  We present LLoVi, a language-based framework for long-range video
question-answering (LVQA). Unlike prior long-range video understanding methods,
which are often costly and require specialized long-range video modeling design
(e.g., memory queues, state-space layers, etc.), our approach uses a
frame/clip-level visual captioner (e.g., BLIP2, LaViLa, LLaVA) coupled with a
Large Language Model (GPT-3.5, GPT-4) leading to a simple yet surprisingly
effective LVQA framework. Specifically, we decompose short and long-range
modeling aspects of LVQA into two stages. First, we use a short-term visual
captioner to generate textual descriptions of short video clips (0.5-8s in
length) densely sampled from a long input video. Afterward, an LLM aggregates
the densely extracted short-term captions to perform long-range temporal
reasoning needed to understand the whole video and answer a question. To
analyze what makes our simple framework so effective, we thoroughly evaluate
various components of our system. Our empirical analysis reveals that the
choice of the visual captioner and LLM is critical for good LVQA performance.
Furthermore, we show that a specialized prompt that asks the LLM first to
summarize the noisy short-term visual captions and then answer a given input
question leads to a significant LVQA performance boost. On EgoSchema, which is
best known as a very long-form video question-answering benchmark, our method
achieves 50.3% accuracy, outperforming the previous best-performing approach by
18.1% (absolute gain). In addition, our approach outperforms the previous
state-of-the-art by 4.1% and 3.1% on NeXT-QA and IntentQA. We also extend LLoVi
to grounded LVQA and show that it outperforms all prior methods on the NeXT-GQA
dataset. We will release our code at https://github.com/CeeZh/LLoVi.
