Motion Key

Pulls an alpha matte from frame-to-frame motion: whatever is moving keys in.

Parameter	Control	Range	Notes
Sensitivity	Trough	0 to 1
Softness	Trough	0 to 0.5	Feathers the matte’s edge.

Outputs an alpha-only matte, not a recolored image, and takes the same two parameters as Luma Key.