Overview
MotionBrush is a sophisticated spatial control feature integrated within the Runway Gen-2 and Gen-3 Alpha architectures. Historically, generative video models suffered from 'global motion' issues where the entire frame would shift unpredictably. MotionBrush solves this by allowing creators to apply a weighted mask to specific regions of a static image, instructing the latent diffusion model to generate temporal variance only within those localized pixel coordinates. As of 2026, the tool has evolved to support multi-brush layering, allowing for independent motion vectors (directional, proximity, and scale) within a single generation. It utilizes a dedicated optical flow estimation layer that maps user brush strokes to 3D trajectory data, which the Gen-3 model then interprets during the denoising process. Positioned as a professional-grade VFX tool, it bridges the gap between unpredictable AI generation and traditional keyframe animation, making it a staple in high-end advertising, social media content, and pre-visualization workflows. Its market position is solidified by its deep integration into the Runway Creative Suite, providing an ecosystem where assets move seamlessly from generation to post-production.