iOS app · Founder · On the App Store
Tandem
An iOS app for making vlogs together: everyone records clips in the same time window, and Tandem cuts them into one video.
- ~3 s
- to render a finished video on the phone
- 9
- video styles, one layout engine
- ~1,400
- automated tests before anything merges
What it is
Tandem is an iOS app for making a vlog with friends. The group picks a stretch of time, everyone records clips during it, and the app cuts them into one stylized 9:16 video. It’s on the App Store, with subscriptions on iOS and Android through RevenueCat.
How it works
- Clips from a shared window
- Tile layout, worked out once
- Preview and export match
- A 9:16 video in ~3 s
One layout for the preview and the export
The renderer is data-driven and has nine styles. It works out the tile layout once, in TypeScript, and both the live preview and the Swift/AVFoundation export draw from that, so they line up exactly. An export renders on the phone in about three seconds. Older videos go through a frozen copy of the layout code, which means re-rendering one gives the same file, byte for byte.
A backend that keeps vlogs apart
The backend is Supabase. Row-level security only lets members into their own vlogs, and tests try to read one vlog from inside another to prove they can’t. Shared boards update live over Realtime. Clips recorded offline wait in an outbox until there’s a connection, and the server keeps a grace window open for late ones.
How a change gets made
Each change gets its own Git worktree. A builder agent writes it, a second model reviews it and tries to break it, and a verifier reproduces every finding. Then about 1,400 automated tests and my own review decide whether it merges.