There's no quick version, you just gotta start tapping the move faster and immediately after you hit the kick/punch button. Not when the air attack connects, right after you hit the button for the punch/kick.
It's easier to do after a jumping punch, so try that and then move to the kick (kicks cause more damage).
on keyboard u hold UP button and buffer double (or more) forward(for liu, bacward for kabal etc.) while blocking or any move, and when u anticipate the moment char is gonna be able to jump (after the blocking or some move) u press Punch button.
After the 1st early air fireball u can easily buffer those moves again (while your char is in air, shooting ppl) for the next AFball.
There is no sense to do early AFB directly without buffering, u r risking to jump higher, than u needed and eat the punish.
Hmmmmm...sorry for the late response. But when i saw it in those videos its not as easy as jumping and pressing back back x. Because thats what i do already. From what i see in the they use some shortcut to do it off the ground as soon as they jump. Not on the way down from the jump
As Mafioso told you, the philosophy of this thing is to hold up while basically spamming the BACK button. and as soon as you see him going up ,dial HP for the ball. When I used to play KB, I used to press LP and after the LP instant air ball....try it, mix it up and see what works for you.
u will get them out quicker and much more consistent. And suddenly kabal and rep turned into my fav chars. No Macro or Turbo needed , and keys can be binded like this in Mame , and in Epsxe u will need to unbdind R2/L2 within Epsxe and use xpadder to bind these like this.
I hope it helps.