ResearchResearch paperLarge Language Models · Multimodal Models1 source · Oct 18, 2026

From Label Priors to Task Evidence: Efficient Long-Video Frame Selection via Bayesian GRPO

Multimodal Large Language Models (MLLMs) face significant scalability challenges in long-video understanding due to quadratic attention complexity and context window constraints.

Key points

  • Existing retrieval-based approaches typically rely on supervised learning from static keyframe annotations.
  • To bridge this gap, we propose a probabilistic framework that reformulates frame selection as latent-variable inference.
  • Then, we treat a frozen MLLM as a task environment and use its answer likelihood as dense task evidence to refine the policy via Bayesian Group Relative Policy Optimization (GRPO).
  • Extensive experiments on Video-MME, MLVU, and LongVideoBench demonstrate that our selector achieves competitive accuracy with MLLM-based scorers while retaining the inference efficiency of lightweight methods.

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