I finally got the video to work (without sound) by downloading it. The first knot looks like a slippery half-hitch. The second is a power-cinch. It is exactly the knot I use. Very useful. 2:1 mechanical advantage and comes apart with a tug, even wet. Good for tarps, which can be unstable in the wind unless very taught, good for tying down lumber on a car also!
I learned about this knot in the book "Camping's Top Secrets" by Cliff Jacobsen.