Lossy or lossless: which audio format should I keep my library in?

For long-term archiving choose FLAC (lossless, ~50% the size of WAV). For everyday listening on phones and streaming use MP3 320 kbps or Opus 192 kbps (transparent quality, no audible difference at normal volumes). Avoid converting lossy → lossy → lossy: every step compounds artifacts.

Lossy or lossless: which audio format should I keep my library in?

For long-term archiving choose FLAC (lossless, ~50% the size of WAV). For everyday listening on phones and streaming use MP3 320 kbps or Opus 192 kbps (transparent quality, no audible difference at normal volumes). Avoid converting lossy → lossy → lossy: every step compounds artifacts.

Guide

M4A Format: MPEG-4 Audio — Apple Lossless, AAC & iTunes Explained

PC By Pablo Cirre • Updated May 7, 2026

M4A (MPEG-4 Audio) — Complete Format Guide

What Is M4A?

M4A is a file extension used by Apple to identify MPEG-4 audio files stored in the MPEG-4 container (ISO Base Media File Format, ISOBMFF). The .m4a extension is Apple's convention for distinguishing audio-only MPEG-4 files from video-containing .mp4 files — both use the identical container format internally.

M4A files can contain one of two fundamentally different audio codecs:

AAC (Advanced Audio Coding) — lossy compression; smaller files; iTunes Store downloads and Apple Music streaming
ALAC (Apple Lossless Audio Codec) — lossless compression; larger files; identical quality to WAV/FLAC; used in Apple Music Lossless tier

Despite identical file extensions, M4A-AAC and M4A-ALAC are very different in quality and file size. Most .m4a files encountered in practice are AAC-encoded.

MPEG-4 Container (ISOBMFF) Structure

M4A uses the same ISO Base Media File Format as MP4 video:

ftyp   — File type box ('M4A ', 'mp42', 'isom' compatibility)
moov   — Movie box (metadata)
  ├─ mvhd  — Movie header (duration, time scale)
  ├─ trak  — Audio track
  │   ├─ tkhd — Track header
  │   └─ mdia — Media box
  │       ├─ mdhd — Media header (language, timescale)
  │       ├─ hdlr — Handler ('soun' = sound track)
  │       └─ minf — Media information
  │           └─ stbl — Sample table (sample locations, sizes, timestamps)
  ├─ udta  — User data (iTunes metadata)
  └─ meta  — Metadata container (iTunes tags in 'ilst' box)
mdat   — Media data (compressed audio samples)

The ftyp box identifies M4A files with brand M4A (including the trailing space). This tells audio players to expect audio-only MPEG-4 content.

M4A-AAC: Apple's Standard Audio Format

iTunes Store History

Apple launched the iTunes Music Store in April 2003 using AAC (128 kbps initially, upgraded to 256 kbps AAC in 2009 with "iTunes Plus" — DRM-free). AAC was chosen because:

Superior audio quality vs. MP3 at equal bitrates
MPEG-4 standard (open specification, not Fraunhofer-proprietary like MP3)
Apple's hardware (iPod, iPhone) included dedicated AAC decoder chips
Apple was involved in developing the MPEG-4 standard

Apple Music Streaming Bitrates

Apple Music streams at:

Standard quality: 256 kbps AAC (lossy)
High-quality: 256 kbps AAC (same; "High Quality" refers to AAC vs. lower-bitrate alternatives)
Lossless: ALAC at 16-bit/44.1 kHz (~1,000 kbps equivalent) or 24-bit/48 kHz
Hi-Res Lossless: ALAC at 24-bit/96 kHz or 24-bit/192 kHz (~3,700 kbps)

DRM in M4A (FairPlay)

iTunes Store M4A files purchased before 2009 use FairPlay DRM — Apple's proprietary encryption. FairPlay-protected M4A files:

Play only in iTunes/Apple Music and authorised devices (up to 5 Macs, unlimited iOS devices)
Cannot be converted by third-party tools
Are region-locked to the iTunes Store they were purchased in
Cannot be played on non-Apple players (Spotify, Amazon Music, etc.)

Since the "iTunes Plus" launch in 2009, all new iTunes Store purchases are DRM-free 256 kbps AAC. Legacy DRM content can be upgraded to DRM-free via Apple's upgrade program.

M4A-ALAC: Apple Lossless Audio Codec

Apple developed ALAC internally and released it open-source under Apache 2.0 licence in October 2011. ALAC provides:

Lossless compression: identical audio data to WAV/AIFF, bit-for-bit
Compression ratio: 40–60 % size reduction vs. uncompressed WAV (comparable to FLAC)
Bit depths: 16-bit, 20-bit, 24-bit, 32-bit
Sample rates: up to 384,000 Hz
Channels: up to 8 channels (7.1 surround)

ALAC vs. FLAC

Feature	ALAC (M4A)	FLAC
Container	MPEG-4 (M4A)	Native FLAC or Ogg
Apple native	Yes — plays in iTunes, iPhone, Apple TV	Requires app on iOS
Android native	Limited	Yes (most players)
Windows native	Via Apple Music / iTunes	Via codec or VLC
Compression	40–60 %	40–60 %
Metadata	iTunes tags (ilst box)	Vorbis Comments
Gapless playback	Full support	Full support
Streaming	Apple Music Lossless	Tidal, Qobuz

ALAC's primary advantage over FLAC is seamless Apple ecosystem integration — every Apple device plays ALAC natively without additional codecs. FLAC requires VLC or third-party apps on iOS.

iTunes Tags: M4A Metadata

iTunes uses a proprietary but well-documented tagging system within the MPEG-4 ilst box:

Tag Atom	Meaning
`©nam`	Title
`©ART`	Artist
`©alb`	Album
`©day`	Year
`©gen`	Genre
`trkn`	Track number / total tracks
`disk`	Disc number / total discs
`©wrt`	Composer
`©lyr`	Lyrics
`©cmt`	Comment
`cprt`	Copyright
`covr`	Cover art (JPEG or PNG embedded)
`aART`	Album artist
`tmpo`	BPM (tempo)
`©grp`	Grouping
`soal`, `soar`, `sosn`	Sort keys for Album, Artist, Song

M4A metadata is more structured than ID3 (MP3 metadata), supporting full sort-key fields that enable proper alphabetical sorting in large libraries even when display names start with "The" or "A".

File Size Comparison

For a 3-minute stereo song:

M4A-AAC (128 kbps): ~2.9 MB
M4A-AAC (256 kbps): ~5.8 MB (Apple Music standard)
M4A-ALAC (44.1 kHz/16-bit): ~20–30 MB (typical)
M4A-ALAC (96 kHz/24-bit Hi-Res): ~60–90 MB
WAV (44.1 kHz/16-bit): ~30.5 MB
MP3 (320 kbps): ~7.2 MB
FLAC: ~18–22 MB

Converting M4A Files

M4A-AAC → MP3

Common for compatibility with non-Apple players:

Always involves re-encoding (both are lossy); generation loss applies
Use highest available quality settings (MP3 320 kbps CBR)
Source from the highest-bitrate M4A available to minimise transcoding degradation
If you have the original lossless source, encode MP3 from that instead

M4A-AAC → FLAC

Technical lossless conversion of a lossy source:

FLAC preserves the AAC-decoded PCM exactly (no further loss)
File is larger than AAC but still contains the AAC compression artefacts
Useful for library standardisation where all files must be FLAC regardless of source quality

M4A-ALAC → FLAC

True lossless-to-lossless conversion:

Audio data is mathematically identical in both formats
Useful for cross-platform sharing where FLAC has better support than ALAC
No quality change whatsoever

M4A-ALAC → WAV

Decompression of lossless data:

Produces bit-for-bit identical PCM to the original recording
Useful for DAW import, CD burning, hardware device compatibility
File sizes increase to full WAV dimensions

DRM-Protected M4A

Cannot be converted by any tool. Options:

Upgrade via Apple (DRM-free purchase or Apple Music subscription)
Use Apple's authorised playback ecosystem

Platform Support for M4A

Platform	AAC Support	ALAC Support
iOS / iPadOS	Native	Native
macOS / Apple TV	Native	Native
Windows	Via iTunes / Apple Music app	Via iTunes / Apple Music app
Android	AAC native; ALAC via VLC	VLC required
Linux	Via ffmpeg, VLC, gstreamer	Via ffmpeg, VLC, gstreamer
Web browsers	AAC: Yes; ALAC: No	No native
Amazon Echo	AAC: Yes	No
Sonos	AAC: Yes	Yes (ALAC supported)

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Audio format pairs that come up most often:

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Frequently Asked Questions

M4A (AAC) and MP3 are both lossy audio formats, but AAC delivers better audio quality at the same file size. A 256 kbps M4A-AAC sounds noticeably better than a 256 kbps MP3. M4A also has better metadata support (album art, sort fields, lyrics). The main MP3 advantage is slightly broader compatibility with very old hardware.

M4A (AAC) e MP3 are both com perdas audio formatoos, mas AAC delivers better qualidade do áudio at the same tamanho do arquivo. A 256 kbps M4A-AAC sounds noticeably melhor que a 256 kbps MP3. M4A also has better metadata support (album art, sort fields, lyrics). The main MP3 advantage is slightly broader compatibilidade com very old hardware.

M4A (AAC) und MP3 are both verlustbehaftet audio Formate, aber AAC delivers better Audioqualität at the same Dateigröße. A 256 kbps M4A-AAC sounds noticeably besser als a 256 kbps MP3. M4A also has better metadata support (album art, sort fields, lyrics). The main MP3 advantage is slightly broader Kompatibilität mit very old hardware.

M4A (AAC) y MP3 are both con pérdidas audio formatoos, pero AAC delivers better calidad de audio at the same tamaño de archivo. A 256 kbps M4A-AAC sounds noticeably mejor que a 256 kbps MP3. M4A also has better metadata support (album art, sort fields, lyrics). The main MP3 advantage is slightly broader compatibilidad con very old hardware.

For long-term archiving choose FLAC (lossless, ~50% the size of WAV). For everyday listening on phones and streaming use MP3 320 kbps or Opus 192 kbps (transparent quality, no audible difference at normal volumes). Avoid converting lossy → lossy → lossy: every step compounds artifacts.

It depends on the codec inside. M4A-AAC is lossy (like MP3) — it permanently discards audio information to reduce file size. M4A-ALAC is lossless — the audio is mathematically identical to the original WAV or FLAC source. Apple Music Lossless streams ALAC inside M4A containers.

Depende de the codec inside. M4A-AAC is com perdas (like MP3) — it permanently discards audio information to reduce tamanho do arquivo. M4A-ALAC is sem perdas — the audio is mathematically identical para o original WAV ou FLAC source. Apple Music sem perdas streams ALAC inside M4A containers.

Es hängt ab von the Codec inside. M4A-AAC is verlustbehaftet (like MP3) — it permanently discards audio information to reduce Dateigröße. M4A-ALAC is verlustfrei — the audio is mathematically identical zum original WAV oder FLAC source. Apple Music verlustfrei streams ALAC inside M4A Containers.

Depende de the codec inside. M4A-AAC is con pérdidas (like MP3) — it permanently discards audio information to reduce tamaño de archivo. M4A-ALAC is sin pérdidas — the audio is mathematically identical al original WAV o FLAC source. Apple Music sin pérdidas streams ALAC inside M4A contenedors.

Spoken-word podcasts: 44.1 kHz mono, 64–96 kbps Opus or 96 kbps MP3. Music podcasts: 44.1 kHz stereo, 128–192 kbps. Going above wastes bandwidth — speech has limited frequency content above 7 kHz, and listeners on data plans appreciate the smaller file. Apple Podcasts and Spotify both accept up to 48 kHz / 320 kbps.

Not directly on iPhone without a third-party app. On a Mac, GarageBand or iTunes/Apple Music can export M4A as MP3. On Windows, iTunes converts M4A to MP3 via Preferences > Import Settings. Online converters and KaijuConverter convert M4A to MP3 directly in the browser without software installation.

Not directly no iPhone sem a third-party app. em um Mac, GarageBand ou iTunes/Apple Music can export M4A as MP3. no Windows, iTunes converts M4A to MP3 via Preferences > Import Settings. Online converters e KaijuConverter converter M4A to MP3 directly in o navegador sem software installation.

Not directly auf iPhone ohne a third-party app. auf einem Mac, GarageBand oder iTunes/Apple Music can export M4A as MP3. auf Windows, iTunes converts M4A to MP3 via Preferences > Import Settings. Online converters und KaijuConverter umwandeln M4A to MP3 directly in der Browser ohne Software installation.

Not directly en iPhone sin a third-party app. en un Mac, GarageBand o iTunes/Apple Music can export M4A as MP3. en Windows, iTunes converts M4A to MP3 via Preferences > Import Settings. Online converters y KaijuConverter convertir M4A to MP3 directly in el navegador sin software installation.

Lossy → lossy compounds quantization noise. Each encode discards the same kind of perceptual information again, multiplying artifacts. Always re-encode from a lossless master if you have one (WAV, FLAC, or the original recording). If only an MP3 is available, keep the bitrate at or above the source — never go up to "improve quality".

For lossless quality: M4A-ALAC at 24-bit/96 kHz or higher (Apple Music Hi-Res Lossless tier). For lossy quality: 256 kbps AAC (Apple Music standard) is transparent for most listeners. For universal compatibility: 256 kbps AAC; for professional archival: ALAC or FLAC lossless.

For sem perdas quality: M4A-ALAC at 24-bit/96 kHz ou altaer (Apple Music Hi-Res sem perdas tier). para com perdas quality: 256 kbps AAC (Apple Music padrão) is transparente para most listeners. para universal compatibilidade: 256 kbps AAC; para profissional archival: ALAC ou FLAC sem perdas.

For verlustfrei quality: M4A-ALAC at 24-bit/96 kHz oder hocher (Apple Music Hi-Res verlustfrei tier). für verlustbehaftet quality: 256 kbps AAC (Apple Music Standard) is transparent für most listeners. für universell Kompatibilität: 256 kbps AAC; für professionell archival: ALAC oder FLAC verlustfrei.

For sin pérdidas quality: M4A-ALAC at 24-bit/96 kHz o altaer (Apple Music Hi-Res sin pérdidas tier). para con pérdidas quality: 256 kbps AAC (Apple Music estándar) is transparente para most listeners. para universal compatibilidad: 256 kbps AAC; para profesional archival: ALAC o FLAC sin pérdidas.

Most modern tools (FFmpeg with <code>-map_metadata 0</code>, foobar2000, dBpoweramp) preserve ID3 tags and embedded cover art. Some quick-and-dirty converters strip them silently. KaijuConverter preserves tags in its <a href="/convert/flac-to-mp3">audio conversions</a>; if metadata is critical to you, verify the output with <code>ffprobe</code> before deleting the original.