Runway Motion Brush guide
Runway’s Motion Brush gives you region-level control over video generation: you paint the parts of a still image that should move and assign each one a direction and strength, while unpainted areas stay calm. This guide turns an animation goal into a concrete stroke plan — how many strokes, where to place them, and how much intensity to dial in.
How it works
The brush works in layers of independent motion. Each stroke defines a region and a vector (which way it drifts) plus an intensity value. Because the model respects your painted boundaries, the discipline is to keep distinct motions on distinct, non-overlapping regions: one stroke for rippling water, another for drifting clouds, another for a subject’s hair. Foreground subjects usually need lower intensity to avoid morphing, while background ambient elements can take stronger, looser strokes.
Subject-by-subject stroke guidance
Different subjects behave very differently under the Motion Brush. Here is how to approach the most common animation targets:
Water (ocean, rivers, rain): Paint broadly across the water surface with a horizontal or slightly angled vector matching the direction of flow. Intensity 3–5 for waves; 1–2 for a calm lake or puddle reflection. Avoid painting right to the shoreline — leave a small buffer so the boundary with land does not warp.
Clouds and sky: Light, slow strokes across the entire cloud mass. Vector pointing in the prevailing wind direction. Intensity 2–4. Do not paint too close to the horizon line or sharp edge artifacts appear where sky meets ground.
Hair and fabric: Paint the ends of hair or the hem of a dress with a gentle downward or lateral vector; leave the roots or attachment points unpainted so the motion reads as natural swing rather than floating. Intensity 2–3. Hair distorts badly at high intensity.
Foliage (trees, grass): Small oscillating motion is the goal. Paint loosely across the canopy with a slight horizontal vector. Intensity 2–4. Precise brushing of individual branches usually warps more than a broad loose stroke does.
Faces and hands: Leave these unpainted whenever possible. These are the first regions to exhibit morph artifacts. If the scene requires a person to move, start with the lowest intensity available and preview before committing.
Fire and smoke: Motion Brush works well for slow-rising smoke or drifting embers. Use upward vector, loose brushing, intensity 3–5. Fast fire is better guided by prompt than by brush.
Stroke planning tips
One stroke per motion. Independent movements get independent regions. Overlapping strokes fight each other and cause warping where the vectors disagree.
Match prompt to brush. If you brush leftward water flow, the text prompt should not imply a still pond — conflicting cues push the model in two directions and produce neither cleanly. Keep prompt and brush consistent in direction and style.
Build up intensity gradually. Render at the lowest useful intensity first. If the motion reads as too subtle, increase by one step at a time. High intensity on detailed subjects is the most common cause of unnatural morphing.
Use the unpainted area as an anchor. Regions with no brush strokes tend to remain stable. Placing key focal points — a face, a text element, a sharp architectural line — in the unpainted zone keeps them crisp while the brushed areas animate around them.