feat: restore Node.js support via worker_threads

[JacobiusMakes]

Summary

Resolves #897 — restores Node.js support that was removed in v0.12.0.

With both fluent-ffmpeg (archived May 2025) and ffmpeg-kit (archived June 2025) now dead, there is no maintained way to use FFmpeg from Node.js without native binaries. This PR brings ffmpeg.wasm back to Node.js with a zero-change API — existing browser code works in Node.js by swapping the import.

What's included

• node-classes.ts — FFmpeg class using worker_threads.Worker instead of Web Workers. Same public API as the browser version.
• node-worker.ts — Worker script using parentPort message passing. Mirrors the browser worker.ts exactly.
• @ffmpeg/util/node — Node.js fetchFile() supporting local file paths (fs.readFile), URLs (fetch), Buffers, and base64 data URIs.
• Updated empty.mts — Now re-exports the real Node.js implementation instead of throwing.
• Integration test — tests/node-ffmpeg.test.mjs

Design decisions

• worker_threads over direct execution — Keeps transcoding off the main thread, preserving Node.js async behavior. The message-passing protocol is identical to Web Workers.
• No new dependencies — Uses only Node.js built-ins (worker_threads, fs, url).
• Backward compatible — The package.json exports field routes Node.js to the new implementation via the existing "node" condition. Browser builds are unchanged.

Usage

import { FFmpeg } from "@ffmpeg/ffmpeg";
import { fetchFile } from "@ffmpeg/util/node";

const ffmpeg = new FFmpeg();
await ffmpeg.load();
await ffmpeg.writeFile("input.mp4", await fetchFile("/path/to/video.mp4"));
await ffmpeg.exec(["-i", "input.mp4", "output.mp3"]);
const data = await ffmpeg.readFile("output.mp3");

Test plan

• Verify node-classes.ts correctly spawns node-worker.ts via worker_threads
• Test fetchFile with local paths, URLs, base64, and Buffers
• Confirm browser builds are unaffected (exports field routing)
• Run tests/node-ffmpeg.test.mjs with @ffmpeg/core installed
• Verify terminate() cleanly shuts down the worker thread

🤖 Generated with Claude Code

[netlify]

✅ Deploy Preview for ffmpegwasm canceled.

Name	Link
🔨 Latest commit	5ae1a4e
🔍 Latest deploy log	https://app.netlify.com/projects/ffmpegwasm/deploys/69c5d0b34076a40008c4ec5f