Nothing is uploaded. The conversion runs here, on this device.
AIFF is the uncompressed format Apple audio tools write. Like WAV, it is large.
The conversion happens inside this page. Your file is read by the browser, converted here, and saved straight back to your downloads — it is never sent to a server, so there is no upload wait and no size cap beyond what your own device can hold.
Open your browser's developer tools, switch to the network panel, and convert a file. You will see the converter itself download once, and no upload of your audio at all. That is the whole difference between this and a site that converts on a server.
The converter is about 32 MB and downloads the first time you use it, which is the one moment this page is not instant. After that it is cached, and later conversions — and later visits — start immediately, even offline.
anyaudioconvert · conversion runs on your device