Private video utilityNo uploads

Burn subtitles in.
Keep everything else.

Add captions to your video without sending it anywhere. Subwasm runs FFmpeg in a browser worker and writes the finished file back to your device.

Private by defaultMedia stays in this browser

Built for big filesOPFS stages from local disk

Start a local job

Ready when you are.

JOBLOCAL / 001

01 / Add your files

One video and one .srt. Both are stored locally as they arrive.

Checking storage

Drop a video here MP4, MKV, MOV, WebM, AVI · any size Choose file ↗ Drop your subtitle file SubRip subtitle .srt only Choose file ↗

Your files never leave this tab. OPFS keeps the source off the main memory path.

02 / Preview & process

Your finished video will be saved directly to your disk.

MP4 output

Preview appears here Choose a video to load a local preview

Input videoWaiting for a video

Outputsubtitled-video.mp4

The engine runs in a background worker.

Checking the capabilities this browser can use.

OPFS stagingchecking

FFmpeg workerready

JSPIchecking

Pick a video and an .srt file to get started.

Why this feels different

There is no account, cloud queue, or media endpoint. Your files stay on your machine.

OPFS keeps the source file on local storage so the page does not need to swallow the whole thing at once.

Subtitles are burned into the picture, so the result plays with captions wherever you take it.