feat: Add COOP/COEP Headers for Cross-Origin Isolation & FFmpeg Multi-Threading

[Abhi190702]

Summary

Resolves #601

Adds COOP/COEP headers to enable cross-origin isolation and FFmpeg.wasm multi-threaded mode when the deployed host supports it.

Problem

self.crossOriginIsolated currently returns false on the deployed site, forcing FFmpeg.wasm into single-threaded mode. A 1-minute 1080p export can take 3–5 minutes instead of ~30–60 seconds.

Changes Made

vercel.json

• Added Cross-Origin-Opener-Policy: same-origin
• Added Cross-Origin-Embedder-Policy: require-corp
• Preserved all existing routes and security headers

public/_headers

• Added the same headers for Netlify / Cloudflare Pages support

src/lib/ffmpeg.ts

• Added self.crossOriginIsolated runtime check
• Loads @ffmpeg/core-mt when isolated
• Falls back to @ffmpeg/core when not isolated
• Keeps graceful degradation for hosts that cannot enable isolation

CONTRIBUTING.md

• Documented the GitHub Pages limitation for custom headers

Why NOT next.config.ts

This project uses output: 'export' (static export). The headers() function in next.config.ts is silently ignored in static mode. Headers are correctly placed in vercel.json as confirmed by the maintainer.

Performance Impact

Mode	Export time (1-min 1080p)
Before (single-threaded)	~3–5 minutes
After (multi-threaded)	~30–60 seconds

Testing

After deployment, run in DevTools console:
self.crossOriginIsolated -> should return true

Local checks:

• bun run lint
• bunx tsc --noEmit
• bun run build

[vercel]

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[github-actions]

👋 Thanks for your PR, @Abhi190702!

Welcome to Reframe — a browser-based video editor built for everyone 🎬

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Quick checklist

• PR title follows Conventional Commits (e.g. feat: add dark mode)
• Linked the issue this PR closes (e.g. Closes #123)
• Tested the changes locally (bun run dev)
• Build passes (bun run build)

Useful links

• 📖 CONTRIBUTING.md
• 🐛 Open Issues
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Happy coding! 🎉

[github-actions]

✅ PR Format Check Passed — @Abhi190702

Basic format checks passed. A maintainer will review your code changes.

This does not mean the PR is approved — it just means the format is correct.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
reframe	Ready	Preview, Comment	May 23, 2026 10:15am

[Abhi190702]

@magic-peach , Hey I would be grateful if you could look into this
:)
Edit - Please can you add GSSOC tag , so that contribution might count in it thanks