In Encode mode choose an audio file and copy the generated data URI. In Decode mode paste a data URI or raw Base64, then play the result and download it as a file.
It embeds a sound directly in HTML, CSS or JavaScript so the page needs no extra network request. That suits tiny interface sounds, email-safe assets, and offline single-file demos.
Base64 represents three bytes with four characters, so encoded data is about 33 percent bigger than the original file. That is why data URIs suit short clips and are a poor choice for full songs.
No. The file is read with FileReader and converted to Base64 in your browser's memory. The resulting string only ever exists on your device unless you paste it somewhere yourself.