MP4 to M4B Converter

Convert MP4 to M4B — Turn a Recording into a Resumable Audiobook

M4B is the MPEG-4 audiobook format: the same AAC audio and MP4 container as an ordinary video, but with a .m4b extension that tells audiobook apps to treat the file as a book. This converter pulls the audio out of an MP4 (or .m4v) and saves it as M4B, so a recorded lecture, sermon, conference talk, or narrated video plays like an audiobook — you stop, close the app, and it picks up exactly where you left off. There is no video in the result; it is an audio-only extraction, re-encoded to AAC.

M4B Format at a Glance

Why Turn a Lecture, Sermon, or Long Recording into an M4B

A raw MP4 keeps the full video stream, so it is many times larger than the audio alone, and most audiobook apps will not import a video file as a book at all. Extracting to M4B drops the picture entirely and leaves a compact AAC audio file that audiobook players accept — and, crucially, resume. For anything you listen to in long sittings, that resume bookmark is the whole point:

• Lectures and lessons — a two-hour recorded class becomes a file you can start on a commute and resume the next day without scrubbing to find your place.
• Sermons and talks — a Sunday service or conference session plays back in an audiobook app that keeps your position across days, not just within one sitting.
• Narration and personal recordings — a self-recorded reading or a long voice memo becomes a proper, resumable audiobook instead of a video file gathering dust.

If you would rather have a plain music track or maximum device compatibility, extract to M4A or MP3 instead — the trade-off is that neither remembers your place the way an M4B does.

M4B vs M4A vs MP3 for Audiobooks

M4B and M4A are technically the same MPEG-4 + AAC file; the .m4b extension is the signal that makes players behave like an audiobook rather than a music track. Choose M4B when the resume bookmark matters, and MP3 only when you need a file that plays on essentially any device.

How to Convert MP4 to M4B

1. Upload Your MP4 File: Drag and drop your .mp4 or .m4v file, or click "Add Files" to browse. You can queue several recordings and convert them all with the same settings.
2. Set the Bitrate under File Compression: The output codec is AAC, the standard for M4B. Open Advanced Options — File Compression opens on Quality Preset, the automatic mode with nothing pre-selected in it, so switch it to Constant Bitrate (a dropdown running from 8 to 384 kbps and opening on 128 kbps), Custom Bitrate, or Variable Bitrate to control size — 64 kbps is the sweet spot for a single narrator.
3. Downmix or Trim (Optional): Set Audio Channel to Mono to roughly halve the size of a voice recording, leave Audio Sample Rate on Original, or use Trim to keep just one Time Range (start plus duration) instead of the whole file.
4. Convert and Download: Click Convert and download your .m4b. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark.

Frequently Asked Questions

Will the M4B remember where I stopped like a real audiobook?

Yes, in apps that honor the audiobook format. Apple Books and most dedicated audiobook players recognize a .m4b file as a book and automatically save your playback position, so reopening resumes exactly where you stopped instead of restarting. With .m4a or .mp3, most apps treat the file as music and begin again from the start. The position memory is created by the player once it sees the file is an audiobook — it is not something the converter writes into the audio itself.

Does this add chapter markers or split the recording into chapters?

No. This converter extracts and re-encodes the audio into a single, continuous M4B; it neither imports nor creates a chapter table, and it does not split the recording into per-chapter files. A plain video has no chapter data to carry over in the first place. If you only want one part of the recording, use the Trim controls to export a single Time Range instead of the whole file. Resume playback still works without chapters, because that comes from the file being recognized as an audiobook.

Why extract to M4B instead of just keeping the MP4 video?

Two reasons: size and behavior. An MP4 carries the entire video stream, so it is far larger than the audio alone, and most audiobook apps will not import a video file as a book. Extracting to M4B drops the video track completely, leaving a compact AAC file that audiobook players both accept and resume. For a recorded lecture or sermon you plan to listen to over several sittings, that is exactly the format you want.

What bitrate should I use for a lecture or sermon recording?

Spoken word needs far less bitrate than music. 64 kbps AAC is the audiobook sweet spot — clear voice at a small size, and it matches what many commercial audiobooks use. Step up to 96–128 kbps if the recording has music, background tone, or several voices you want to keep full. Going above the source bitrate cannot add quality back; it only makes the file bigger. Setting Audio Channel to Mono on a single-voice recording roughly halves the size again with no audible loss.

Can I convert a DRM-protected video or Audible file to M4B?

No. Files locked with Apple's FairPlay DRM (for example, videos or audiobooks bought from the Apple stores) and Audible's AAX files are encrypted, so a converter sees scrambled data and cannot re-encode them. This is true of every online converter, not just ours. Personal recordings, self-made videos, and public-domain material are DRM-free and convert without issue; protected purchases are blocked by design and have to be handled through the rights holder's own authorized method.

Will Apple Books show my converted file as an audiobook?

In most cases, yes. When you add a .m4b file to Apple Books it appears under Audiobooks rather than in your music library, and it remembers your position between sessions. On a computer you typically add the file through the Books app or Finder; on an iPhone or iPad you can open the downloaded .m4b and choose to save it to Books. If a file lands in the wrong library, it is almost always because the extension got changed to .m4a somewhere along the way — keep it as .m4b.

How big will a multi-hour recording be, and is there an upload limit?

There is no fixed per-file cap. At 64 kbps a recording runs roughly 28–29 MB per hour, so a multi-hour lecture set is routine — the real limit is upload size and your connection speed, since conversion happens on our servers rather than on your device. A large file simply takes longer to upload than a short clip. To shrink a finished M4B for email or a chat app, the Audio Compressor can target an exact output size.

What exactly does this converter output, and are my files kept private?

In our testing, a 60-minute lecture MP4 exported at 64 kbps AAC produced an M4B of about 29 MB — AAC audio inside an MPEG-4 container with the .m4b extension that Apple Books treats as a resumable audiobook. The audio is re-encoded, so a Constant Bitrate at or above the source keeps the result indistinguishable from the original for speech — that is the control to name explicitly, since the Quality Preset dropdown is the automatic mode with nothing pre-selected in it and is the least predictable option on the page. The conversion does not inject chapters or cover art that were not already there. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion — never shared, never made public, and no sign-up required.