feat: Add Captions/Subtitles Support with Custom Styling Options #991

[Rucha0901]

Description

This PR adds complete support for uploading, previewing, and burning in captions/subtitles from .srt files directly within Reframe.

• SRT Parsing Module: Implements a robust .srt parser (src/lib/subtitles.ts) supporting time range parsing, multi-line blocks, and alternative punctuation.
• Typography & Styling Controls: Added sidebar controls in SubtitleControls.tsx for Font Family, text color, scale size, and background style presets.
• Readability Styles: Support for Plain Text, Black Outline (utilizing professional paintOrder styling to avoid fill bleed), Translucent Background Box, and Drop Shadow.
• Synchronized Playback Preview: Overlays real-time, responsive subtitles on the video canvas scaled proportionally to the current preview container size.
• Word-Search Segment Navigation: A scrollable segment list in the sidebar that allows users to search captions and click a segment to seek the player directly to that time.
• FFmpeg Web Worker Burn-in: Integrates dynamic drawtext filters with enable='between(t, start, end)' inside the background ffmpeg.worker.ts Web Worker during export. This avoids WebAssembly -vf subtitles core crashes and guarantees offline burn-in reliability.

Related Issue

Closes #991

Type of Contribution

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

[vercel]

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[github-actions]

👋 Thanks for your PR, @Rucha0901!

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)
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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
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Happy coding! 🎉

[github-actions]

✅ PR Format Check Passed — @Rucha0901

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[Rucha0901]

@magic-peach ,check the PR.