Audio Format Comparison

ALAC vs M4A — Apple Lossless vs Apple AAC

ALAC and M4A both commonly use the .m4a extension, which causes confusion. M4A typically refers to AAC audio (lossy, compressed) inside an MPEG-4 container. ALAC is Apple Lossless Audio Codec — also stored in .m4a or .alac files. Both are 'M4A' files; the codec inside determines whether it's lossless or lossy.

ALACvsM4A

Quick Verdict

Use ALAC when…

Use ALAC (lossless M4A) for archival and high-fidelity listening on Apple devices. ALAC preserves every audio sample exactly, with file sizes around 50% of WAV.

Use M4A when…

Use AAC (lossy M4A) for portable music, streaming, and storage-constrained playback. AAC at 256 kbps sounds excellent on most equipment and uses 1/4 the storage of ALAC.

ALAC vs M4A: Feature Comparison

Feature	ALAC	M4A
Compression	Lossless	Lossy (AAC)
File extension	.m4a or .alac	.m4a
Audio quality	Bit-perfect identical to source	Excellent at 256+ kbps
File size (4 min track)	~25 MB	~8 MB at 256 kbps
Apple Music streaming	Hi-Fi tier delivery	Standard delivery
iPhone/iOS support	Native	Native

When ALAC wins

✓Compression: Lossless
✓File extension: .m4a or .alac
✓Audio quality: Bit-perfect identical to source

When M4A wins

✓Compression: Lossy (AAC)
✓File extension: .m4a
✓Audio quality: Excellent at 256+ kbps

Frequently asked questions

How do I tell if an M4A file is ALAC or AAC?

Right-click in Finder → Get Info → check 'Kind' (shows 'Apple Lossless audio file' for ALAC, 'AAC audio file' for AAC). Or use FFprobe: `ffprobe input.m4a 2>&1 | grep Audio` — shows 'alac' for ALAC, 'aac' for AAC.

Can I convert ALAC to AAC inside the same M4A file?

Technically yes — re-encode the audio: `ffmpeg -i input-alac.m4a -c:a aac -b:a 256k output-aac.m4a`. The result is a smaller file, but you've lost lossless quality permanently. For playback flexibility, keep an ALAC master and create AAC copies for portable devices.