Pink spherical rollers slide in grooves of yellow shaft. Changes in the drive angle causes the rollers to move backwards and forwards along the grooved track as the joint rotates through one revolution. A small clearance is given between the roller and track to permit this movement.
The video shows the transmission when α (angle between two shafts) is 0 deg. and then 15 deg.
The simulation shows that the output shaft rotates nearly regularly with max error of 3.4% at α = 15 deg.