LibraGen: Playing a Balance Game in Subject-Driven Video Generation

TL;DR

LibraGen introduces a balanced approach to subject-driven video generation by harmonizing intrinsic model priors with new S2V capabilities through data quality emphasis, post-training tuning, and dynamic guidance, achieving superior results.

Contribution

The paper presents LibraGen, a novel framework that balances foundation model strengths and S2V capabilities via a quality-focused pipeline, post-training tuning, and dynamic inference control.

Findings

Outperforms existing S2V models with limited data

Effective balance between motion coherence and prompt alignment

Demonstrates superior qualitative and quantitative results

Abstract

With the advancement of video generation foundation models (VGFMs), customized generation, particularly subject-to-video (S2V), has attracted growing attention. However, a key challenge lies in balancing the intrinsic priors of a VGFM, such as motion coherence, visual aesthetics, and prompt alignment, with its newly derived S2V capability. Existing methods often neglect this balance by enhancing one aspect at the expense of others. To address this, we propose LibraGen, a novel framework that views extending foundation models for S2V generation as a balance game between intrinsic VGFM strengths and S2V capability. Specifically, guided by the core philosophy of "Raising the Fulcrum, Tuning to Balance," we identify data quality as the fulcrum and advocate a quality-over-quantity approach. We construct a hybrid pipeline that combines automated and manual data filtering to improve overall data quality. To further harmonize the VGFM's native capabilities with its S2V extension, we introduce a Tune-to-Balance post-training paradigm. During supervised fine-tuning, both cross-pair and in-pair data are incorporated, and model merging is employed to achieve an effective trade-off. Subsequently, two tailored direct preference optimization (DPO) pipelines, namely Consis-DPO and Real-Fake DPO, are designed and merged to consolidate this balance. During inference, we introduce a time-dependent dynamic classifier-free guidance scheme to enable flexible and fine-grained control. Experimental results demonstrate that LibraGen outperforms both open-source and commercial S2V models using only thousand-scale training data.