  Although end-to-end multi-object trackers like MOTR enjoy the merits of
simplicity, they suffer from the conflict between detection and association
seriously, resulting in unsatisfactory convergence dynamics. While MOTRv2
partly addresses this problem, it demands an additional detection network for
assistance. In this work, we serve as the first to reveal that this conflict
arises from the unfair label assignment between detect queries and track
queries during training, where these detect queries recognize targets and track
queries associate them. Based on this observation, we propose MOTRv3, which
balances the label assignment process using the developed release-fetch
supervision strategy. In this strategy, labels are first released for detection
and gradually fetched back for association. Besides, another two strategies
named pseudo label distillation and track group denoising are designed to
further improve the supervision for detection and association. Without the
assistance of an extra detection network during inference, MOTRv3 achieves
impressive performance across diverse benchmarks, e.g., MOT17, DanceTrack.
