All about AAC files

AAC stands for Advanced Audio Coding and is a lossy compression format for audio files. It often delivers better sound quality than MP3 at the same bitrate and is particularly efficient at lower bitrates. Today, AAC is the standard on Apple devices, for YouTube videos, on Nintendo and PlayStation game consoles, and with many streaming services.

History and development

AAC was developed by a consortium of leading companies, including the Fraunhofer IIS (developer of MP3!), and was officially adopted as a standard by the Moving Picture Experts Group (MPEG) in April 1997. The first commercial use took place as early as 1997 when AT&T launched a digital music shop featuring AAC files. However, the real breakthrough did not come until 2003, when Apple launched the iTunes Store (now Apple Music) and used AAC as its music format.

Technical development

Since the first version, several extensions have been added to the AAC standard. Today, a distinction is made between:

• AAC-LC (Low Complexity) – the most widely used profile, standard on iTunes and most streaming services
• HE-AAC (High Efficiency) – optimised for low bitrates, uses Spectral Band Replication (SBR); defined in 2003
• HE-AAC v2 – adds Parametric Stereo for even lower bitrates; defined in 2004/2006
• AAC-LD (Low Delay) – for real-time communication such as VoIP; defined in 2000
• xHE-AAC (Extended HE-AAC) – the latest variant, combines speech and music encoding for adaptive streaming

Patents and licensing

Unlike MP3, which has been patent-free since 2017, AAC is still subject to patent protection. Patent holders include Fraunhofer, Dolby, Sony, Philips and Microsoft. The last basic patents for AAC are expected to expire in 2028, whilst patents for extensions such as HE-AAC remain valid until at least 2031.

AAC vs. MP3

AAC was developed to replace MP3. Technically, it has succeeded: AAC uses more efficient compression and an improved psychoacoustic model, meaning it can better distinguish between audible and inaudible sound components. In practice, this means that AAC can deliver smaller files at the same quality or better quality at the same file size. Nevertheless, AAC has not been able to supplant MP3; the head start was too great, the technical differences too small. Consequently, both formats exist side by side today, each with its own advantages.

Sources

• Wikipedia: Advanced Audio Coding
• Fraunhofer IIS: MP3 and AAC explained (PDF)

Last updated on 16. March 2026 by Sören with the experience of more than 128,119,302 converted files since 2013.