TRACE: Object Motion Editing in Videos with First-Frame Trajectory Guidance

We study object motion editing in videos, where the goal is to change a target object's trajectory while preserving the remaining content of the original video. Many existing trajectory-controlled video editing methods require users to specify frame-wise control signals, such as dense point tracks or bounding boxes, making motion design cumbersome and error-prone, particularly in videos with camera motion. We introduce TRACE, a framework that allows users to specify the desired motion path in the first frame alone. The key challenge is that a path defined in the first-frame coordinate system does not directly determine the object's image-space trajectory in subsequent frames as the camera moves. To address this mismatch, TRACE employs a two-stage pipeline. First, a cross-view motion transformation module converts the first-frame path into frame-aligned bounding-box trajectories. Second, a motion-conditioned video re-synthesis module removes the object from its original trajectory and regenerates it along the transformed trajectory while preserving non-target video content. Experiments on diverse real-world videos show that TRACE produces more coherent and controllable motion edits than recent image-to-video and video-to-video methods