AAC vs. MP3
AAC is the successor to MP3 and offers slightly better sound at the same file size. It’s used by Apple, YouTube, streaming and many recording apps. Still, plain .aac files aren’t supported everywhere – older car radios, MP3 players, some editing tools and upload forms expect MP3, which remains the most widely compatible audio format.
What changes
AAC is decoded and re-encoded as MP3. Since both are lossy, a tiny bit of quality is lost, which is rarely audible. File sizes are similar. Raw .aac files often contain no or little metadata, so you may need to add title and artist afterwards.
How to convert
Drop the AAC file above, MP3 is preselected, click “Convert” and download. FFmpeg runs on your own device in the browser, with no upload.