Audio to M4B Converter

How to Convert Audio to M4B Online

1. Upload Your Audio File: Drag and drop or click "Add Files" to select source audio. XConvert accepts 19 audio extensions including MP3, AAC, OGG, WMA, Opus, AMR, AC3, FLAC, WAV, AIF, AIFF, AIFC, AU, VOC, M4A, M4B, WEBA, OGA, and DSS voice memos. Batch is supported.
2. Pick Quality Preset or Bitrate: Default codec is AAC (M4B's native codec). Use Quality Preset (Highest through Lowest) for a one-click choice, or open Constant Bitrate to pick a fixed value (32, 48, 64, 96, 128, 192, or 320 kbps), Custom Bitrate to type any kbps value, or Variable Bitrate for size-efficient narration. For target-size workflows pick Specific File Size or File Size Percentage.
3. Set Audio Channel, Sample Rate, and Trim (Optional): Audio Channel defaults to Original — switch to Mono to halve narration file size with no audible loss, or Stereo if your source is music. Audio Sample Rate defaults to Original; common audiobook values are 22050 Hz or 44100 Hz. To split a long recording, open Trim and enter Start Time + Duration in seconds or HH:MM:SS.sss.
4. Convert and Download: Click Convert. Files process in your browser session and download individually or as a ZIP — no sign-up, no watermark.

Why Convert Audio to M4B?

M4B is Apple's audiobook file extension, introduced alongside iTunes and the iPod in the early 2000s. It uses the same MPEG-4 Part 14 container and AAC codec as M4A, but the .m4b extension flags the file as an audiobook so Apple Books, iTunes, and audiobook-aware players save your playback position automatically and surface chapter navigation. Converting MP3, FLAC, WAV, or other audio to M4B is the standard way to:

• Get resume-playback in Apple Books and iTunes — M4B stores a playhead position so you can pause a 14-hour book and pick up exactly where you left off. MP3 has no defined bookmark mechanism, so most apps drop you back at file start when reopened.
• Consolidate a multi-file podcast or lecture series — Combine episodes into one M4B locally with a tool like AudioBookBinder, then convert/recompress here. One file is easier to manage than a folder of 80 MP3s.
• Cut narration file size by 60-80% from MP3 — A 10-hour audiobook at 64 kbps mono AAC in M4B is roughly 280 MB. The same content as 128 kbps stereo MP3 is ~700 MB. AAC is more efficient than MP3 at low bitrates where speech lives.
• Prepare voice memos and DSS recordings for audiobook-style playback — Olympus / Philips dictation devices output DSS, iPhone Voice Memos output M4A. Re-encoded as M4B, these get the bookmarking and chapter UI in Apple Books rather than living in the Music or Files app.
• Replace a lossless WAV/FLAC archive with a portable distribution copy — A FLAC narration master at 800 kbps becomes a 64 kbps M4B that's 12× smaller and plays on any iPhone, iPad, Mac, or Apple Silicon device without conversion.
• Produce input for audiobook-aware Android apps — Smart AudioBook Player, Voice Audiobook Player, and BookPlayer-style apps all key off the .m4b extension to enable chapter and bookmark UI not exposed for .m4a or .mp3.

M4B vs M4A vs MP3 — Format Comparison

The container and codec are functionally identical between M4B and M4A — the difference is the extension and the metadata flags it triggers in playback apps.

AAC Bitrate Quick Guide for Audiobooks

For pure narration, AAC at 64 kbps mono is widely treated as transparent — Audible's standard "Format 4" Enhanced is roughly equivalent. There's rarely a reason to go above 96 kbps for spoken word.

Frequently Asked Questions

What is the difference between M4B and M4A?

M4B and M4A use the same MPEG-4 Part 14 container and almost always the same AAC codec. The functional difference is convention: the .m4b extension tells Apple Books, iTunes, and similar apps to treat the file as an audiobook — saving the playhead position between sessions and exposing chapter navigation. M4A files behave like music tracks and reset to the start each time you open them. Renaming a music .m4a to .m4b works for some apps but is fragile; re-encoding to M4B is the reliable path.

Will my chapters survive the conversion?

Chapter markers in the source file are dropped when re-encoding through this tool — output is a single continuous M4B with no embedded chapters. To preserve or author chapters, build the M4B locally with a tool like AudioBookBinder (Mac), m4b-tool (cross-platform CLI), or AudioBo (Mac) which write Nero or QuickTime chapter atoms that Apple Books recognizes. This converter is best for one-file recordings and post-processing tasks like bitrate or sample-rate change.

Can Apple Books on Mac and iOS open the M4B file?

Yes. Apple Books reads .m4b natively. On Mac, drag the file into the Books app or use File → Add to Library; the file appears in the Audiobooks section with resume-playback enabled. On iOS, AirDrop the M4B from Mac or use the Files app's Share menu. Sync via iCloud or a wired Finder transfer mirrors the audiobook to all your Apple devices. Note: M4B files purchased from the iTunes/Apple Books store can be DRM-protected (Apple's FairPlay) — files you create from your own audio are unprotected and play freely.

What bitrate should I use for narration?

64 kbps mono AAC is the audiobook standard — it's effectively transparent for spoken word and produces ~28 MB per hour. If your source has music or sound effects, jump to 96-128 kbps stereo. 32 kbps mono is acceptable for very-low-fidelity content like phone interviews or class recordings. Going above 128 kbps for pure narration mostly wastes space.

Why convert MP3 to M4B instead of just renaming the file?

The MP3 codec lives in MPEG-1/2 Layer III, not the MPEG-4 container that M4B uses, so a renamed file isn't a real M4B and most apps will refuse it or fail mid-playback. M4B requires the audio to be inside an MPEG-4 (ISO base media) container with AAC, ALAC, or another supported codec. This converter performs the actual re-encoding from MP3 → AAC and re-packages into the MPEG-4 container with the .m4b extension. See also MP3 to M4B for the MP3-specific page.

Can I batch convert multiple audio files into one M4B?

This converter processes each input as a separate M4B output (one in, one out). To merge multiple files into a single chaptered audiobook, concatenate or merge them first with a desktop tool, then run the merged file through this converter for bitrate/format adjustment. For trimming a long single file into shorter pieces, use the Trim controls per-conversion or see Audio Cutter.

Does M4B work on Android, Windows, and Linux?

Yes — M4B is a standard MPEG-4/AAC file. Windows Media Player, VLC (Win/Mac/Linux), foobar2000, MPV, and most modern players will play the audio. The bookmark and chapter UI is opt-in by app: on Android, Smart AudioBook Player and Voice Audiobook Player recognize the .m4b extension; on iOS/macOS, Apple Books and BookPlayer do the same. Generic players will play the audio but may not save your position between sessions.

Will track titles, author, and cover art transfer?

Tags written in the source file's MPEG-4 metadata atoms (M4A, M4B inputs) generally transfer. ID3 tags from MP3 sources also map across, including title, artist, album, year, and embedded cover art. To set audiobook-specific fields like Author, Narrator, or Genre = Audiobook, edit the output in iTunes/Apple Books or Mp3tag (Windows) before importing into your library.

Can I trim a long recording into chapters during conversion?

You can trim a single segment per conversion run using the Trim controls — enter Start Time and Duration in seconds or HH:MM:SS.sss format, and the output covers only that range. To produce multiple chapter files, run the converter once per chapter with different trim ranges, then merge the outputs locally with a chapter-aware tool. For complex multi-chapter authoring, see also WAV to M4B or FLAC to M4B for source-specific guidance.