1. Introduction
In recent years, UAV swarm has raised a lot of research interests due to its wide applications, as well as challenges and characteristics in system complexity, flexibility and scalability, and robustness [21]. As a crucial step for drones to emerge intelligence, smart perception of the environment heavily relies on UAV vision. Multi-object tracking (MOT) – identify and track object instances in video sequences – is one of the most critical functions of UAV vision.