Trace Anything: Representing Any Video in 4D via Trajectory Fields

Building 4D video representations to model underlying spacetime constitutes a crucial step toward understanding dynamic scenes, yet there is no consensus on the paradigm: current approaches resort to additional estimators such as depth, flow, or tracking, or to heavy per-scene optimization, making them brittle and hard to generalize. In a video, its atomic unit, the pixel, follows a continuous 3D trajectory that unfolds over time, acting as the atomic primitive of dynamics. Recognizing this, we propose to represent any video as a Trajectory Field: a dense mapping that assigns each pixel in each frame to a parametric 3D trajectory. To this end, we introduce Trace Anything, a neural network that predicts the trajectory field in a feed-forward manner. Specifically, for each video frame, the model outputs a series of control point maps, defining parametric trajectories for each pixel. Together, our representation and model directly construct a 4D video representation in a single forward pass, without additional estimators or global alignment. We develop a synthetic data platform to construct a training dataset and a benchmark for trajectory field estimation. Experiments show that Trace Anything surpasses existing methods or performs competitively on the new benchmark and established point tracking benchmarks, with significant efficiency gains. Moreover, it facilitates downstream applications such as goal-conditioned manipulation, simple motion extrapolation, and spatio-temporal fusion. We will release the code, the model weights, and the data platform.