ALAC (Apple Lossless Audio Codec) — Complete Format Guide
ALAC (Apple Lossless Audio Codec) is a lossless audio compression format developed by Apple Inc. Unlike lossy formats such as MP3 or AAC, ALAC preserves every bit of the original audio signal, making it indistinguishable from the source recording on a technical level. It is the format of choice for Apple's ecosystem — from iTunes and Apple Music to iPhone and AirPlay — and has earned respect in the audiophile community for its transparency and broad native support on Apple hardware.
History of ALAC
Apple introduced ALAC in 2004 as a proprietary format bundled with iTunes 4.5. For seven years it remained closed-source, meaning third-party developers had to reverse-engineer it to add support to non-Apple tools. That changed dramatically in October 2011, when Apple open-sourced the ALAC reference encoder and decoder under the Apache License 2.0, publishing the source code on Google Code (later mirrored to GitHub). This move sparked widespread adoption in open-source media players and converters, placing ALAC on equal legal footing with FLAC.
Despite being open, ALAC has never displaced FLAC as the dominant lossless format outside the Apple ecosystem. FLAC benefits from older, broader toolchain support and is the native lossless format for many streaming services and NAS music servers such as Plex and Navidrome.
File Extension and Container
ALAC audio is stored inside an MPEG-4 container (ISO Base Media File Format), giving it the .m4a file extension — the same extension used by AAC audio files. You can distinguish an ALAC .m4a from an AAC .m4a by inspecting the codec inside: ALAC uses the alac fourCC, while AAC uses mp4a.
Some tools also produce files with the .caf extension (Core Audio Format) when encoding ALAC for Apple-internal use, though .m4a is far more common in practice.
ALAC vs FLAC vs WAV vs AIFF — Lossless Format Comparison
| Feature | ALAC (.m4a) | FLAC (.flac) | WAV (.wav) | AIFF (.aiff) |
|---|---|---|---|---|
| Compression | Lossless | Lossless | None (raw PCM) | None (raw PCM) |
| Typical file size vs WAV | ~50–60% | ~50–60% | 100% (baseline) | ~100% |
| Max bit depth | 32-bit | 32-bit | 32-bit | 32-bit |
| Max sample rate | 384 kHz | 655 kHz | 4.29 GHz (theoretical) | 4.29 GHz (theoretical) |
| Metadata/tags | Yes (iTunes atoms) | Yes (Vorbis comments) | Limited (ID3 optional) | Yes (IFF chunks) |
| Streaming support | Limited | Broad (Tidal, Qobuz) | No | No |
| Apple device native | Yes | No | Partial | Yes |
| Open standard | Yes (since 2011) | Yes | Yes | Yes |
| Software support | Good | Excellent | Universal | Good |
Both ALAC and FLAC achieve roughly 40–50% compression compared to uncompressed PCM (WAV/AIFF). The choice between them is primarily ecosystem-driven: use ALAC for Apple-centric workflows, FLAC for everything else.
Why Apple Uses ALAC
Apple's motivation for creating ALAC was to offer a lossless path within iTunes that integrated seamlessly with the existing MPEG-4 infrastructure it had built around AAC. By using the same .m4a container:
- iTunes could manage lossless and lossy files through the same library engine without major architectural changes.
- iPhone and iPad can play ALAC natively without installing additional codecs, unlike FLAC which required third-party apps until iOS 11 (and even today FLAC support in Apple apps is inconsistent).
- Apple Music Lossless (launched 2021) streams ALAC at up to 24-bit/192 kHz, cementing ALAC as the flagship format for the platform.
- AirPlay 2 transmits ALAC internally, ensuring lossless audio reaches HomePod and Apple TV endpoints.
File Size Comparison: ALAC vs WAV
As a practical reference, a 1-minute stereo recording at 44.1 kHz / 16-bit (CD quality) produces approximately:
- WAV: ~10.1 MB
- ALAC: ~5.5–6.0 MB (roughly 55% of WAV)
- FLAC (level 5): ~5.4–5.9 MB (similar to ALAC)
- MP3 320 kbps: ~2.4 MB (lossy)
For a typical album (45 minutes of music), ALAC saves roughly 200–220 MB compared to WAV while remaining bit-for-bit identical.
Converting ALAC to FLAC with FFmpeg (Lossless)
Since both ALAC and FLAC are lossless, you can convert between them without any quality loss — you are simply repackaging the PCM data:
# Single file: ALAC to FLAC (lossless transcode)
ffmpeg -i input.m4a -c:a flac -compression_level 8 output.flac
# Preserve metadata during conversion
ffmpeg -i input.m4a -c:a flac -compression_level 8 -map_metadata 0 output.flac
# Batch convert all ALAC .m4a files in a folder to FLAC
for f in *.m4a; do ffmpeg -i "$f" -c:a flac -compression_level 8 "${f%.m4a}.flac"; done
The -compression_level 8 flag sets FLAC to its highest standard compression level, producing the smallest files at the cost of slightly longer encoding time. Level 5 is the default and offers a good speed/size balance.
Converting ALAC to MP3
To convert ALAC to MP3 (a lossy format), use the libmp3lame encoder:
# High quality VBR MP3 (recommended)
ffmpeg -i input.m4a -c:a libmp3lame -q:a 2 output.mp3
# Constant bitrate 320 kbps MP3
ffmpeg -i input.m4a -c:a libmp3lame -b:a 320k output.mp3
# Batch conversion
for f in *.m4a; do ffmpeg -i "$f" -c:a libmp3lame -q:a 2 "${f%.m4a}.mp3"; done
Note that converting from ALAC to MP3 introduces permanent quality loss. Always keep the original ALAC file.
Converting FLAC to ALAC
# FLAC to ALAC (lossless — both formats, no quality loss)
ffmpeg -i input.flac -c:a alac output.m4a
# Batch convert FLAC library to ALAC
for f in *.flac; do ffmpeg -i "$f" -c:a alac "${f%.flac}.m4a"; done
Hardware Support
ALAC enjoys native hardware decoding across the entire Apple ecosystem:
- iPhone / iPad — native in the Music app and media framework since iOS 3
- Mac — native in Finder, QuickTime, and all Apple apps
- Apple TV — AirPlay and local playback
- HomePod / HomePod mini — receives ALAC streams via AirPlay 2
- AirPods / Beats — ALAC over AirPlay (not Bluetooth directly)
- Dedicated DACs — Many audiophile USB DACs support ALAC playback through their companion apps or when used with a Mac/iPhone
Non-Apple hardware support is growing but uneven. Most modern Android smartphones and media players do not natively support ALAC, though third-party apps like VLC, Poweramp, and USB Audio Player PRO fill the gap.
Software Support
| Application | Platform | ALAC Support |
|---|---|---|
| iTunes / Music | macOS, Windows | Native |
| VLC | All platforms | Yes |
| foobar2000 | Windows | Yes (plugin) |
| Winamp | Windows | Yes |
| Clementine | Linux/macOS/Windows | Yes |
| Plex Media Server | All platforms | Yes |
| ffmpeg | All platforms | Yes |
| HandBrake | All platforms | Yes (passthrough) |
Summary
ALAC is a mature, open, lossless format that integrates perfectly with the Apple ecosystem. If you store music on an iPhone, use Apple Music, or stream via AirPlay, ALAC is the natural choice. For everything else — cross-platform libraries, streaming services, NAS servers, and audiophile hardware outside Apple's world — FLAC remains the more universal option. Since both formats are lossless, you can convert between them freely without sacrificing a single sample of audio quality.
Related conversions
Audio format pairs that come up most often: