  We propose a Cascaded Buffered IoU (C-BIoU) tracker to track multiple objects
that have irregular motions and indistinguishable appearances. When appearance
features are unreliable and geometric features are confused by irregular
motions, applying conventional Multiple Object Tracking (MOT) methods may
generate unsatisfactory results. To address this issue, our C-BIoU tracker adds
buffers to expand the matching space of detections and tracks, which mitigates
the effect of irregular motions in two aspects: one is to directly match
identical but non-overlapping detections and tracks in adjacent frames, and the
other is to compensate for the motion estimation bias in the matching space. In
addition, to reduce the risk of overexpansion of the matching space, cascaded
matching is employed: first matching alive tracks and detections with a small
buffer, and then matching unmatched tracks and detections with a large buffer.
Despite its simplicity, our C-BIoU tracker works surprisingly well and achieves
state-of-the-art results on MOT datasets that focus on irregular motions and
indistinguishable appearances. Moreover, the C-BIoU tracker is the dominant
component for our 2-nd place solution in the CVPR'22 SoccerNet MOT and ECCV'22
MOTComplex DanceTrack challenges. Finally, we analyze the limitation of our
C-BIoU tracker in ablation studies and discuss its application scope.
