feat: add client-side video merge/concatenate support

[chavanGaneshDatta]

Description

This PR adds full client-side video merge / concatenate support to Reframe using the existing FFmpeg.wasm pipeline.

Previously, Reframe only supported workflows involving a single uploaded video. With this implementation, users can now upload multiple clips, rearrange them, preview individual clips, and export them as a single merged video directly in the browser.

Features Implemented:
Added support for multiple video uploads
Added clip sequencing UI
Added clip reordering support (move up/down)
Added clip removal support
Added clickable clip previews
Integrated multi-video merge support into export workflow
Implemented client-side video merging using FFmpeg.wasm
Added clip normalization pipeline for stable playback across different video formats
Added merged video metadata extraction (resolution support)
Preserved existing single-video workflows without regressions
Improved accessibility for interactive clip controls

Related Issue

Closes #427

Type of Contribution

• Bug fix
• New feature
• Documentation update
• GSSoC contribution

Participant Info

• GitHub username: @chavanGaneshDatta
• Contribution level: Advanced

Screen Recording

Reframe.Resize.trim.and.export.videos.in.your.browser.-.Brave.2026-05-21.23-54-17.-.Trim.mp4

Exported Successfully Image

Output Merged Video

Media.Player.2026-05-22.00-02-12.mp4

Checklist

• I have read the contribution guidelines
• My changes follow the project structure
• I have tested my changes in Chrome, Firefox, and Safari
• bun run lint passes (no ESLint errors)
• bunx tsc --noEmit passes (no TypeScript errors)
• New interactive elements have aria-label / accessible names
• No console.log statements left in
• This PR is related to a valid issue
• Screen recording attached above (required for UI/feature/design changes)

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[github-actions]

👋 Thanks for your PR, @chavanGaneshDatta!

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

🟠 GSSoC'26 PR detected — thanks for contributing under GirlScript Summer of Code 2026!

What happens next

1. 🤖 Automated checks — build & TypeScript typecheck will run automatically
2. ✅ Vercel preview — a preview deployment will be created (requires maintainer authorization for fork PRs)
3. 👀 Code review — a maintainer will review your changes
4. 🚀 Merge — once approved, your PR will be merged!

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
• ⭐ Star the repo to support the project!

Happy coding! 🎉

[github-actions]

✅ PR Format Check Passed — @chavanGaneshDatta

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.

[chavanGaneshDatta]

Hi @magic-peach 👋

Just following up on this PR whenever you get a chance.

The merge/concatenate feature implementation is complete, conflicts have been resolved with the latest upstream changes, and the workflow/build checks should now be up to date.

I’d really appreciate a review whenever possible. Thanks!

[magic-peach]

@chavanGaneshDatta The client-side video merge feature using FFmpeg.wasm is a great addition! The approach of extending the existing ffmpeg.ts pipeline is correct.

However, there are some issues before this can be merged:

1. No build/lint/typecheck CI has run — please push an update to trigger full CI.

2. Merge conflicts with main — please rebase on the latest main and resolve conflicts.

Steps:

git fetch upstream
git rebase upstream/main
# Resolve conflicts in VideoEditor.tsx, FileUpload.tsx, useVideoEditor.ts
git push --force-with-lease origin feature/video-merge-support

3. Careful review needed — since this touches src/lib/ffmpeg.ts (the core video processing engine), please make sure:
   • Existing single-video export still works correctly
   • The mergeVideos function doesn't break any existing exports
   • Memory is properly managed (files written to FFmpeg's virtual filesystem are cleaned up)

Once CI passes and conflicts are resolved, this will get a thorough review!

[chavanGaneshDatta]

Hi @magic-peach 👋

I’ve now completed the requested rebase against the latest upstream/main and resolved all merge conflicts in:

• VideoEditor.tsx
• FileUpload.tsx
• useVideoEditor.ts

Additionally:

• verified existing single-video export flow still works
• verified multi-video merge/export workflow
• fixed a post-rebase FFmpeg loading regression
• confirmed cleanup handling for temporary FFmpeg virtual FS files
• confirmed bun run build, bun run lint, and bunx tsc --noEmit all pass locally

Latest fixes and validation updates have been pushed to the PR branch for review. Thanks!

[chavanGaneshDatta]

Hi @magic-peach 👋

The latest rebase conflicts have now been fully resolved, including the remaining package.json, bun.lock, and src/lib/ffmpeg.ts conflicts from the final replayed commits.

I also verified again that:

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

The updated branch has been force-pushed successfully and should now be ready for review. Thanks!

[chavanGaneshDatta]

@magic-peach please check my pr whenever you have time. Thank You

[chavanGaneshDatta]

@magic-peach please check my pr whenever you have time. Thank You

[chavanGaneshDatta]

@magic-peach please check my pr whenever you have time. Thank You

[chavanGaneshDatta]

@magic-peach please check my pr whenever you have time. Thank You. It is pending since nearly a month

[chavanGaneshDatta]

@magic-peach please check my pr whenever you have time. Thank You. It is pending since nearly a month