  Large language models (LLMs) have shown remarkable text understanding
capabilities, which have been extended as Video LLMs to handle video data for
comprehending visual details. However, existing Video LLMs can only provide a
coarse description of the entire video, failing to capture the precise start
and end time boundary of specific events. In this paper, we solve this issue
via proposing VTimeLLM, a novel Video LLM designed for fine-grained video
moment understanding and reasoning with respect to time boundary. Specifically,
our VTimeLLM adopts a boundary-aware three-stage training strategy, which
respectively utilizes image-text pairs for feature alignment, multiple-event
videos to increase temporal-boundary awareness, and high-quality
video-instruction tuning to further improve temporal understanding ability as
well as align with human intents. Extensive experiments demonstrate that in
fine-grained time-related comprehension tasks for videos such as Temporal Video
Grounding and Dense Video Captioning, VTimeLLM significantly outperforms
existing Video LLMs. Besides, benefits from the fine-grained temporal
understanding of the videos further enable VTimeLLM to beat existing Video LLMs
in video dialogue benchmark, showing its superior cross-modal understanding and
reasoning abilities.
