Streaming video understanding without fixed-length segments, using a large multimodal model's semantics to group events
AspireAI community · arXiv
Existing video step-grounding methods are either offline, needing the whole video up front, or online with fixed-length segments that produce noisy, over-segmented output. Hierarchical Step Decomposition is a training-free online framework built on large multimodal models: it incrementally groups incoming segments into semantically consistent events using an anchor caption continuously validated against the visual stream, then performs zero-shot procedural step classification on those events and selectively refines uncertain predictions by decomposing candidate steps into fine-grained substeps. Working on semantic events rather than every fixed-length segment cuts redundant computation and stabilises predictions. On HT-Step, Ego4D Goal-Step and CrossTask the authors report better step recognition, more accurate temporal localisation and faster inference than state-of-the-art methods. Accepted to WACV 2027.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.