ManuTrace: An HTML-Based Interface for Manually Extracting Movement Trajectory Data From a Video

Tracking the movements of animals provides fundamental insights into behavioral strategies and ecological adaptations. Recent advances in automated video analysis have enabled the extraction of movement trajectories from video recordings. However, effective automated tracking often requires careful adjustment of recording environments and iterative tuning of software parameters, imposing substantial costs in user proficiency and trial-and-error processes before analyzable data can be obtained. In exploratory analyses of pilot or opportunistically recorded videos, rapid extraction of trajectories from a limited number of videos is often more important than throughput, making such setup costs a practical barrier. Here, we introduce ManuTrace, an HTML-based interface for manual extraction of trajectory data from videos. In this tool, users interactively play, pause, and seek videos and record object positions by mouse clicks, with positions in intermediate frames automatically interpolated and the resulting trajectories exported as CSV files for downstream analysis. As a demonstration, we extracted trajectories from videos of termite groups recorded under both natural and tracking-optimized conditions. Automated tools showed highly variable tracking accuracy depending on recording conditions and individual behavior, often requiring substantial manual correction under unfavorable conditions. In contrast, ManuTrace enabled consistent trajectory extraction across recording conditions, processing a 1800-frame video with 12 individuals (21,600 coordinates in total) within 20 min. The software consists of a single HTML file and runs in any modern web browser without installation, allowing use across diverse environments. Owing to its simplicity and portability, ManuTrace complements automated tracking tools as an entry point to trajectory analysis and also provides a useful resource for educational purposes.