Don't judge the racking horses by the Undertaker. His gait is the results of being taught to gait the hard way, and is now lame and unusable. He DOES NOT HAVE the genes I'd want in a racking horse.
Your are right about what they are calling a rack in the first video. That's not a rack. It's broken gait. If one of my horses did that they'd go to the glue factory. Here's a racking horse.
Now for any of you good with video captures and timing, the distance between those posts is 10 ft. If you do you math, you'll find