zerotoneroAcademy · Lesson 1 of 9 · 7 min
A-roll and B-roll: why your app promo needs both
A-roll tells the story, B-roll proves it. Learn the two tracks every app promo runs on and why one without the other falls flat.
Every promo video you have ever scrolled past runs on two tracks, even if nobody called them that. A-roll is the main narrative: the thing that carries the story from start to finish. For an app promo that is usually you talking to camera, a voiceover, or a screen-recording walkthrough where the app itself is the narrator. If you muted everything else and kept only the A-roll, you should still be able to follow what the video is about.
B-roll is everything you cut over or between the A-roll to show, prove, or add energy. Close-ups of your UI, a zoom into a screen recording, your phone in someone's hand on a bus, a reaction shot, a quick motion graphic, a text overlay, the occasional stock clip. B-roll rarely makes sense on its own. Its job is to make the A-roll believable and watchable.
Think of it like your codebase: A-roll is the main function, B-roll is the set of helpers that make it readable. A main function that does everything inline technically works, but nobody wants to review it. A pile of helpers with no main is just a library nobody calls.
App promos fail in two predictable ways. The first is all A-roll: you, talking to a camera for 30 seconds, describing a feature the viewer never sees. The second is all B-roll: a slick montage of UI shots set to music, with no story tying them together, so the viewer sees a lot and understands nothing. The fix for both is the same: decide what the story is (A-roll), then decide what each moment needs to show (B-roll).
A practical way to start: write your script as five beats (hook, problem, solution, proof, CTA). Pick one A-roll mode per beat: talking head, voiceover, or screen walkthrough. Then, under each line, write the shot that would make a skeptical viewer go 'oh, I see it'. That second track is your B-roll plan. If a line has no shot under it, ask whether the viewer needs to see something there. Usually they do.
Balance does not mean 50/50. A talking-head hook might need no B-roll at all for the first second, while a proof beat might be almost pure B-roll with your voice underneath. What matters is that the viewer is never asked to imagine something you could have shown them.
Key points
- A-roll carries the story: you on camera, a voiceover, or the main screen walkthrough.
- B-roll shows and proves: UI close-ups, phone-in-hand, reactions, overlays, motion graphics.
- All A-roll feels like a lecture; all B-roll feels like a montage with no point.
- Plan the story first, then write the shot that proves each line underneath it.
Good: Story on top, proof underneath
A made-up habit tracker that keeps your streak alive on rest days. You carry the story; B-roll shows every claim as you make it.
- 1s You set up the story; a close-up proves it within the first seconds.
- 7s Voiceover explains while the screen shows. Nobody has to imagine the UI.
- 13s Proof is footage, not adjectives.
- 18s The CTA is said and shown, so it lands with or without sound.
Bad: The 20-second lecture
Same app, same script, but it is all A-roll. Every feature is described and none is shown.
- 2s The hook is a promise with nothing to look at.
- 4s Your delivery is fine. The problem is the edit, not you.
- 9s 'A rest-day button' explained in words only. Viewers have to picture your UI.
- 14s 'It really works' is a claim. Where is the footage?
- 18s First and only B-roll arrives at 18 seconds, long after a scroller has moved on.
Common mistakes
- Talking for the whole video and never showing the app.
- Cutting a music montage of UI shots with no story connecting them.
- Planning B-roll after filming, so the shots you need were never captured.
- Using B-roll as decoration (pretty desk, coffee cup) instead of showing what you are saying.
- Treating balance as a fixed ratio instead of asking what each beat needs.