Scroll-based storytelling, or scrollytelling if you must, treats the vertical position of the page as time. Move down and the story advances. Stop and it holds. Move back and it rewinds. It is the only form of interactive narrative most people already know how to operate, because everyone knows how to scroll.
The pinned stage
The core mechanism is a stage that stays fixed on screen while the page keeps moving underneath it. On the stage, a scene plays out: a product turns, a diagram builds, a landscape assembles point by point. Beside or over it, copy arrives on beats. The scroll distance of the pinned section is the duration of the scene.
Progress, not events
Good implementations map scroll to a continuous progress value between zero and one and drive everything from it: opacity, position, the frame of a film, the number of points drawn. Nothing is triggered; everything is interpolated. That is what makes the page feel like a held object rather than a slideshow, and it is why it works in reverse.
Easing the reader
Raw scroll is jittery. The scene should follow it with a little inertia, catching up over a few frames, so a flick of the wheel becomes a smooth movement. The same goes for the copy: fade and rise over a few hundred milliseconds, not instantly. The reader should feel that they are steering, not clicking.
The scroll bar is the play head. Your job is to decide what happens at every position of it.
Where it fails
It fails when the scene demands more scroll than it earns. Three screens of movement for one idea is a chore. It fails when text and image compete for the same moment, and when the mechanism is louder than the message. And it fails on phones if it was only ever tested on a desktop.
Why it suits campaigns
A campaign has a story with a product at the end. Scroll storytelling gives that story a shape the reader controls, and puts the product where it belongs: at the close, when the case has been made and the buy button is the natural next thing to touch. Built well, the film is the page and the page is the shop.