Unleashing the Potential of Multimodal LLMs for Zero-Shot
  Spatio-Temporal Video Grounding
Authors: name: Zaiquan Yang; name: Yuhao Liu; name: Gerhard Hancke; name: Rynson W. H. Lau
Published: 2025-09-18 17:35:50

Abstract: Spatio-temporal video grounding (STVG) aims at localizing the spatio-temporal
tube of a video, as specified by the input text query. In this paper, we
utilize multimodal large language models (MLLMs) to explore a zero-shot
solution in STVG. We reveal two key insights about MLLMs: (1) MLLMs tend to
dynamically assign special tokens, referred to as grounding tokens,
for grounding the text query; and (2) MLLMs often suffer from suboptimal
grounding due to the inability to fully integrate the cues in the text query
(e.g., attributes, actions) for inference. Based on these insights, we
propose a MLLM-based zero-shot framework for STVG, which includes novel
decomposed spatio-temporal highlighting (DSTH) and temporal-augmented
assembling (TAS) strategies to unleash the reasoning ability of MLLMs. The DSTH
strategy first decouples the original query into attribute and action
sub-queries for inquiring the existence of the target both spatially and
temporally. It then uses a novel logit-guided re-attention (LRA) module to
learn latent variables as spatial and temporal prompts, by regularizing token
predictions for each sub-query. These prompts highlight attribute and action
cues, respectively, directing the model's attention to reliable spatial and
temporal related visual regions. In addition, as the spatial grounding by the
attribute sub-query should be temporally consistent, we introduce the TAS
strategy to assemble the predictions using the original video frames and the
temporal-augmented frames as inputs to help improve temporal consistency. We
evaluate our method on various MLLMs, and show that it outperforms SOTA methods
on three common STVG benchmarks.
  The code will be available at https://github.com/zaiquanyang/LLaVA_Next_STVG.