@thisisayande/openscrim-core

@thisisayande/openscrim-core

The engine behind OpenScrim — an open-source, Scrimba-style format for interactive code screencasts. Instead of recording pixels, OpenScrim records editor events (keystrokes, cursor moves, content changes, scrolls) as timestamped data, so a "video" of a coding session is ~100× smaller than pixel video, fully seekable, and forkable: viewers can pause at any moment and edit the instructor's exact code.

This package is framework-agnostic (no React, no Monaco dependency). For wiring it to a Monaco editor, see @thisisayande/openscrim-monaco.

Install

npm install @thisisayande/openscrim-core

What's inside

• RecordingManager — captures editor events into a RecordingSession buffer
• PlaybackEngine — schedules and replays events with play/pause/seek/speed; emits events to your renderer via handler callbacks
• compressEvents / decompressEvents — event-stream compression (cursor dedup, keystroke batching)
• sessionToTantricaFile / writeTantricaBuffer / readTantricaBuffer — the .tantrica file format: gzipped JSON with magic bytes and a fast-readable metadata header
• types — the full RecordingEvent union and RecordingSession model

Quick example

import { PlaybackEngine } from '@thisisayande/openscrim-core';

const engine = new PlaybackEngine();
engine.addEventHandler(({ type, data }) => {
  if (type === 'eventProcessed') renderIntoYourEditor(data);
});
engine.loadSession(session);

engine.play();
engine.seek(30_000); // jump to 0:30
engine.setSpeed(1.5);

Environment notes

• Recording, playback, and event compression work in browsers and Node.
• Reading .tantrica files works everywhere: parseTantricaBytes(bytes) is async and uses Web APIs only (DecompressionStream), so it runs in browsers and Node 18+.
• The synchronous binary helpers (writeTantricaBuffer / readTantricaBuffer) require Node (they use zlib and Buffer); use them server-side. Plain-JSON serialization works everywhere.

Status

0.x — APIs and the file format may still change between minor versions. Feedback and issues welcome at github.com/ayan-de/openscrim.

License

MIT Ayan De