AAC (Advanced Audio Coding) is a lossy audio format designed as the successor to MP3. It was standardised in 1997 and became the sound format of the iPhone, iTunes, YouTube, most streaming services and the audio track inside almost every MP4 video. At the same bitrate, AAC generally sounds better than MP3, especially below about 160 kbps.
AAC, .aac and .m4a
AAC is the codec: the way the sound is compressed. It’s usually stored in one of two ways:
| File | What it is | Common sources |
|---|---|---|
.m4a |
AAC inside an MP4 container, with tags and artwork | iPhone Voice Memos, iTunes and Apple Music downloads |
.aac |
Raw AAC stream (ADTS), no container | Android recorders, radio and stream recordings |
.mp4, .mov |
AAC as the sound track of a video | Phone videos, downloads, screen recordings |
The sound is the same; only the packaging differs.
AAC compared with MP3
| AAC | MP3 | |
|---|---|---|
| Quality at 128 kbps | Very good | Good |
| Supported by | Nearly all modern devices | Practically everything |
| Introduced | 1997 | 1993 |
| Typical use | Streaming, video, Apple devices | Music libraries, older players |
AAC’s efficiency is why platforms use it: a smaller file for the same perceived quality. MP3’s strength is universal support, including older car stereos and players.
Variants
- AAC-LC (Low Complexity) is the standard form used for music and video.
- HE-AAC adds techniques that keep low-bitrate audio, such as internet radio at 48 kbps, sounding full.
- xHE-AAC is the newest version, used by some streaming apps to adapt to slow connections.
How to play AAC files
Phones, Macs and modern Windows play AAC out of the box, as do VLC and most music apps. Some older car stereos and MP3 players don’t. For those, convert to MP3 with the AAC to MP3 or MP3 converter tools.
When to use AAC
Choose AAC for music on Apple devices, for audio in videos, and wherever you want the best quality for the file size. Choose MP3 when you need the file to play on absolutely anything.