Now that you put it like that, it makes sense. I guess that's why they say Zangief's ultra 1 is "0 frame start up" but is listed as 1f start up and can punish -1 moves...
Still though, how is it that you can safe jump 4f reversals. This isn't for sake of argument, I really wonder why that is. Maybe SRK got it wrong to say that the game has 4f landing frames? It would make sense if it was 3 landing frames because you can always throw tech from it just like how you can throw tech even when you're -3...
Hi, signed up to answer this.
Landing frames in SF4 work like this (AFAIK). There are 4 frames of landing recovery but it's broken up into 2 categories. The first 2 frames of landing recovery you can't do ANYTHING. The 3rd and 4th frames of landing recovery you can't do anything BUT block.
So against ryu's 3 frame DP what ends up happening is this:
First frame: YOU - last frame of your jumping attack THEM - 1st Frame of their invincible DP
Second frame: YOU - 1st frame of landing recovery, can't do shit THEM - 2nd frame of their invincible DP (still not active)
Third frame YOU - 2nd frame of your landing recovery, still can't block, getting punched in the face THEM - 1st active frame of 3 frame reversal DP punching you in the face.
4 frame normals are safe because by the 4th frame you are still in landing recovery but you can block (just not do anything else).
I should mention, this only applies if you do a NORMAL attack jump in. If you do an empty jump there is less of a landing recovery penalty, you can do anything but move/dash/jump in this case which is why you can 'empty jump' 3 frame DP's all day long.
(EDIT) RE Zangief's 0 frame startup ultra. It's listed as that because their's literally NOTHING you can do to prevent Zangief's ultra from landing unless you did something before the ultra animation to prevent it (jump, invincible/throw immune move). Once that screen freezes for the ultra if you aren't in an unthrowable state (or in range) you're ass is thrown.