[BUG] `not-found.tsx` is incompatible with static export — breaks `next build`

[AbhishekChamp879]

Bug description
src/app/not-found.tsx exists in the codebase, but the project uses output: "export" in next.config.ts (static export mode). Next.js does not support not-found.tsx with static exports — it will cause the production build (next build) to fail.
This is explicitly documented as a critical rule in CLAUDE.md:
Static export: output: "export" is set in next.config.ts. This means: not-found.tsx is incompatible — reject PRs adding it . The file was likely introduced in a PR that bypassed this check.

Steps to reproduce

1 . Clone the repository
2 . Run bun install
3 . Run bun run build
4 . Build fails with a Next.js static export error related to not-found.tsx

Expected behavior
bun run build should complete successfully and output a static site to out/.

Actual behavior
The build fails because not-found.tsx is not supported in static export mode (output: "export"). Next.js static export does not generate a server runtime, so dynamic error pages like not-found.tsx cannot be rendered.

Browser and OS info

• OS: All (build-time issue, not browser-specific)
• Browser: N/A
• Version: N/A

Video format (if relevant)

• N/A — this is a build configuration issue, not a video processing issue.

Screenshots/screen recording

• N/A — reproducible by running bun run build.

[github-actions]

👋 Thanks for opening an issue, @AbhishekChamp879!

Our maintainers will review this shortly 🚀

Before you start working

• 📖 Read the CONTRIBUTING.md guide
• 💬 Wait for a maintainer to assign you the issue before starting work
• 🔍 Search for existing issues to avoid duplicates

For GSSoC'26 contributors

If you're contributing under GirlScript Summer of Code 2026, please mention it in your comment when requesting assignment:

"I'd like to work on this — contributing under GSSoC'26"

Architecture notes

Reframe is a static Next.js app with output: "export". Key points:

• All video processing uses FFmpeg.wasm (client-side, no server)
• headers() in next.config.ts won't work — use vercel.json instead
• not-found.tsx requires public/404.html + vercel.json routes config

Happy contributing! ⭐ Star the repo if you find it useful!

[AbhishekChamp879]

/assign gssoc

[github-actions]

Hey @AbhishekChamp879, this issue has been assigned to you! 🎉 Please make progress within 5 days or it will be automatically unassigned due to inactivity.