How in-browser conversion works, and how to check that nothing is uploaded
2026-10-01
Most online converters work the same way: your file is uploaded to a server, converted there, and offered back as a download. This site does not have a conversion server. The work is done by the browser tab you have open. Here is what that means in practice.
What happens when you drop a file
- The page reads the file into memory. It is a local read, the same as opening a file in any app. No network request is made.
- An engine converts it. Images going to PNG, JPG or WEBP are decoded and re-encoded with the browser's built-in image codecs, which takes well under a second. Everything else is handled by ffmpeg, the open-source media tool, compiled to WebAssembly so it can run inside a web page.
- The result is handed back as a download. The browser creates the output file in memory and saves it to your downloads folder.
The ffmpeg engine is a 32 MB download. It is fetched the first time you convert a video or audio file and cached by the browser afterwards.
Check it yourself
You do not have to take this on trust.
- Offline test. Load a converter page, convert one small file so the engine is cached, then switch off Wi-Fi and convert another. It still works.
- Network tab. Open your browser's developer tools (F12), choose the Network tab, and convert a file. You will see the engine being downloaded, but no request that sends your file anywhere.
The trade-offs
Running in a tab has real limits, and it is better to know them before you start a long job.
| Limit | Why | What to do |
|---|---|---|
| Files over 2 GB are refused | The whole file has to fit in the tab's memory | Use a desktop app for very large videos |
| Video is slow, roughly 0.5–2× real time | The engine runs on a single thread | Use a laptop or desktop; keep the tab open and in front |
| Phones struggle with long videos | Less memory and slower processors | Convert audio and images on the phone, video on a computer |
| DRM-protected files fail | They are encrypted | Nothing can be done; this is by design |
Audio is much lighter than video. A five-minute song converts in a few seconds on most devices.
When a server-based converter is the better choice
If you need to convert a multi-gigabyte recording, a document format, or a file on a device with very little memory, a desktop program or a server-based service will do the job faster. For everything else, and especially for anything private such as screen recordings, voice memos or ID photos, keeping the file on your own device is the safer default.
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