MP3's designated successor and the audio in most video - YouTube, streaming services, broadcast, virtually every MP4. At a given bitrate it beats MP3 audibly, especially below 128kbps, and every phone and browser decodes it.

Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop an AAC file above and choose afterwards.