Re-thinking Temporal Search for Long-Form Video Understanding

Efficient understanding of long-form videos remains a significant challenge in computer vision. In this work, we revisit temporal search paradigms for long-form video understanding, studying a fundamental issue pertaining to all state-of-the-art (SOTA) long-context vision-language models (VLMs). In particular, our contributions are two-fold: **First**, we formulate temporal search as a **Long Video Haystack** problem, i.e., finding a minimal set of relevant frames (typically one to five) among tens of thousands of frames from real-world long videos given specific queries. To validate our formulation, we create **LV-Haystack**, the first benchmark containing 3,874 human-annotated instances with fine-grained evaluation metrics for assessing keyframe search quality and computational efficiency. Experimental results on LV-Haystack highlight a significant research gap in temporal search capabilities, with SOTA keyframe selection methods achieving only 2.1% temporal F1 score on the LVBench subset.**Next**, inspired by visual search in images, we re-think temporal searching and propose a lightweight keyframe searching framework, $T^*$ , which casts the expensive temporal search as a spatial search problem. $T^*$ leverages superior visual localization capabilities typically used in images and introduces an adaptive zooming-in mechanism that operates across both temporal and spatial dimensions. Our extensive experiments show that when integrated with existing methods, $T^*$ significantly improves SOTA long-form video understanding performance. Specifically, under an inference budget of 32 frames, $T^*$ improves GPT-4o's performance from 50.5% to **53.1%** and LLaVA-OneVision-72B's performance from 56.5% to **62.4%** on LongVideoBench XL subset. Our PyTorch code, benchmark dataset and models are included in the Supplementary material.