AAC is the audio standard for lossy digital audio compression. It also happens to be the license-free standard for YouTube, Sony’s PlayStation 3, and is preferred by Apple. If you have an Android phone, you won’t really benefit from AAC as its performance is unreliable: it’s a power-hungry codec that Android remains unprepared to handle efficiently. iPhone users do benefit from its higher-resolution playback though. It has a transfer rate cap of 250kbps, creating a file similar to that of a mid-quality MP3.