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Add Subtitles to Video

Burn SRT, VTT or ASS subtitles into a video with your style, or add them as a switchable track in MP4 or MKV.

Free, no uploads, no sign-up. Runs 100% in your browser.

How Add Subtitles to Video works

Subtitles are drawn with libass inside ffmpeg.wasm using the bundled Liberation Sans font (SIL Open Font License). Separate tracks are added without re-encoding. Video work runs in ffmpeg.wasm, the FFmpeg toolkit compiled to WebAssembly (GPL build, loaded as a separate engine file of about 30 MB the first time, then cached).

Input: MP4, MOV, WEBM, MKV, AVI, SRT, VTT, ASS. Output: MP4, MKV.

How to use Add Subtitles to Video

1. Drop a video onto Add Subtitles to Video.
2. The first run downloads the ffmpeg engine (about 30 MB, once).
3. Set your range, format or quality options.
4. Process it (progress is shown live), then download.

Tips

• Shorter clips and lower resolutions process much faster.
• Processing speed depends on your CPU; plug in laptops for long jobs.
• Keep the tab in the foreground while encoding.

Add Subtitles to Video FAQ

Are my files uploaded?

No. This tool runs entirely in your browser tab. Files are read from your disk into memory and the result is generated locally.

Is it free? Are there limits or watermarks?

Free and open source (MIT). There are no file-size caps, daily quotas, accounts or watermarks.

Does it work offline?

Yes, once the page (and any engine it needs) has loaded, it keeps working without a connection thanks to the service worker cache.

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• Video Trimmer: Trim and cut clips with a visual timeline, no re-upload.