M4B to FLAC
Nothing you choose here leaves your browser. There is no server to send it to — the conversion happens on your own device, and nothing is uploaded, stored or seen by anyone.
What this conversion costs you
An audiobook, losslessly, from here on. An .m4b is an M4A with an extension that tells a player to remember your place. FLAC keeps exactly what the M4B decodes to, which is already missing what AAC discarded. It will also be several times larger than the audiobook you started with, for no audible gain.
Your sample rate, kept
This is the part other browser-based converters get wrong without telling you. The web audio decoder resamples everything to your device's own rate — usually 48,000 Hz — so a 44,100 Hz file, which is every CD rip and most MP3s, comes back with its 44,100 samples a second interpolated into 48,000. The audio is subtly changed and nothing says so.
This page reads the sample rate out of the file's own header first, then decodes at that rate, so the samples are the ones you started with. The table above says which rate it found and confirms it was kept. Where a file's header cannot be read, it says that instead of pretending.
How it works, and why nothing is uploaded
Your browser decodes the M4B itself, using the codec your operating system already has. No browser WRITES FLAC, so this page offers to fetch an encoder: served from this site, fetched only if you ask and only once, and kept in your browser's ordinary cache. Nothing is installed and your recording is never sent anywhere.
Where to go next
- M4B to MP3 — the format everything has played for thirty years
- M4B to WAV — uncompressed, enormous, and readable by anything
- M4B to OGG — Vorbis, smaller than MP3 at the same quality
What this does not do
It converts whole files and does not trim, join, change the volume or alter the tags — the artist and title in your original do not survive, because the audio is decoded to raw samples and encoded again. It does not write AAC or M4A: those patents have not expired, and this site will not open that question for a format people already have.
Nothing is uploaded, so it cannot work on a file that is not on the device you are using, and a long recording will use a lot of memory while it is being converted.