Tool guide
WAV stores audio with no compression at all, so a minute of 44.1 kHz stereo takes about 10 megabytes. FLAC compresses an integer signal losslessly: the file roughly halves and decoding returns bit-for-bit identical audio. libFLAC compiled to WebAssembly does the encoding on the page, and the WAV header is read directly, so the sample rate survives without resampling. One exception: 32-bit float is written as 24 bits, and the status line says so. See also: a light MP3 copy for sending and posting, lossy AAC compression for phone playback, a quick sound check after converting.
For an integer WAV, yes: decoding returns exactly the same stream of samples, down to the last bit. The difference from MP3 and AAC is that those discard information permanently, which is why FLAC is used for archives and masters. The exception is 32-bit float: FLAC does not store that depth, so the signal is written as 24 bits, values outside the range are clipped, and the page reports how many alongside a warning that this is not a bit-exact copy.
Usually 30 to 60 percent, and the spread depends on the material. Densely mixed loud music compresses worst; classical recordings and speech with pauses compress best. Silence and steady passages compress heavily, so voice recordings often lose more than half their size.
Only file size and encoding time, never the sound: at every level the decoded result is bit-identical to the original. The gap between level 5 and level 8 is typically one to three percent of size while taking several times longer, which is why 5 is the default.
The sample rate always survives: the tool parses the WAV header itself instead of pushing audio through the browser audio engine, which would turn 44.1 kHz into 48 kHz. Bit depth survives for integer files at 8, 16 and 24 bits. It cannot survive for 32-bit float, because FLAC only stores integers: such a file is written as 24 bits with an explicit note in the status line and a count of the clipped samples.
Exotic WAV variants — ADPCM, A-law, μ-law and other compressed flavours of the container. For those the tool falls back to the browser decoder and states plainly in the status line that the result is not bit-exact. Ordinary PCM files from editors and recorders are handled directly.
No. The libFLAC library is loaded onto the page as an ordinary script and runs inside your browser, while the audio is read from your own filesystem. No network request carries the file contents, as the Network tab of developer tools will confirm.
Before: session.wav, 44100 Hz, 16-bit stereo, 52 MB
After: session.flac at roughly 30 MB — audio identical to the source
Before: master.wav, 48000 Hz, 24-bit
After: master.flac — 48000 Hz and 24 bits preserved, no resampling
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