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Video & Audio Tools

Video Subtitle Merger

Combine a video and a subtitle file into one. Add the subtitles as a track – viewers switch them on and off, and the picture is not re-encoded – in MP4 or MKV, with the right language tag and default flag. Or burn them into the picture so they show everywhere, including on platforms and players that ignore subtitle tracks.

  • Files stay on your device
  • No sign-up
  • Free to use

How to use Video Subtitle Merger

  1. Drop the video onto the page.
  2. Choose the subtitle file (SRT, VTT or ASS).
  3. Choose “Add as a track” or “Burn into the picture”.
  4. Process and download.

Video Subtitle Merger features

Soft subtitles

Switchable track, no re-encoding.

MP4 or MKV

mov_text or original format.

Language tags

Players label the track correctly.

Burn-in

Always visible, any player.

Text size

Small, medium or large.

Private

Processed on your device; the video is never uploaded.

When to use Video Subtitle Merger

  • Adding translations to a video for sharing.
  • Posting subtitled videos on social media.
  • Delivering accessible videos.
  • Creating language-learning videos.

Video Subtitle Merger FAQ

Track or burn-in – which should I choose?

A track keeps the original picture and lets viewers choose; burn-in guarantees the subtitles are seen, which is what social media autoplay needs.

Why is adding a track so fast?

The video and audio are copied as they are; only the subtitle stream is added.

Which scripts can be burned in?

The built-in DejaVu Sans font covers Latin, Greek and Cyrillic. For other scripts, add the subtitles as a track, which players render with their own fonts.

Does MP4 keep subtitle styling?

MP4 tracks support plain text. For styled ASS subtitles as a track, choose MKV.

Why does the first run take longer?

The media engine, FFmpeg compiled to WebAssembly (about 32 MB), is downloaded once and then cached by your browser.

Is my video uploaded?

No. FFmpeg runs as WebAssembly in your browser, so the video stays on your device.

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Two ways to add subtitles

Subtitles can be delivered in two fundamentally different ways. Soft subtitles are a separate text stream inside the video file. Viewers can switch them on or off and choose a language, and the subtitles stay sharp at any screen size. Hard or burned-in subtitles are drawn into the picture itself; they are always visible and work in every player, at the cost of flexibility.

For soft subtitles, the merger copies the video and audio unchanged and adds the subtitle file as a new stream. In MP4, text subtitles are stored in the mov_text format that iPhones, QuickTime and most players understand; in MKV, SRT and ASS are stored as they are. The language tag and default flag tell players how to label and whether to show the track.

For burned-in subtitles, FFmpeg renders each cue with libass onto the frames and re-encodes the video. A bundled font is used so the result is the same on every computer, with an outline for readability on any background.

Social platforms usually ignore subtitle tracks in uploaded files and offer their own caption systems; burned-in subtitles are the reliable choice there.

Processing happens in your browser.

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