Backtrace Mamba: Reviving Critical Temporal Contexts via Hierarchical Memory Compression for Online Action Detection

Online Action Detection (OAD) requires real-time prediction of ongoing actions without access to future frames, posing challenges in balancing computational efficiency and long-term dependencies modeling.Existing methods either suffer from slow training and limited temporal receptive fields, or face high computational costs and delayed inference, lacking the capability to tackle extra-long video inputs. Thus, we present a novel Mamba-based OAD framework (MOAD) that efficiently and effectively performs OAD.The hierarchical memory mechanism is introduced to intelligently store high-value scene and action frames based on motion-aware similarity metrics, preserving essential historical knowledge in an online manner. To further reduce storage space, we design a memory quantization method to compress the stored historical features. Additionally, the temporal soft pruning strategy built upon the memory bank is proposed to dynamically remove redundant features, reducing temporal redundancy while maintaining temporal coherence. Sufficient experiments on four challenging benchmarks prove our method significantly outperforms existing methods.