DynamicRad: Content-Adaptive Sparse Attention for Long Video Diffusion

Leveraging the natural spatiotemporal energy decay in video diffusion offers a path to efficiency, yet relying solely on rigid static masks risks losing critical long-range information in complex dynamics. To address this issue, we propose DynamicRad, a unified sparse-attention paradigm that grounds adaptive selection within a radial locality prior. DynamicRad introduces a dual-mode strategy: textitstatic-ratio for speed-optimized execution and textitdynamic-threshold for quality-first filtering. To ensure robustness without online search overhead, we integrate an offline Bayesian Optimization (BO) pipeline coupled with a semantic motion router. This lightweight projection module maps prompt embeddings to optimal sparsity regimes with minimal runtime overhead. Unlike online profiling methods, our offline BO optimizes attention reconstruction error (MSE) on a physics-based proxy task, ensuring rapid convergence. Experiments on HunyuanVideo and Wan2.1-14B demonstrate that DynamicRad pushes the efficiency--quality Pareto frontier, achieving 1.7×--2.5× inference speedups with over 80% effective sparsity. In some long-sequence settings, the dynamic mode even matches or exceeds the dense baseline, while mask-aware LoRA further improves long-horizon coherence. Code is available at https://github.com/Adamlong3/DynamicRad.