AVSCap: Orchestrating Audio-Visual Synergy for Omni-modal Video Captioning

Yanghai Wang, Jiahao Wang, Jiafu Tang, Yuanxing Zhang, Zhe Cao, Hanyan Bian, Zijie Zhang, Weiliang Luo, Zhiyu Pan, Zixuan Dong, Jiaheng Liu, Zhaoxiang Zhang


Abstract
Omni-modal video captioning is not merely combining visual captioning with audio transcription: a useful caption must describe how visual actions, speech, music, and sound effects co-evolve over time. Existing large multimodal models often fail at this relational step, treating audio and visual streams as loosely coupled observations, relying heavily on automatic speech recognition, and under-specifying non-speech sounds and their links to visual events. We present AVSCap, a framework for audio-visual captioning centered on explicit cross-modal event binding. First, we construct AVSCap-130K, a tri-modal training corpus generated by a decoupled-then-fused pipeline that anchors visual and acoustic evidence independently before composing temporally grounded omni-modal captions. Second, we train AVSCap-7B, a 7B captioner with a two-stage strategy: supervised fine-tuning establishes baseline captioning ability, while a sample-efficient reinforcement learning stage uses hybrid rewards to optimize acoustic completeness and audio-visual synergy. Our scaling analysis shows that reinforcement learning brings larger gains than simply increasing SFT data. Third, we introduce AVSCapBench, a human-curated benchmark that decomposes captions into visual, audio, and synergy events and evaluates them with fine-grained event recall. Experiments on AVSCapBench and external benchmarks show that AVSCap-7B improves non-speech audio coverage and cross-modal binding, delivering the best overall performance among evaluated open-source models.
Anthology ID:
2026.emnlp-main.1433
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
32731–32761
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1433/
DOI:
Bibkey:
Cite (ACL):
Yanghai Wang, Jiahao Wang, Jiafu Tang, Yuanxing Zhang, Zhe Cao, Hanyan Bian, Zijie Zhang, Weiliang Luo, Zhiyu Pan, Zixuan Dong, Jiaheng Liu, and Zhaoxiang Zhang. 2026. AVSCap: Orchestrating Audio-Visual Synergy for Omni-modal Video Captioning. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 32731–32761, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
AVSCap: Orchestrating Audio-Visual Synergy for Omni-modal Video Captioning (Wang et al., EMNLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.emnlp-main.1433.pdf