Why Another Screen Recorder?

Every screen recorder I tried — Loom, CloudApp, Screencastify — uploads your video to their servers. For quick dev demos, bug reports, or client walkthroughs, I just wanted a recording that stays on my machine. No accounts, no uploads, no wondering who else can see my screen.

So I built Jot — a Chrome extension that records your browser tab and processes everything locally. Your video never leaves your device.

How It Works

When you click record, Jot captures your active browser tab using Chrome’s tabCapture API. There’s no clunky share picker — it starts immediately on the tab you’re looking at.

The recording pipeline runs entirely inside your browser:

1. Capture — Chrome’s tabCapture grabs the tab’s video and audio stream
2. Encoding — WebCodecs API encodes frames in real-time using hardware acceleration when available
3. Storage — Chunks are persisted to the browser’s Origin Private File System (OPFS), so even if Chrome crashes mid-recording, your data is recoverable
4. Processing — FFmpeg compiled to WebAssembly muxes the chunks into a standard H.264 MP4
5. Download — You get a .mp4 file that plays everywhere

No server involved at any step.

The Technical Decisions

Why tabCapture Instead of getDisplayMedia?

getDisplayMedia shows that clunky Chrome share picker every time. tabCapture directly captures the active tab — one click and you’re recording. The tradeoff is you can only record browser tabs, not desktop or other windows. For my use case (recording web apps, demos, tutorials), that’s perfect.

Why OPFS for Chunk Storage?

Recording generates a lot of data. Writing it to regular browser storage (IndexedDB, localStorage) would be slow and limited. OPFS gives you a proper file system with synchronous write access from a Web Worker. This means:

• No data loss on crash — chunks are written to disk as they arrive
• Recovery is possible — if processing fails, you can retry from the raw chunks
• No storage quota surprises — OPFS can handle gigabytes

Why FFmpeg in WebAssembly?

The browser records in WebM format, but WebM playback is inconsistent across devices — especially on iOS and older players. FFmpeg remuxes (and when needed, re-encodes) to H.264 MP4, which plays literally everywhere. Compiling FFmpeg to Wasm means this happens entirely in your browser with zero server round-trips.

Adaptive Quality

Jot detects your screen resolution, available memory, and CPU cores to automatically pick the right recording quality — from 1080p30 up to 4K30. You can also manually choose a preset. If your hardware can’t sustain the requested quality, it gracefully falls back.

What I Learned Building This

Chrome extension architecture is surprisingly powerful. Between offscreen documents, Web Workers, OPFS, WebCodecs, and Wasm — you can build genuinely complex applications that run entirely client-side.

The hardest part was state management. A screen recorder has a lot of states: idle, preflight checks, armed, recording, stopping, processing, validating, done, error, recovery. Getting the transitions right — and handling every edge case (tab closes mid-recording, storage runs out, mic disconnects) — took more effort than the actual capture code.

Local-first is a real differentiator. People care about privacy more than I expected. “Your video never leaves your device” is a one-liner that immediately resonates.

Try It

Jot is free and open source. Install it from the Chrome Web Store and record your first video in under 10 seconds.

No account needed. No uploads. Just a recording that stays yours.