What Is ALAC? Apple Lossless Audio Codec Explained

ALAC stands for Apple Lossless Audio Codec. It is Apple's answer to FLAC -- a lossless compression format that shrinks audio files without removing any data. Decoding an ALAC file gives you identical audio to the original uncompressed WAV.

ALAC and M4A: The Connection

ALAC files use the .m4a extension -- the same extension as AAC files. This confuses people. How do you tell them apart?

Check the file details. In macOS Finder, right-click > Get Info > More Info. You will see Apple Lossless or ALAC for lossless files, and AAC for compressed files. The bitrate is also a giveaway: ALAC files show 400-1,400 kbps depending on content complexity. AAC typically sits between 96-320 kbps.

How ALAC Compresses Audio

ALAC uses a linear prediction model similar to FLAC. It predicts the next audio sample based on previous samples, stores the prediction, and records only the error. The decoder reverses this process to reconstruct perfect audio.

Typical compression ratio: ALAC files are about 40-60% the size of equivalent WAV files. The same as FLAC. A 40 MB WAV becomes roughly 22-28 MB in ALAC.

ALAC vs FLAC

Both are lossless. Decoded audio is identical. The differences:

Compatibility:

ALAC: Native on all Apple devices and software (iPhone, Mac, Apple TV, Logic Pro, GarageBand). Also supported on Windows via iTunes/Apple Music.

FLAC: Native on Android, Linux, most portable audio players. Limited native Apple support until recent macOS/iOS versions added basic FLAC playback.

Apple Music Lossless

Apple Music added lossless audio streaming in 2021. The library streams as ALAC at 44.1 kHz / 16-bit (CD quality) for standard lossless. Hi-Res Lossless goes up to 192 kHz / 24-bit ALAC.

When to Use ALAC

Use ALAC when:

You are in an Apple-centric workflow (Logic Pro, GarageBand, iPhone, Mac)

You want lossless files that your Apple devices handle natively

You are backing up your iTunes/Apple Music library

Use FLAC instead when:

You use Android, Linux, or mixed platforms

You use a dedicated portable audio player

You want maximum software compatibility across all platforms

Converting ALAC Files

ALAC to FLAC conversion is lossless -- you are just changing the container, not the audio quality. ALAC to MP3 is a lossless-to-lossy conversion. Use 256 or 320 kbps MP3 to preserve as much quality as possible from the lossless source.