AAC

Advanced Audio Coding, commonly known as AAC, is a lossy audio compression codec that has become the dominant standard for a wide range of digital audio applications. Its ability to deliver high-quality audio at relatively low bitrates has made it the go-to codec for streaming, digital broadcasting, and portable media players. DivX Software supports the playback of AAC audio to deliver a true cinematic experience.

Understanding the Basics

AAC is a successor to the older MP3 format and was designed to offer better audio quality at similar or lower bitrates. It’s standardized as part of the MPEG-4 specification (ISO/IEC 14496-3) and also within other standards like MPEG-2 Part 7. Various profiles of AAC exist, each optimized for different applications and offering varying levels of complexity and efficiency. Common profiles include LC-AAC (Low Complexity), HE-AAC (High-Efficiency AAC), and HE-AACv2 (Enhanced High-Efficiency AAC).

Key Features and Advantages

AAC’s widespread adoption is due to its numerous advantages:

• Improved Audio Quality: Compared to MP3 at the same bitrate, AAC generally offers superior audio quality with greater clarity and detail, especially at lower bitrates.
• Higher Efficiency: AAC achieves better compression efficiency than MP3, allowing for smaller file sizes without a significant loss in perceived audio quality.
• Multi-Channel Audio Support: Unlike MP3, AAC natively supports multi-channel audio, making it suitable for surround sound applications in movies and home theater systems.
• Variable Bitrate (VBR) Encoding: AAC supports VBR encoding, which allows the bitrate to dynamically adjust based on the complexity of the audio signal. This results in more efficient use of bandwidth and better overall quality.
• Scalability: AAC’s different profiles offer scalability, allowing for optimization based on the specific application and available resources. HE-AAC and HE-AACv2, for example, are designed for very low bitrate streaming while maintaining acceptable quality.
• Wide Device and Software Support: AAC is supported by a vast array of devices and software, including smartphones, tablets, computers, portable media players, streaming services, and digital broadcasting systems.
• Mandatory for Many Platforms: AAC is a mandatory or highly recommended audio codec for many platforms and services, including Apple’s ecosystem (iOS, macOS, iTunes), digital radio standards like DAB+, and various streaming services.

Practical Applications

AAC’s efficiency and quality have made it the preferred codec for a wide range of applications:

• Music Streaming Services: Platforms like Spotify, Apple Music, and Deezer commonly use AAC for streaming music due to its balance of quality and bandwidth efficiency.
• Digital Radio Broadcasting: Standards like DAB+ (Digital Audio Broadcasting) often utilize AAC for transmitting digital radio signals.
• Mobile Devices: AAC is the primary audio codec for devices running iOS and is widely supported on Android devices for music playback and audio recording.
• Online Video Streaming: Many online video platforms, including YouTube and Vimeo, use AAC for the audio tracks in their videos.
• Digital Television: AAC is often used for the audio component of digital television broadcasts, especially for high-definition channels and multi-channel audio.
• Podcasts and Audiobooks: The efficient compression of AAC makes it a popular choice for distributing podcasts and audiobooks.
• Video Game Audio: AAC is used in many video games for background music, sound effects, and dialogue.

Considerations

While AAC is a highly successful codec, there are a few considerations:

• Lossy Compression: As a lossy codec, AAC achieves compression by discarding some audio information deemed less perceptible to human hearing. While generally effective, this process can introduce artifacts, especially at very low bitrates.
• Encoding Quality Variations: The perceived quality of AAC audio can vary depending on the specific encoder used and its settings. High-quality encoders can produce transparent or near-transparent results at reasonable bitrates.

AAC is a highly efficient and widely supported lossy audio codec that delivers excellent audio quality for a broad range of digital media applications. Its dominance in streaming, mobile devices, and digital broadcasting underscores its importance in the modern digital audio landscape. AAC has become the standard for high-quality digital audio and DivX® video supports AAC audio tracks with 5.1 channel surround sound to deliver a cinematic experience – on your computer and on DivX Plus HD and DivX HEVC devices.