Can I convert files without uploading them?
Yes. Modern browsers can run conversion engines locally using WebAssembly, so your photos, PDFs, audio and video are processed on your own device and never sent to a server. ARTH Convert works this way for every format it supports, including HEIC, PDF, MP3 and MP4.
WebAssembly lets a browser run compiled code at near native speed. Tools such as FFmpeg, the open source audio and video library, can be compiled to WebAssembly and executed inside a web page.
The trade off is speed and memory. Your device does the work, so a very large video can take a while on a phone, but you gain privacy and there is no upload wait.
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Does it need an internet connection?
You need a connection to load the page and, for audio and video, the conversion engine. After that, the processing itself does not send your file anywhere.
Why is video conversion slower than photo conversion?
Video must be decoded and re-encoded frame by frame inside the browser, which takes far more processing than a single image.
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Last updated 9 October 2026. Published by ARTH, the studio behind ARTH Convert.