Make FLAC files smaller, losslessly or not
This FLAC compressor repacks FLAC files with the reference libFLAC encoder at the compression level you pick, from 0 (fastest) to 8 (smallest). That alone keeps every sample identical — the new file decodes to exactly the same audio, which the tool proves by comparing the MD5 checksum stored in both files. The bigger savings come from changing the audio itself: 24-bit hi-res to 16-bit, 96 or 192 kHz down to 44.1 or 48 kHz, or mono for speech. For a phone or a car, you can also make an MP3 or AAC copy.
Your music is processed in the browser. The tool decodes FLAC itself, checks the stream against its MD5, and encodes with libFLAC 1.4 (BSD licence) compiled to WebAssembly through the MIT-licensed libflacjs wrapper, with libFLAC’s verify mode decoding every frame again as it is written. Vorbis comments, embedded pictures and cue sheets are copied byte for byte.
How to use the FLAC Compressor
- Drop one or more FLAC files on the box. Each row shows the bit depth, length, sample rate, channels, size and whether tags and cover art are present.
- Keep FLAC (lossless) and set the compression level, or pick MP3 or M4A / AAC for a lossy copy.
- Optionally lower the Bit depth, Sample rate or Channels; the plan shows what changes and an estimated size.
- Press Compress. Each file is decoded, checked, encoded and verified; Cancel stops at any time.
- Compare the original and new players, read the check line, and download the files one by one or as a ZIP.
FLAC Compressor features
Levels 0–8 from libFLAC
The same presets as the flac command-line tool, encoded with verify mode on.
Proof it is lossless
When only the level changes, the new STREAMINFO MD5 must equal the original’s; the result says “bit-identical” only when it does.
Hi-res to CD quality
24-bit becomes 16-bit with triangular dither, and 88.2–192 kHz is resampled to 44.1 or 48 kHz with a Kaiser-windowed sinc filter.
Metadata intact
Vorbis comments, pictures, application blocks and cue sheets are copied unchanged (cue sheets only while the sample rate is the same); padding and the old seek table are dropped.
Damaged files caught
Every input is decoded completely and checked against its MD5, so a corrupted FLAC is reported instead of being copied.
What the FLAC compression levels do
All levels are lossless and decode equally fast; higher levels only spend more time searching for a better prediction. Moving from the default 5 to 8 usually saves just a few percent, and a file already made at level 8 may not shrink at all — the tool then tells you to keep the original.
| Level | Block size | Prediction | Stereo |
|---|---|---|---|
| 0 | 1,152 samples | Fixed predictors | Left/right |
| 1–2 | 1,152 samples | Fixed predictors | Mid/side |
| 3 | 4,096 samples | LPC up to order 6 | Left/right |
| 4–6 | 4,096 samples | LPC up to order 8 | Mid/side |
| 7–8 | 4,096 samples | LPC up to order 12 | Mid/side |
Where the real savings are
Strictly, changing bit depth or sample rate alters the audio, so the MD5 changes too; the check line says so. To turn uncompressed recordings into FLAC, use the WAV compressor, and to estimate a whole library first, the audio file size calculator.
- 24-bit to 16-bit. The lowest bits of a 24-bit recording are mostly noise, which FLAC cannot compress, so dropping to 16 bits often cuts the file by a third or more. 16 bits still give 96 dB of dynamic range — more than any home listening room.
- 96 or 192 kHz to 44.1 or 48 kHz. Hi-res sample rates store frequencies far above human hearing; 44.1 kHz covers up to 22 kHz. Choose 44.1 kHz for 88.2/176.4 kHz files and 48 kHz for 96/192 kHz.
- Mono for spoken-word recordings that are stereo only by accident.
- Lossy copies. MP3 at 256 kbps (LAME, LGPL) or AAC at 192 kbps (FFmpeg’s encoder, LGPL) are a fraction of the size and fine for a phone, but keep the FLAC as your master: detail removed by a lossy encoder can never be restored. The MP3 compressor covers bitrates in detail.
FLAC Compressor FAQ
How do I compress a FLAC file without losing quality?
Keep FLAC (lossless) as the output, set the level to 8 and leave bit depth, sample rate and channels on their original settings. The new file is checked against the original MD5 and is bit-identical.
Why did my FLAC barely get smaller?
FLAC is already compressed, and levels differ by only a few percent. If the file was made at a high level, re-encoding can’t gain much. For a large saving, convert 24-bit to 16-bit or lower a hi-res sample rate.
Is this FLAC compressor free and private?
Yes. It costs nothing, needs no sign-up, adds no watermark, and your files never leave your device.
Are tags, album art and cue sheets kept?
Yes. Vorbis comments, embedded pictures and application blocks are copied byte for byte; a cue sheet is kept unless you change the sample rate, because its positions are counted in samples.
Can I convert FLAC to MP3 or AAC here?
Yes. Choose MP3 (lossy) or M4A / AAC (lossy), then a bitrate or target size. Tags and the cover picture are carried into the MP3 or M4A.
Which FLAC files are supported?
Native .flac files up to 24-bit with up to 8 channels. 32-bit FLAC and FLAC inside Ogg containers are not supported.