SolitaryThinker 49a13e6359 [skill] Add add-model and review-add-model-pr skills
Two skills split out of the will/stable-audio PR (#1260) so the model
work and the agent infra evolve on independent review cycles.

`add-model/SKILL.md` (~1600 lines) — the canonical procedure for
porting a new diffusion model into FastVideo, distilled from the Wan,
LTX-2, Hunyuan, Cosmos, Stable Audio, and MagiHuman ports. Covers the
17-row Files-table, 16-step procedure, FastVideo layer/attention
selection rules, parity-test pattern, weight conversion recipe, and
the I2V variant pattern.

`add-model/REVIEW.md` (~1900 lines) — 36 documented failure modes
discovered while porting / re-reviewing those families. Each item is
a self-contained "what we did wrong, what to do instead" entry with a
suggested action on the skill text. Items 1-22 from the Wan / MagiHuman
porting passes; items 23-36 from the Stable Audio port (audio as
first-class workload, hard ban on `from diffusers import` for model
classes at runtime, user-story example docstrings, single-class
kwargs-driven variants, examples accept paths not user-written decode
glue, etc.).

`add-model/add_model_split.md` — plan for breaking the monolithic
1600-line SKILL.md into ~12 satellite docs (deferred until after
the next porting pass validates which sections are most-referenced).

`review-add-model-pr/SKILL.md` (~480 lines, NEW) — reviewer-facing
dual of `add-model`. Walks a PR reviewer through the canonical
surface (per-component checklist for DiT / VAE / encoder /
PipelineConfig / pipeline class / stages / presets+registry / tests /
example), indexes the 36 REVIEW failure modes by where they show up
in a diff (the "Pitfall map"), and produces a structured verdict
(block / nit / follow-up) with a copy-pasteable comment skeleton.
Key design choice: the reviewer's job is NOT to redesign the port,
just to verify the porter followed the canonical procedure honestly
and exercised the parity gate — REVIEW item 16 ("skip-on-missing
parity is a silent no-op trap") gets disproportionate weight because
it's the single most expensive failure mode in past ports.

Both skills registered in `.agents/skills/index.jsonl` as
`status: draft, trust: low` per existing convention.
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| Documentation | Quick Start | Weekly Dev Meeting | 🟣💬 Slack | 🟣💬 WeChat |

FastVideo is a unified post-training and real-time inference framework for accelerated video generation.

NEWS

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Key Features

FastVideo has the following features:

  • End-to-end post-training support for bidirectional and autoregressive models:
    • Support full finetuning and LoRA finetuning for state-of-the-art open video DiTs
    • Data preprocessing pipeline for video, image, and text data
    • Distribution Matching Distillation (DMD2) stepwise distillation.
    • Sparse attention with Video Sparse Attention
    • Sparse distillation to achieve >50x denoising speedup
    • Scalable training with FSDP2, sequence parallelism, and selective activation checkpointing.
    • Causal distillation through Self-Forcing
    • See this page for full list of supported models and recipes.
  • State-of-the-art performance optimizations for inference
    • Sequence Parallelism for distributed inference
    • Multiple state-of-the-art attention backends
    • User-friendly CLI and Python API
    • See this page for full list of supported optimizations.
  • Diverse hardware and OS support
    • Support H100, A100, 4090
    • Support Linux, Windows, MacOS
    • See this page for full list of supported models, hardware assumptions, and optimization compatibility.

Getting Started

We recommend using uv to create a clean environment. If you previously used Conda, switching to uv generally gives faster and more stable installs.

# Create and activate a new uv environment
uv venv --python 3.12 --seed
source .venv/bin/activate

# Install FastVideo
uv pip install fastvideo

Please see our docs for more detailed installation instructions.

Sparse Distillation

For our sparse distillation techniques, please see our distillation docs and check out our blog.

See below for recipes and datasets:

Model Sparse Distillation Dataset
FastWan2.1-T2V-1.3B Recipe FastVideo Synthetic Wan2.1 480P
FastWan2.2-TI2V-5B Recipe FastVideo Synthetic Wan2.2 720P

Inference

Generating Your First Video

Here's a minimal example to generate a video using the default settings. Make sure VSA kernels are installed. Create a file called example.py with the following code:

import os
from fastvideo import VideoGenerator

def main():
    os.environ["FASTVIDEO_ATTENTION_BACKEND"] = "VIDEO_SPARSE_ATTN"

    # Create a video generator with a pre-trained model
    generator = VideoGenerator.from_pretrained(
        "FastVideo/FastWan2.1-T2V-1.3B-Diffusers",
        num_gpus=1,  # Adjust based on your hardware
    )

    # Define a prompt for your video
    prompt = "A curious raccoon peers through a vibrant field of yellow sunflowers, its eyes wide with interest."

    # Generate the video
    video = generator.generate_video(
        prompt,
        output_path="my_videos/",  # Controls where videos are saved
        save_video=True
    )

if __name__ == '__main__':
    main()

Run the script with:

python example.py

For a more detailed guide, please see our inference quick start.

Awesome work using FastVideo or our research projects

  • SGLang: SGLang's diffusion inference functionality is based on a fork of FastVideo on Sept. 24, 2025.
  • DanceGRPO: A unified framework to adapt Group Relative Policy Optimization (GRPO) to visual generation paradigms. Code based on FastVideo.
  • SRPO: A method to directly align the full diffusion trajectory with fine-grained human preference. Code based on FastVideo.
  • DCM: Dual-expert consistency model for efficient and high-quality video generation. Code based on FastVideo.
  • HY-WorldPlay: An action-conditioned world model model trained using FastVideo framework.
  • Hunyuan Video 1.5: A leading lightweight video generation model, where they proposed SSTA based on Sliding Tile Attention.
  • Kandinsky-5.0: A family of diffusion models for video & image generation, where their NABLA attention includes a Sliding Tile Attention branch.
  • LongCat Video: A foundational video generation model with 13.6B parameters with block-sparse attention similar to Video Sparse Attention.

🤝 Contributing

We welcome all contributions. Please check out our guide here. See details in development roadmap.

Acknowledgement

We learned the design and reused code from the following projects: Wan-Video, ThunderKittens, DMD2, diffusers, xDiT, vLLM, SGLang. We thank MBZUAI, Anyscale, and GMI Cloud for their support throughout this project.

Citation

If you find FastVideo useful, please consider citing our research work:

@article{zhang2025vsa,
  title={Vsa: Faster video diffusion with trainable sparse attention},
  author={Zhang, Peiyuan and Chen, Yongqi and Huang, Haofeng and Lin, Will and Liu, Zhengzhong and Stoica, Ion and Xing, Eric and Zhang, Hao},
  journal={arXiv preprint arXiv:2505.13389},
  year={2025}
}

@article{zhang2025fast,
  title={Fast video generation with sliding tile attention},
  author={Zhang, Peiyuan and Chen, Yongqi and Su, Runlong and Ding, Hangliang and Stoica, Ion and Liu, Zhengzhong and Zhang, Hao},
  journal={arXiv preprint arXiv:2502.04507},
  year={2025}
}
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