How to convert files without uploading them
By Ajiri Ogba · Updated
Use a converter that runs in your browser instead of on a server: the file is read from your disk into the browser tab, converted there, and saved back to your device, so it never travels over the internet. Desktop tools such as ffmpeg do the same offline.
Why it matters
Most online converters upload your file to their servers, convert it there and keep it for a while before deleting it. That's fine for a holiday photo, but not ideal for a bank statement, an ID scan, a contract or private video. When conversion happens on your own device, there is no copy anywhere else to leak, store or delete.
How in-browser conversion works
Modern browsers can run compiled code at near-native speed through WebAssembly. That lets real tools like ffmpeg (for video and audio) and libheif (for HEIC photos) run inside a web page. Simpler jobs use features built into the browser: the Canvas API re-encodes images, and JavaScript libraries such as pdf-lib and pdf.js edit and render PDFs.
Step by step on this site
- Open the converter for your format, for example MOV to MP4 or HEIC to JPG.
- Drag your file onto the page or click to choose it. It's read into the tab's memory, not sent anywhere.
- Press Convert. Video and audio tools download the ffmpeg engine once (about 30MB) the first time.
- Download the result. Closing the tab without downloading discards it completely.
Limits of converting in the browser
- Speed: video encoding uses one CPU core here, so it's slower than desktop software
- Memory: the whole file is held in memory, so very large files need a capable device (this site accepts up to 500MB, or 200MB for PDFs)
- Formats: browser tools support fewer formats than large server-based services
Offline alternatives
- ffmpeg on your computer: every video and audio tool page on this site shows the exact ffmpeg command it runs
- Built-in apps: macOS Preview and Windows Photos can export some image formats