The motion feature is the temporal input that VMAF adds to its otherwise per-frame, spatial features. It measures how much the picture is moving by computing the temporal difference between neighbouring frames — in the open-source VMAF package, the mean co-located pixel difference on the luma (brightness) channel, that is, how much each pixel changes from one frame to the next at the same location. Motion matters perceptually because the eye forgives more distortion when the scene is moving fast: a still frame is scrutinised, a fast pan is not. Feeding motion into the trained model lets it calibrate how harshly to judge the spatial damage that VIF and the detail-loss metric detect, raising or lowering tolerance with the pace of the action. It is one of the three elementary features in the classic VMAF (v0) fusion. Its catches mirror VMAF's: it is full-reference and the co-located-difference measure is coarse, which is part of why the 2026 v1 high-frame-rate variants use a wider five-frame motion window for fast content.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
The motion feature tells VMAF how much the picture moves, which is why the same artifact scores differently in fast and slow scenes. We wrote seven volumes covering the whole video stack, and for the motion feature start with Volume 1: VMAF and its features, temporal masking, rate control and motion-heavy encodes. Written by Nikolay Sapunov, CEO at Fora Soft.
VMAF behaving oddly on sports or fast-motion content?
Share fast-motion encodes and VMAF logs: we break out the motion feature and tell you whether the score or the encode needs fixing. 250+ video products shipped since 2005.
