Rubbery Motion in Generated Video: Causes and Fixes

There is a characteristic defect in video generation that is hard to name in one word: objects move as though made of something soft. Shoulders stretch, objects change shape mid-motion, edges float. In professional usage this is called rubbery motion.

Where the effect comes from

The model does not know that objects are rigid. It has no notion of skeletons, joints or material stiffness — only statistics about how frame sequences look.

When it builds intermediate states between the start and end of a movement, it interpolates visible form rather than a physical body. If the interpolation passes through a physically impossible state, the model does not notice: locally each frame looks plausible.

Where it breaks worst

• Limbs in wide movements: an arm raised overhead can "lengthen" in intermediate frames.
• Rigid objects in hands: a cup, a book, a phone change proportions.
• Clothing with defined geometry: collars, lapels, button plackets.
• Glasses: the frame deforms as the head turns.
• Architectural elements in the background: straight lines bend.

What reduces it

1. Small movement amplitude. The less an object travels, the shorter the interpolation path and the lower the chance of passing through an impossible state.
2. A slow tempo. Same reasoning: slow motion divides the path into more small steps.
3. A short clip. Fewer frames, less accumulated distortion.
4. No rigid objects in frame. Hair and fabric deform naturally; a cup does not.
5. Simple clothing without pronounced geometry.
6. A soft background without straight lines: a bent wall is obvious, a bent tree canopy is not.

Phrasings that help

Stating the character of the movement works better than stating what should not happen.

• "Slow smooth movement" instead of "no deformation".
• "A slight head tilt" instead of "a turn" — smaller amplitude.
• "Camera static, only the background moves" — takes load off the figure.
• "The pose does not change, only the hair moves" — explicitly limits the zone of change.

Choosing a frame for motion

Some compositions are inherently resistant to the defect. A waist-up portrait with hands out of frame, simple clothing, a blurred background — here only the face and hair move, which is exactly what deforms naturally.

Conversely, a full-length frame of someone in a jacket holding an object against a building with straight lines is a collection of everything that produces rubberiness at once.

When the effect is acceptable

In stylised clips that make no claim to realism, mild plasticity of movement does no harm and sometimes suits the material. The problem arises only when the frame claims photographic realism: the mismatch between a realistic picture and impossible physics registers instantly.

Checking

Step through the clip frame by frame in the middle of the motion — that is where interpolation is furthest from its anchors. Check limb proportions, the shape of rigid objects and straight lines in the background. If the middle holds up, the clip passes.