What is a FLAC file? The lossless audio format explained

Most of us grew up with MP3s. You ripped a CD, set the bitrate to 128 or 320, and the song shrank to a few megabytes that fit on any device. It played everywhere, it sounded good enough, and you could lock the quality in forever.

Then you buy an album on Bandcamp, select the highest quality download option, and end up with a folder of .flac files that are three or four times the size of a high-bitrate MP3. You open it in Apple Music, and nothing happens; you choose the Files app, and it plays fine. 

Are you confused? Understandable. FLAC is the format archivists, labels, and people who actually care about the original recording rely on. But it’s also the format most likely to make your phone act like it’s never seen a music file.

Here’s what FLAC actually is, why the files are relatively large, and how to handle them on a phone.

What does FLAC stand for?

FLAC stands for Free Lossless Audio Codec. Let’s break it down word for word.

Free means truly free. FLAC was created by the Xiph.Org Foundation, the non-profit organization behind Vorbis and Opus, and the format is free of patents or licensing fees. Everyone can create software that encodes or decodes FLAC without paying anyone. That’s why libraries, national archives, and labels standardized on it.

Lossless means you can reverse the compression. If you decode a FLAC file, you’ll get back a bit-for-bit identical copy of the audio that went in.

Codec is shorthand for coder-decoder: the piece of software that compresses or decompresses digital media. A codec and a file format aren’t the same thing, although people use the words interchangeable and they nearly are, and for FLAC the codec and the .flac container are the same name.

How lossless compression actually works

“Compression” confuses people because most of us learned it from MP3 and JPEG, where it means quality is lost.

Lossy compression (the MP3 method) discards parts of the signal you probably won’t notice: sounds above your hearing range, quiet sounds, stereo nuances. That’s how a 40 MB song can be compressed into a 4 MB song.

FLAC works more like a ZIP file on a spreadsheet. It looks for mathematical patterns in the waveform and describes them more efficiently. The encoder fits a prediction model to short blocks of audio, stores the model plus the difference between the prediction and the real signal, then packs that difference tightly. Run it back through a decoder and the original samples reappear perfectly.

Music is complex, so there’s a limit to how much you can squeeze. A text file can be compressed by ZIP to about 10% of original file size as text contains lot of repetitive characters unlike audio. 

Xiph.Org’s own numbers show ZIP managing 20-40% on a CD-quality file while FLAC reaches 30-70%, because it was built specifically for sound. 

FLAC file size: the numbers

Let’s do the arithmetic properly. Standard CD audio is 16-bit, 44.1 kHz, stereo. Multiply it out and you get a data rate of 1,411 kbps, or about 176 KB every second. That’s the raw, uncompressed number that a WAV or AIFF file stores. 

For a four-minute track:

So, a pop song of about 3 minutes would have an average FLAC file size of about 25 MB, which means 5 to 7 MB approx per minute. 300 MB for a 50-min album, 530 MB as WAV, 120 MB as a high-bitrate MP3. 

Hi-res files are different. A 24-bit, 96 kHz stereo recording carries 4,608 kbps uncompressed, and dense high-resolution audio tends to compress less efficiently than CD material, because there’s more genuine high-frequency content and less silence to exploit. A four-minute hi-res track can easily land between 70 and 100 MB. An album of those will take a bite out of a 128 GB phone.

Two things affect that number. Quiet, sparse recordings compress well: solo piano, ambient, spoken word. Loud, dense, heavily compressed modern masters compress badly, sometimes barely reaching 75% of the WAV. And bit depth matters more than you’d expect, because the least significant bits of a 24-bit recording are close to random noise, and noise doesn’t compress.

Picking the right output format

MP3 is the answer when compatibility is the only concern. Nothing made in the past 25 years refuses an MP3. Use 320 kbps if you want the conversion to be as close to inaudible as it gets, 192 to 256 kbps for everyday listening, and 128 kbps only when the target device is genuinely short on space. A 25 MB FLAC becomes roughly a 9.6 MB MP3 at 320 kbps or 3.8 MB at 128 kbps. 

M4A/AAC is the better choice when it comes to Apple devices in particular. At that same bitrate, AAC usually sounds better than MP3, and it drops right into Apple Music without any problems. It’s also the format to use if you’re creating a ringtone. 

WAV is only worth it when you need it for a specific software, which is generally older video editing or DJ software. It’s lossless but approximately twice as large as the FLAC you began with, which is pointless for most people.

One rule regardless of what you pick: keep the original FLAC files somewhere. MP3 and AAC are one-way conversions, but converting back to FLAC afterwards produces a large file containing lossy audio.

How to play FLAC files

Now, FLAC is almost universally supported.

On Windows

Windows has decoded FLAC natively since Windows 10. All you need is to double-click a .flac and Windows will open it in Media Player. 

If you want a music library rather than a file that plays, use foobar2000 or VLC.

On Mac

QuickTime doesn’t play FLAC, the Music app won’t import it, and Finder will only show you the metadata.

Everything else works fine. VLC and IINA both play FLAC without setup, and IINA in particular feels like a native Mac app rather than a port. If you’d rather live inside Apple Music, convert your library to ALAC once and be done with it.

On Android 

Android supports FLAC natively from version 3.1, and most third-party players such as VLC, Poweramp and Musicolet support it by default. Drag files onto the device over USB and they show up in your music app.

On iPhone

Your iPhone hardware decodes FLAC perfectly as well. Apple added support in iOS 11 and lists it in the specs. What Apple did not do is let the Music app import it. 

So, you can play it from Files, convert to ALAC (another lossless format) or use an app that handles FLAC properly.

How to convert FLAC to MP3 with Documents.io

If you want your music to work everywhere, in the car, on an old iPod, in a video editor, on a running watch with 8 GB of storage, the best approach is to convert it.

Documents.io does it in the browser. There’s nothing to install, it runs the same on an iPhone as it does on a Mac or a Linux desktop, and the files are stored for a maximum of four hours before being deleted. Free accounts get up to 10 conversions, which is plenty for a handful of tracks.

Just open the FLAC converter and drag your files in, then select your output format, and hit Convert. Wait for the site to process your files and download the results.

FAQ

Is FLAC better than MP3?

For quality and archiving, yes. FLAC preserves the recording exactly, and MP3 permanently discards parts of it. For everyday listening, most people can’t reliably tell a difference between MP3 and FLAC, and the MP3 is much smaller.

Does converting FLAC to MP3 lose quality?

Yes, because MP3 is lossy. At 256 kbps or higher the difference is inaudible to most listeners on most equipment, but it’s permanent, so keep the FLAC originals.

Why is my FLAC file so large?

Because it’s storing the entire recording rather than an approximation of it. If a specific file seems unusually big even for FLAC, check the bit depth and sample rate in its properties: a 24-bit, 96 kHz file carries more than three times the data of a standard CD-quality one.

What opens a .flac file on Windows or Mac?

VLC and foobar2000 handle FLAC on both. Windows Media Player has supported it since Windows 10, and on macOS, QuickTime does not, but VLC, IINA, and Music (after conversion to ALAC) do.