ALAC vs FLAC: Apple Lossless, Explained

If you've ever bought lossless music from one store and ripped a CD with a different program, there's a decent chance you now own two flavours of "lossless": some files ending in .flac and some ending in .m4a. The second kind is usually ALAC, Apple Lossless Audio Codec. People ask which one is better. The honest answer is that neither sounds better, and the interesting differences are everywhere except the sound.

The part that doesn't differ: the audio

Both FLAC and ALAC are lossless. Decode an ALAC file and you get the original PCM samples back, bit for bit. Decode a FLAC of the same recording and you get the exact same samples. Play both and you are listening to the identical stream of numbers. There is no "ALAC sound" and no "FLAC sound", any more than a document has a different meaning depending on whether you zipped it or rar'd it.

That also means converting between them is free. FLAC to ALAC to FLAC again, a hundred times, and the audio is untouched. If you're unsure, you can prove it: decode both to WAV and compare the files. They match. (If you want the grounding on why lossless works this way, the plain-English FLAC guide covers it.)

Choosing between ALAC and FLAC is not a sound-quality decision. It's a decision about where your music has to play and how well the file looks after itself.

Where they came from

FLAC appeared in 2001, joined the Xiph.Org Foundation in 2003 (the same non-profit behind Ogg Vorbis and Opus) and has been open, patent-free and freely licensed from the start. That openness is why it turned up everywhere: Linux players, Android, hardware streamers, CD rippers, download stores, car stereos.

ALAC was Apple's answer in 2004, designed for iTunes and the iPod at a time when Apple had no interest in supporting someone else's codec. For years it was closed and reverse-engineered by outsiders. In 2011 Apple open-sourced it under the Apache 2.0 licence, which is why non-Apple software can legally decode it today. Apple Music's lossless tier, launched in 2021, streams in ALAC.

So both are open now. FLAC simply had a decade's head start on the rest of the world, and Apple had a decade's head start on Apple.

Compression: a near tie

FLAC generally compresses a little tighter, typically a few percent smaller than ALAC for the same album. On a 30 GB library that's maybe a gigabyte. It's a real difference, but not one that should decide anything on its own. Both land in the same neighbourhood: roughly half the size of the uncompressed WAV.

Error checking: FLAC's quiet advantage

This is the difference that matters most for an archive, and it's the one almost nobody talks about.

A FLAC file stores an MD5 checksum of the original, unencoded audio in its header, and every audio frame carries its own CRC. That means a FLAC file can be tested. Run it through the decoder and it will tell you, definitively, whether the audio inside is exactly what was encoded years ago or whether a bit has flipped somewhere along the way.

ALAC, living inside an MP4 container, has no equivalent. A damaged ALAC file usually just plays with a click, a dropout or a burst of noise, and nothing in the file can tell you it's wrong. For music you intend to keep for decades, self-verifying files are worth having, and that's a big part of a sane backup strategy.

Tagging: two different traditions

FLAC uses Vorbis comments: a free-form list of KEY=value pairs. Any tag you can name is allowed, multiple values per field work naturally (two genres, three artists), and every serious tagger speaks it fluently. It's the more flexible system, and the more consistent one across software.

ALAC uses the MP4 atom system that iTunes built. It handles the essentials well and has good support for things Apple cares about, like gapless information and album artist, but it's a fixed vocabulary with an escape hatch for custom fields that different programs read differently. If you've ever had a tag show up in one app and vanish in another, this is usually why. Metadata is what makes a library searchable, so the more predictable system has real value.

Compatibility: the actual deciding factor

Here is the one place they genuinely diverge.

• Inside Apple's world, ALAC is native. iTunes and the Music app have handled it for two decades; iPhones play it without a second thought. Apple did eventually add FLAC support (iOS 11 and macOS High Sierra in 2017), but it lives in the Files app and Safari rather than the Music app, which still won't import a FLAC.
• Everywhere else, FLAC is the default and ALAC is the guest. Most Android players, Linux tools, streamers and car systems handle FLAC first. Many do support ALAC too, but it's the format you have to check for rather than the one you can assume.
• In a browser, FLAC decodes natively in every major engine. ALAC support is essentially a Safari feature; Chrome and Firefox don't ship a decoder for it.

So which one should you keep?

A simple rule that works for nearly everyone:

1. Archive in FLAC. It's the universal, self-checking, better-tagged, slightly smaller option. If a rip or a purchase arrives as ALAC, converting it to FLAC once loses nothing and gives you a master file that will still be readable in thirty years on any system.
2. Convert to ALAC only for the devices that demand it. If your daily listening runs through the Apple Music app on a phone, make ALAC copies for that library and leave the FLAC masters where they are. The conversion is lossless, so nothing is at stake.
3. Never keep both as "the master". Two copies of the same album in two lossless formats is the fastest way to lose track of which one has the corrected tags. Pick one canonical copy and derive the other.

If your entire life is Apple and you never touch anything else, ALAC-only is perfectly fine. Just know that you're choosing convenience over verifiability, and keep a real backup because your files can't tell you when they've been hurt.

Converting without breaking anything

Any competent tool will do this losslessly: ffmpeg, XLD on the Mac, dBpoweramp or foobar2000 on Windows. Two things to check when you convert:

• Tags carry over. Most converters map the common fields correctly, but look at a few albums afterwards, particularly album artist, disc number and anything multi-valued.
• The art comes with it. Embedded cover art sometimes gets dropped in the conversion. Check a handful of albums before you delete the originals.

And when you're done, test the new FLACs. That built-in checksum is only useful if you actually use it.

Not sure what's inside your M4A files? Open the player, drop one in, and the codec readout will tell you whether it's ALAC or plain AAC.