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ConvertBox

Add subtitles to video

Burn SRT/VTT subtitles into your video or embed them as a soft track. Runs entirely in your browser — files never leave your device.

Video file

🎬

Select a video

MP4, MOV, WebM — up to 50MB

Max file size: 50MB

or drag and drop · press Enter to browse

Subtitle file

💬

Select an .srt or .vtt

SRT or VTT format

Max file size: 5MB

or drag and drop · press Enter to browse

How to Use

  1. Pick the video file (max 50MB).
  2. Pick an SRT or VTT subtitle file.
  3. Choose between burn-in or soft subtitle mode.
  4. Click Add subtitles — your subbed MP4 will be downloaded.
  5. Verify the output file in your device's download folder.
  6. You can adjust settings and process new files immediately without any restrictions.

All processing is done in your browser, and files are never sent to a server.

Frequently Asked Questions

Burn-in renders the subtitles into the video frames so they're always visible. Soft subtitles are a separate track that the viewer can turn on/off.
No. Encoding runs in your browser via FFmpeg WebAssembly. Your files never leave your device.
MP4 with H.264 is the most universally compatible format. The original codec is re-encoded for accuracy when burning subtitles in.
No. All operations are processed entirely inside your browser's local sandbox using client-side APIs (like WebAssembly, pdf-lib, or HTML5 Canvas). Your files and data never leave your device.
The tool is completely free with no usage limits. However, since processing occurs in your browser's memory, we recommend keeping file sizes under 50MB (especially for heavy files like PDFs or videos) to ensure stability.
No. All tools on ConvertBox are 100% free. We do not insert watermarks, limit features, or require any registration or payment.
Yes. Once the page and its local library dependencies are loaded in your browser, the conversion logic runs completely offline without needing an active internet connection.

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