Can this convert a whole audiobook?

Usually not. The limit is 30 minutes and 100 MB per file, because your browser holds all the decoded audio in memory: 8 hours of stereo would take about 9.5 GB. A longer file is turned away before decoding starts. For a whole book, use a desktop program such as FFmpeg.

Are chapters and cover art kept?

No. The MP3 is one continuous audio file with no chapter markers, cover art or tags. You can add a title, author and cover afterwards with the MP3 Tag Editor, but not the chapters. If you rely on chapters, keep the M4B.

Why won't my Audible or Apple Books file convert?

Because it is copy protected. This page works only on files without DRM, and does not help with removing protection. Audible's .aax and .aaxc files are refused by their ending; a protected .m4b is recognized from its header and named as protected.

Does converting M4B to MP3 lose quality?

A little. The AAC audio is decoded and compressed again as MP3, and both are lossy. For a spoken book at 96 or 128 kbps it is rarely something you would notice, but keep the M4B, since the MP3 cannot give back what was lost.

No. Reading, decoding and writing the MP3 all happen in your browser, so the audio stays on your device. The page counts ordinary analytics events, such as a conversion finishing and the bitrate used, but never the file or its name.

M4B to MP3 Converter

A free M4B to MP3 converter for short audiobook files without DRM: a single chapter, a sample, a talk or a podcast episode saved as .m4b. Your browser decodes the file and writes the MP3 on your device, so nothing is uploaded.

Limit: 30 minutes and 100 MB per file. Most whole audiobooks run for hours and will be turned away, with a clear message, before any decoding starts.

Drop your M4B here or click to browse

M4B without DRM, up to 100 MB and 30 minutes. M4A, AAC, MP4 audio and other common audio files work too.

The file stays on this device. Convert only audio you have the right to copy.

How to convert M4B to MP3

One file at a time. The page reads the length from the file's header first, so a file that is too long stops right away.

1
Drop the M4B
Drag the .m4b onto the converter or tap to pick it. A file over 30 minutes or 100 MB gets a message saying so, and a copy-protected file is named as one.
2
Pick a bitrate
128 kbps is preselected, and the converter offers 96, 128, 192 and 320. For one voice reading, 96 is usually enough and saves a quarter of the size.
3
Convert and save
Your browser decodes the AAC audio and an MP3 encoder inside the page writes the new file. Listen to the preview, then save the MP3 under the same name.

Your file ends in .m4a? Use the M4A to MP3 Converter. To give the finished MP3 a title, author and cover, use the MP3 Tag Editor.

What fits, and why a whole audiobook usually does not

The browser unpacks the entire file into memory before the MP3 is written. A compressed audiobook looks small on disk, but unpacked audio takes four bytes per sample, per channel. That is where the 30-minute limit comes from.

Length	M4B at 64 kbps	Decoded in memory	This page takes it
10 minutes	4.6 MB	201.9 MB	Yes
30 minutes	13.7 MB	605.6 MB	Yes
1 hour	27.5 MB	1.2 GB	No, over 30 minutes
3 hours	82.4 MB	3.5 GB	No, over 30 minutes
8 hours	219.7 MB	9.5 GB	No, over 30 minutes and 100 MB

Bitrate × seconds ÷ 8 for the file; 44,100 samples a second × 4 bytes × 2 channels for memory (mono takes half). 64 kbps is an example; your file may differ. 1 MB = 1,048,576 bytes.

What M4B is

M4B is the same MP4 container as M4A. The ending signals an audiobook or podcast, and those files can hold chapter markers and images. The sound inside is usually AAC, so to your browser's decoder an M4B and an M4A are the same kind of file; it goes by the bytes, not the ending or the file type your system reports.

For a whole book, a desktop program such as the free FFmpeg suits the job better, because it works through a file piece by piece and does not hold all of it in memory. That is also the honest answer if your file is too long here.

M4B next to the formats around it

File	Audio inside	Chapters and cover	Copy protection	On this page
M4B	Usually AAC	Can hold them	Often, on store purchases	Yes, without DRM
M4A	AAC, sometimes Apple Lossless	Can hold them	Usually none	Yes
M4P	AAC	Not the point of the format	Yes, FairPlay	No
AAX, AAXC	Audible's own formats	Audible app features	Yes	No
MP3 from this page	MP3	None	None	The result

What the MP3 keeps and what it loses

It keeps the sound, as one continuous file. It does not keep chapter markers, cover art, or the title and author tags: the page writes MP3 audio frames and nothing else, and your player's bookmarks live outside the file anyway. If you need chapters, keep the M4B.

There is a small quality cost too. AAC and MP3 are both lossy, and MDN warns that lossy compression is compounded by recompressing. What the M4B already dropped does not come back, and a little more goes at this step, so keep the original file.

Only files without DRM

This page cannot convert copy-protected audiobooks, and it will not show you how to get around protection. Audible's AAX and AAXC downloads and protected files from Apple Books will not work. DRM-free M4B files do: those you made yourself, or ones the seller provides without protection.

Which bitrate to pick

These are rules of thumb, not standards, and the choice stays yours.

One voice: 96 kbps
Speech has less detail to keep than a full band, and the file stays small. MDN describes AAC as built for more compression than MP3, so do not match a 64 kbps M4B with a lower MP3 number; 96 is the lowest here.
Voice with music beds: 128 kbps
The default. A book with music between chapters needs the extra room more than a plain reading does.
Music: 192 kbps
A sensible start for music. 320 makes the file two thirds bigger again, and cannot add anything the M4B no longer holds.

Recording your own talks and meetings?

An audiobook is for listening. For your own meetings and lectures, ParrotNotes records them on your phone, transcribes them and summarizes them, so you can read back what was said.

Get Started Free

Related tools

M4B to MP3 FAQ

Sources

M4B to MP3 Converter

How to convert M4B to MP3

Drop the M4B

Pick a bitrate

Convert and save