MMR-V: What's Left Unsaid? A Benchmark for Multimodal Deep Reasoning in
  Videos
Authors: name: Kejian Zhu, name: Zhuoran Jin, name: Hongbang Yuan, name: Jiachun Li, name: Shangqing Tu, name: Pengfei Cao, name: Yubo Chen, name: Kang Liu, name: Jun Zhao

The sequential structure of videos poses a challenge to the ability of
multimodal large language models (MLLMs) to locate multi-frame evidence and
conduct multimodal reasoning. However, existing video benchmarks mainly focus
on understanding tasks, which only require models to match frames mentioned in
the question (hereafter referred to as "question frame") and perceive a few
adjacent frames. To address this gap, we propose MMR-V: A Benchmark for
Multimodal Deep Reasoning in Videos. The benchmark is characterized by the
following features. (1) Long-range, multi-frame reasoning: Models are required
to infer and analyze evidence frames that may be far from the question frame.
(2) Beyond perception: Questions cannot be answered through direct perception
alone but require reasoning over hidden information. (3) Reliability: All tasks
are manually annotated, referencing extensive real-world user understanding to
align with common perceptions. (4) Confusability: Carefully designed distractor
annotation strategies to reduce model shortcuts. MMR-V consists of 317 videos
and 1,257 tasks. Our experiments reveal that current models still struggle with
multi-modal reasoning; even the best-performing model, o4-mini, achieves only
52.5% accuracy. Additionally, current reasoning enhancement strategies
(Chain-of-Thought and scaling test-time compute) bring limited gains. Further
analysis indicates that the CoT demanded for multi-modal reasoning differs from
it in textual reasoning, which partly explains the limited performance gains.
We hope that MMR-V can inspire further research into enhancing multi-modal
reasoning capabilities.