Agree on the slider.
The sinking fastball in the second clip bears in on RHH because of the spin.
If you imagine looking straight down at the pitcher from an overhead position, at ball release he puts backspin on the ball that would look "clockwise" from overhead.
The physics of spinning balls is complex but, if the spin axis of the ball is perpendicular to the direction of flight, as it is for all fastballs, the Magnus force on the ball is at its greatest. The Magnus force of a spinning ball tends to make the ball veer off of its original path, in the direction of the spin.
Since that ball is spinning clockwise, from the overhead vantage point, you would expect to see it veer off a straight path...to the right-hand side.
For another good example, check out Jeff Nelson's slider/2-seamer combo...
I think the reason why you don't necessarily catch any pronation in the clips you showed is: They were filmed at slow frame rates, and then slowed down even more for playback. To reliably catch fast motions like pronation after release it is better to film at very high speeds and slow down the playback.