Difference between speedAtTime() and velocityAtTime()

speed is always a positive number (for a point property: in px/sec, for an angle: in degrees/sec, etc,)

velocity is a quantity that encapsulates both the speed and the direction of change, and has the same dimension as the value :

for a slider, angle,etc, any 1D property : it is the speed times +1 or -1 (+1for positive change rate, -1 for negative)

for a property whose value is an array (point, color), it is an array/vector of the same dimension, whose length is the speed, and also give the direction of change (for a point: direction of movement)

Probably the first paragraph of Velocity - Wikipedia, the free encyclopedia is more clear than me.

Xavier