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Compress FLAC files

Make FLAC music smaller for your phone, or learn what lossless re-encoding can save.

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How to compress FLAC files

  1. Add your files

    Drop files on the box, paste them or choose them from your device. Nothing is uploaded.

  2. Check the settings

    The default preset suits most files. Change quality, size or format if you need a smaller file.

  3. Download the result

    Save each file or all of them as one ZIP. If a file cannot get smaller, you keep the original.

FLAC: lossless audio that is still compressed

FLAC (Free Lossless Audio Codec) was first released in 2001 and is maintained by the Xiph.Org Foundation. It works like ZIP for sound: decoding a FLAC file gives back exactly the samples of the original recording, bit for bit, yet the file is considerably smaller than a WAV. It is royalty-free, supports bit depths up to 32 bits and very high sample rates, and is the standard format for lossless music downloads, CD rips and high-resolution audio stores.

FLAC files are big compared with lossy formats. A CD-quality album of 45 minutes is typically a few hundred megabytes in FLAC, against about 43 MB as a 128 kbps MP3. A 24-bit, 96 kHz download can easily pass a gigabyte.

How FLAC compresses, and why levels barely matter

FLAC splits audio into blocks, predicts each sample from the previous ones with a linear predictor, and stores only the difference between prediction and reality using Rice codes. It also exploits the similarity of left and right channels. Quiet passages, silence and simple sounds are predicted well and shrink a lot; loud, dense, noisy masters shrink less.

The compression level (0 to 8 in the reference encoder) only controls how hard the encoder searches for good predictors. Higher levels take longer to encode and produce slightly smaller files; decoding speed is almost the same at every level. Re-encoding a FLAC that was saved at level 0 or by a fast ripper can therefore save some space without any change to the sound, but usually only a few percent. This tool has no level setting: when FLAC stays FLAC, it re-encodes the audio and returns your original if the result is not smaller.

Ways to make a FLAC file smaller

MethodLossless?Effect on size
Re-encode FLAC at a higher levelYesSmall
Remove a large embedded cover imageYes (the audio is untouched)Small to moderate, depending on the artwork
Reduce 24-bit to 16-bit and 96 kHz to 44.1 or 48 kHzNo, but inaudible on normal equipmentLarge: a 24/96 file becomes roughly a third of its size
Convert to AAC, Opus or MP3NoVery large: typically several times smaller, even at generous bitrates

Which route is right depends on why the file must shrink:

  • Copying music to a phone: AAC at 192 kbps or Opus at 128–160 kbps. Keep the FLAC as your master copy on a computer or drive.
  • Sending a mix to someone for review: a 256 kbps lossy file is fine for listening; send FLAC only if they will process the audio further.
  • Archiving: stay with FLAC. Never replace the only lossless copy with a lossy one.

Compatibility and pitfalls

  • Apple devices. Current iPhones, iPads and Macs play FLAC, but Apple's own library tools prefer ALAC, the Apple Lossless format in an M4A file. Very old iPods and some car systems do not play FLAC at all.
  • Tags and artwork. FLAC uses Vorbis comments and embedded pictures. The tool keeps tags and cover art by default; turn the option off if a large embedded scan of the booklet makes the files heavy.
  • 24-bit files come out at 16 bits. The FLAC tool writes FLAC at 16-bit by default, which is CD resolution; in our tests, a 24-bit, 96 kHz test file went from 18.9 MB to 8.6 MB that way. Choose "Keep original" under Bit depth for a bit-exact copy of a high-resolution file.
  • "Hi-res" with no real benefit. Some 24-bit files are simply upsampled CD audio. Converting them to 16-bit, 44.1 kHz loses nothing that was really there.

FLAC questions

Is FLAC really lossless?

Yes. Each frame even carries a checksum, and the file stores an MD5 signature of the original audio, so a decoder can verify that the output matches exactly.

Can I convert FLAC to MP3 and back without loss?

No. Once converted to MP3, the discarded information is gone. A FLAC made from an MP3 is lossless only relative to the MP3, and much bigger than it.

FLAC or WAV for recording?

The sound is the same. WAV is simpler for editing software; FLAC saves space and supports tags, which makes it better for storage.

Which lossy bitrate sounds like FLAC?

For most people, AAC at 256 kbps or Opus at 160 kbps is indistinguishable in blind listening. Try a passage you know well on your own headphones.

Related pages

Start from WAV if your recording is uncompressed, or go to the audio compressor. The difference between lossless and lossy is explained in how it works.