alibaba-pai / Wan2.2-Fun-Reward-LoRAs

Wan2.2-Fun-Reward-LoRAs

Introduction

We explore the Reward Backpropagation technique ^{1 2} to optimized the generated videos by Wan2.2-Fun for better alignment with human preferences. We provide the following pre-trained models (i.e. LoRAs) along with the training script . You can use these LoRAs to enhance the corresponding base model as a plug-in or train your own reward LoRA.

For more details, please refer to our GitHub repo .

We found that, MPS reward LoRA for the low-noise model converges significantly more slowly than on the other models, and may not deliver satisfactory results. Therefore, for the low-noise model, we recommend using HPSv2.1 reward LoRA.

Demo

Wan2.2-Fun-A14B-InP

The above test prompts are from T2V-CompBench and expanded into detailed prompts by Llama-3.3. Videos are generated with HPSv2.1 Reward LoRA weight 0.5 and MPS Reward LoRA weight 0.5.

Quick Start

Set lora_path along with lora_weight for the low noise reward LoRA, while specifying lora_high_path and lora_high_weight for high noise reward LoRA in examples/wan2.2_fun/predict_t2v.py .

Training

Please refer to README_TRAIN_REWARD.md

Limitations

1. We observe after training to a certain extent, the reward continues to increase, but the quality of the generated videos does not further improve. The model trickly learns some shortcuts (by adding artifacts in the background, i.e., adversarial patches) to increase the reward.
2. Currently, there is still a lack of suitable preference models for video generation. Directly using image preference models cannot evaluate preferences along the temporal dimension (such as dynamism and consistency). Further more, We find using image preference models leads to a decrease in the dynamism of generated videos. Although this can be mitigated by computing the reward using only the first frame of the decoded video, the impact still persists.

Reference

1. Clark, Kevin, et al. "Directly fine-tuning diffusion models on differentiable rewards.". In ICLR 2024.
2. Prabhudesai, Mihir, et al. "Aligning text-to-image diffusion models with reward backpropagation." arXiv preprint arXiv:2310.03739 (2023).