What is ALAC Audio Format? Apple Lossless Audio Codec Explained
Complete guide to ALAC (Apple Lossless Audio Codec), lossless compression format, technical specifications, and applications in Apple ecosystem.
Overview
ALAC (Apple Lossless Audio Codec) is a lossless audio compression codec developed by Apple, introduced in 2004. ALAC compresses audio while maintaining bit-perfect quality—decompressed ALAC is identical to the original uncompressed audio. The codec typically achieves 40-60% file size reduction while preserving all audio information, making it ideal for music libraries where quality is paramount but storage efficiency is desired.
ALAC is stored in the M4A container (MPEG-4 Audio) and is deeply integrated into Apple\s ecosystem, including iTunes, Apple Music, and iOS devices. In 2011, Apple open-sourced ALAC under the Apache License, enabling broader adoption. ALAC competes with FLAC (Free Lossless Audio Codec), which offers similar compression but is more universal across platforms.
Table of Contents
- ALAC Development and Apple Music Strategy - Developer Guide
- ALAC Technical Architecture and Compression Efficiency - Technical Details
- ALAC in Apple Ecosystem - Learn about ALAC in Apple Ecosystem
- ALAC vs FLAC: Comparison and Market Position - View Comparison
- ALAC Applications and Audio Quality - Learn about ALAC Applications and Audio Quality
ALAC Development and Apple Music Strategy
Apple Lossless Audio Codec (ALAC) was developed by Apple and introduced in December 2004 as part of iTunes 4.5. The motivation was to provide Apple customers with a lossless audio option while maintaining efficient file sizes. At the time, lossless audio options were limited: WAV and AIFF were uncompressed and enormous; FLAC was emerging but not universally supported. ALAC filled a niche in the Apple ecosystem.
The codec was proprietary to Apple and closely integrated with iTunes, indicating Apple's commitment to high-quality audio for Mac users. ALAC adoption within Apple ecosystem was strong: iTunes supported ALAC import and playback. iPods supported ALAC (beginning with iPod nano, 2005). Mac OS X included ALAC support in Core Audio framework. However, ALAC remained relatively unknown outside Apple ecosystem due to proprietary nature and limited third-party support.
In February 2011, Apple open-sourced ALAC under the Apache License 2.0, removing licensing barriers. This decision was largely seen as supporting adoption while acknowledging FLAC's dominance in the lossless market. Open-source status enabled broader implementation, though adoption outside Apple ecosystem remains limited. Today, ALAC is standard in Apple Music (the streaming service that replaced iTunes Match). Apple maintains ALAC as the native lossless codec throughout its ecosystem.
ALAC Technical Architecture and Compression Efficiency
ALAC is a lossless compression codec, meaning audio is compressed without any information loss. Decompressed ALAC is identical to the original. Compression Method: Frame-based processing (4096 samples per frame at CD quality). Predictive coding: Predicts each sample based on previous samples. Entropy coding: Uses variable-length codes for efficient storage. Channel Decorrelation: Analyzes left/right channel relationships to improve compression.
Bit Depths Supported: 8-bit, 16-bit (CD quality), 20-bit, 24-bit (professional audio). Sample Rates: Any sample rate from 8 kHz to 384 kHz (encompassing all practical audio). Channels: Mono, stereo, or multi-channel (up to 8 channels). Compression Efficiency: Typical compression: 40-60% file size reduction. A 3-minute CD-quality song uncompressed (50 MB) becomes 20-30 MB in ALAC. Variation by content: Speech compresses better than music (60-70% reduction possible).
Classical music compresses less (30-40% reduction typical). The algorithm adapts to content characteristics for optimal compression. Quality: Perfect lossless quality maintained regardless of compression ratio. All original audio information preserved exactly.
