no-build-isolation

# Block Sparse Attention (CUDA kernel, required for SR DiT)
git clone https://github.com/mit-han-lab/Block-Sparse-Attention.git
cd Block-Sparse-Attention
pip install -e .
cd ..

python setup.py develop
```

#### 2️⃣ Download Checkpoints

```bash
# Wan2.1-T2V-1.3B base model
huggingface-cli download Wan-AI/Wan2.1-T2V-1.3B --local-dir inference/wan_models/Wan2.1-T2V-1.3B

# Ultra Flash checkpoints (short video)
huggingface-cli download xin1u/UltraFlash --local-dir inference/checkpoints

# Ultra Flash checkpoints (long video, optional)
huggingface-cli download xin1u/UltraFlash-Long --local-dir inference_long/checkpoints

# Symlink shared checkpoints to avoid duplication (optional)
cd inference_long/checkpoints
ln -s ../../inference/checkpoints/sr_dit_sparse.pth .
ln -s ../../inference/checkpoints/latent_upsampler.pth .
ln -s ../../inference/checkpoints/tiny_decoder.pth .
ln -s ../../inference/checkpoints/ultra_decoder_v3.pth .
ln -s ../../inference/wan_models wan_models
```

The `inference/checkpoints/` folder should contain:

| File | Description |
|------|-------------|
| `self_forcing_dmd.pt` | Self-Forcing 4-step streaming generator |
| `sr_dit_sparse.pth` | Sparse causal SR DiT (single-step) |
| `latent_upsampler.pth` | Causal streaming latent upsampler |
| `tiny_decoder.pth` | Tiny Decoder for high-resolution decoding |
| `ultra_decoder_v3.pth` | **(Optional)** Ultra Decoder V3 — improved HR decoder with better texture fidelity |

#### 3️⃣ Quick Start

**One-click inference (2K or 1K):**

```bash
cd inference
bash inference.sh
```

**Custom inference:**

```bash
cd inference
python inference.py \
    --config_path configs/self_forcing_dmd_4step.yaml \
    --checkpoint_path checkpoints/self_forcing_dmd.pt \
    --data_path prompts/examples.txt \
    --output_folder outputs/ \
    --use_ema \
    --tiny_decoder \
    --torch_compile \
    --compile_sr_dit
```

**LR-only mode (480P, for comparison):**

---

### 🎬 Long Video Generation

The `inference_long/` directory supports long video generation (~10 seconds, 120 latent frames) using **LongLive** with LoRA adapters and the same SR cascade pipeline.

#### Additional checkpoints for long video

The `inference_long/checkpoints/` folder requires:

| File | Description |
|------|-------------|
| `longlive_base.pt` | LongLive base generator (Self-Forcing + long video fine-tuning) |
| `lora.pt` | LoRA adapter for long video coherence (rank 256) |
| `sr_dit_sparse.pth` | Same as `inference/` — can be symlinked |
| `latent_upsampler.pth` | Same as `inference/` — can be symlinked |
| `tiny_decoder.pth` | Same as `inference/` — can be symlinked |

#### Run long video inference

```bash
cd inference_long
python inference_sr.py \
    --config_path configs/longlive_inference_sr.yaml \
    --use_sparse_sr \
    --tiny_decoder \
    --torch_compile \
    --compile_sr_dit
```

---

### ⚙️ Key Arguments

#### Short video (`inference/inference.py`)

| Argument | Default | Description |
|----------|---------|-------------|
| `--use_ema` | False | Load EMA weights (recommended) |
| `--num_output_frames` | 21 | Number of latent frames (~5s video at 21 frames) |
| `--num_samples` | 1 | Number of samples per prompt |
| `--seed` | 0 | Random seed |
| `--torch_compile` | False | Enable torch.compile for SF DiT (~1.5x speedup) |
| `--compile_sr_dit` | False | Enable torch.compile for SR DiT |
| `--fp8` | False | FP8 quantization for SF DiT |
| `--tiny_decoder` | True | Use Tiny Decoder for HR decoding (faster than Wan VAE) |
| `--decoder_ckpt` | `checkpoints/tiny_decoder.pth` | Path to decoder checkpoint |
| `--ultra_decoder_v3` | False | Use Ultra Decoder V3 (better texture, replaces Tiny Decoder) |
| `--ultra_decoder_v3_ckpt` | `checkpoints/ultra_decoder_v3.pth` | Path to V3 decoder checkpoint |
| `--sr_kv_len` | 3 | SR DiT KV cache window length |
| `--condition_noise_scale` | 0.0 | Noise injected into SR condition |
| `--save_lr_video` | False | Also save LR video output |
| `--lr_only` | False | Only generate LR video (skip SR cascade) |
| `--dcm_lr_steps_subsequent` | 4 | Denoising steps for subsequent chunks (4=full) |
| `--dcm_adaptive_refresh` | False | Enable IQA-based adaptive cache refresh |
| `--no_dcm` | False | Disable all DCM optimizations |

#### Long video (`inference_long/inference_sr.py`)

Inherits most arguments from the YAML config. Key CLI overrides:

| Argument | Default | Description |
|----------|---------|-------------|
| `--config_path` | (required) | Path to YAML config (e.g. `configs/longlive_inference_sr.yaml`) |
| `--use_sparse_sr` | False | Use sparse attention for SR DiT (recommended) |
| `--tiny_decoder` | False | Use Tiny Decoder for HR decoding |
| `--torch_compile` | False | Compile SF DiT |
| `--compile_sr_dit` | False | Compile SR DiT |
| `--fp8` | False | FP8 quantization for SF DiT |
| `--fp8_sr` | False | FP8 quantization for SR DiT |

---

### 🧠 Dynamic Cache Management (DCM)

Ultra Flash introduces three inference-time optimizations:

| Optimization | Effect | Quality Impact |
|---|---|---|
| **(i) LR Step Reduction** | Saves 1 forward pass per chunk | Negligible |
| **(ii) Adaptive Cache Refresh** | Skips context rerun when quality is sufficient | Negligible |
| **(iii) SR Cache Adaptation** | Reduces SR KV cache memory over time | Minimal |

---

### 🏗️ Architecture

```
Text Prompt
    │
    ▼
┌─────────────────────────┐
│  Self-Forcing Generator  │  480P, 4 denoising steps, streaming
│  (Wan2.1-1.3B causal)    │
└───────────┬─────────────┘
            │ LR latents (16×60×104)
            ▼
┌─────────────────────────┐
│  Causal Latent Upsampler │  2× or 3× spatial upsampling in latent space
│  (~2M params, Conv2D)    │  Causal memory for temporal coherence
└───────────┬─────────────┘
            │ HR latents (16×120×208)
            ▼
┌─────────────────────────┐
│  Sparse SR DiT           │  Single-step denoising, block-sparse attention
│  (1.3B, causal)          │  Adaptive top-k with local window
└───────────┬─────────────┘
            │ Refined HR latents
            ▼
┌─────────────────────────┐
│  Tiny Decoder (HR)       │  Latent → Pixel (960×1664 or 1440×2496)
│  (Causal Memory Network) │  Sequential streaming mode
└───────────┬─────────────┘
            │
            ▼
       2K Video Output (~18 FPS)
```

---

### 🏋️ Training

Training code is coming soon. See the `train/` directory for updates.

---

### 🤗 Acknowledgements

This work builds upon the following excellent open-source projects:

- [FlashVSR](https://github.com/OpenImagingLab/FlashVSR) — Block-sparse attention for streaming video super-resolution
- [Self-Forcing](https://github.com/guandeh17/Self-Forcing) — Real-time autoregressive video generation with self-rollout training
- [TAEHV](https://github.com/madebyollin/taehv) — Tiny Autoencoder for high-resolution video decoding
- [Wan2.1](https://github.com/Wan-Video/Wan2.1) — Video DiT foundation model

We thank the authors for their outstanding contributions to the community.

---

### 📞 Contact

Please feel free to contact us if there is any question (luxion@mail.ustc.edu.cn).

---

### 📜 Citation

```bibtex
@inproceedings{luxury2026ultraflash,
  title={Ultra Flash: Scaling Real-Time Streaming Video Generation to High Resolutions},
  author={Luxury and Huang, Jie and Fan, Zihao and Ma, Xiaoxiao and Li, Yuming and Zhuang, Jun-hao and Xue, Zeyue and Fu, Siming and Li, Haoran and Zhong, Mingchen and Zhang, Guohui and Ma, Shichen and Liu, Yijun and Shi, Jiaqi and Ma, Yanwen and Su, Yaofeng and Wang, Haoyu and Li, Yaowei and Zhang, Songchun and Jin, Weiyang and Bian, Yuxuan and Zhang, Shiyi and Xu, Haojun and Lu, Shuai and Han, Xin and Tang, Wei and Huang, Haoyang and Duan, Nan},
  booktitle={arXiv preprint},
  year={2026}
}
```

---

### 📄 License

This project is released under the [Apache 2.0 License](inference/LICENSE).

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