I get some of that "crackely" chert sometimes, it's usually translucent amber with no cortex and it is absolutely unknappable. The piece I busted up in the first video was very low quality overall with two or three usable sections of decent material. I got four blanks out of the whole rock and ruined two of them on the stake, so pretty low yield.
Softball sized is good. If they're round nodules without a platform to start from, place them on an anvil stone and crack them in half with a sledgehammer. This should give you a nice platform all the way around the edge of the hemisphere from which to work blades.
I didn't describe the striking angles nor the edge preparation as it's all variable and part of the learning curve. Also, if the face of the billet is rough from using it to chip and grind platform edges like I was doing in the video as an expedient to a grinding stone, it can skip and drive off a stack of very thin flakes like the pair I got a time or two. If spalling high quality rock, it will be much worse. File the face smooth for smooth rock to prevent that.