Physics-Aware Video Generation via Agentic Planning and Graph-Guided Optimization
Video diffusion models (VDMs) have demonstrated remarkable capabilities in synthesizing high-fidelity, photorealistic video content. However, they fundamentally lack an intrinsic understanding of physical laws and frequently produce visually appealing but causally illogical sequences characterized by structural hallucinations and physically implausible dynamics. Injecting physical awareness via training-free test-time optimization is a promising alternative, yet existing methods rely on global gradient updates and rigid scheduling heuristics that inadvertently corrupt passive backgrounds and fail to model complex dynamic state changes. To address this, we propose PhysPlan, a novel training-free guidance framework that shifts the paradigm from stochastic visual interpolation to agentic physics simulation. First, a VLM operates as an iterative cognitive simulator, decomposing multimodal inputs into a Chain-of-Visual-Thought to create a multimodal representation of kinematic trajectories and 3D depth geometries. Second, these signals drives an object-centric test-time optimization. Unlike prior training-free methods that rely on global gradients and rigid scheduling heuristics, PhysPlan introduces Object-Centric Gradient Routing to isolate kinematic modifications and completely lock the passive environment. Furthermore, our Kinetic Intensity Profiling dynamically parameterizes framework hyperparameters to accommodate the varying severity of physical deformations. Extensive evaluations on the PhyGenBench and Physics-IQ benchmarks demonstrate that PhysPlan significantly outperforms both foundational and controllable VDM baselines, offering a promising approach for improving the physical understanding of video generation.