What is AAC (Advanced Audio Coding)?
Definition
AAC (Advanced Audio Coding) is a lossy audio codec that shrinks sound by permanently discarding data the ear is least likely to notice. It is the default audio format for MP4 video, Apple devices and most streaming, and at the same bitrate it usually sounds better than MP3.
AAC works by analyzing audio and removing detail that human hearing struggles to perceive, then packing the rest into a much smaller file. This is lossy compression: the discarded data is gone for good, so an AAC file can never be restored to a bit-perfect copy of the original recording. The payoff is a small file with sound quality close to the source.
AAC is nearly everywhere. It carries the audio in most .mp4 videos alongside H.264 or H.265 video, and it is the standard for Apple Music, iTunes, YouTube and many streaming services. Common bitrates run from 128 kbps for everyday listening to 256 kbps for higher quality; a higher bitrate keeps more detail but makes the file larger.
A frequent mix-up is confusing the codec with the file extension. AAC is the codec (the way the audio is encoded), while .m4a and .aac are file extensions that usually hold AAC audio. People also confuse AAC with MP3: both are lossy, but AAC is newer and typically delivers better quality at the same bitrate.
Quick facts
- AAC stands for Advanced Audio Coding
- Lossy codec: discarded audio data cannot be recovered
- Default audio codec for MP4 video and Apple devices
- Common AAC bitrates are 128 to 256 kbps
- AAC usually sounds better than MP3 at the same bitrate