Cut and trim M4B audiobook files online. Extract chapters and segments with compression, channel, and sample rate control.
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.m4b audiobook. Multiple files can be queued and trimmed in sequence.HH:MM:SS (or seconds). Use a chapter timestamp from your audiobook player as the start, and set the duration to the chapter length to extract a single chapter..aax files must be unlocked by the rights holder first).M4B is Apple's audiobook container — AAC audio inside an MPEG-4 wrapper, with chapter markers and a bookmark flag that tells players to remember playback position. Audiobooks routinely run 8 to 40+ hours, so a single .m4b is often 100 MB to 1 GB. Trimming lets you pull out the part you actually want.
.m4b at 64 kbps mono is about 345 MB. Trimming a 25-minute chapter drops that to roughly 12 MB — small enough to email or sync to a basic MP3 player.| Property | M4B | MP3 | M4A |
|---|---|---|---|
| Container | MPEG-4 | MPEG-1/2 Audio Layer III | MPEG-4 |
| Codec | AAC (typically AAC-LC) | MP3 | AAC |
| Chapter markers | Native, embedded | Not native (ID3 hacks only) | Native (rarely used) |
| Position bookmarking | Yes — apps treat .m4b as audiobook |
No | No (treated as music) |
| Apple Books support | Yes — auto-files into Audiobooks | Limited | No |
| Typical audiobook bitrate | 64 kbps mono AAC | 96-128 kbps mono | 64-128 kbps mono |
| File size, 10 hrs spoken word | ~290 MB at 64 kbps | ~430 MB at 96 kbps | ~290 MB at 64 kbps |
| Best for | Audiobooks with chapters | Maximum player compatibility | Music tracks |
| Setting | Bitrate (mono) | ~Size per hour | Best for |
|---|---|---|---|
| Lowest / 32 kbps | 32 kbps | ~14 MB | Lectures, podcasts, voice memos where size dominates |
| Low / 48 kbps | 48 kbps | ~22 MB | Long audiobooks on small devices |
| Medium / 64 kbps | 64 kbps | ~29 MB | Spoken-word sweet spot — recommended default |
| High / 96 kbps | 96 kbps | ~43 MB | Audiobooks with music beds or sound design |
| Very High / 128 kbps | 128 kbps | ~58 MB | Full-cast productions, dramatic readings |
| Highest / 160-192 kbps | 160-192 kbps | ~72-86 MB | Mastering, archival, source files for re-encoding |
| Scenario | Start Time | Duration | Notes |
|---|---|---|---|
| Extract a single chapter | Chapter start (from your player) | Chapter length | Note timestamps before trimming — chapter markers are not preserved across re-encode |
| Skip publisher intro | 60-90s | Total minus intro and outro | Removes legal/branding reads |
| 5-minute audition clip | Strong-passage start | 300s | For narrator auditions or marketing samples |
| Split for older iPods | Part start time | 1-2 hour blocks | Avoids file-system or 4 GB FAT32 caps |
| Recover from cutoff | 0s | Time just before corruption | Salvages playable portion |
No. Trimming re-encodes the audio segment, and the new file is a fresh AAC stream without the original chapter table. The output is still a valid .m4b (so Apple Books and audiobook players still treat it as an audiobook and bookmark your position), but the per-chapter jump points and titles from the source are lost. Note your chapter timestamps before you trim if you want to recreate them later, or trim each chapter into its own file.
The audio inside is identical — both are AAC in an MPEG-4 container. The .m4b extension and an audiobook flag in the file metadata tell players to auto-bookmark playback position and surface the file in audiobook libraries (like Apple Books) instead of music libraries. Renaming .m4a to .m4b works in many players but does not always trigger the bookmark behavior; encoding properly to M4B is more reliable.
Use "Quality Preset" (variable bitrate) for general audiobook trimming — VBR allocates more bits to complex passages and fewer to silence, producing slightly smaller files at the same perceived quality. Use "Constant Bitrate" when you need predictable file sizes (for example, fitting an exact 1-hour clip into a known megabyte budget) or when compatibility with very old hardware is a concern. For spoken word, the difference is small.
.aax / .aa)?No. Audible's .aax and .aa files are encrypted with FairPlay-style DRM that is bound to your Audible account. xconvert does not strip DRM. You'll get an error or a silent track if you upload one. Audible files must be unlocked by the rights holder (typically through the Audible apps or by burning to CD) before any web tool can process them.
64 kbps mono AAC is the recognised sweet spot for clean spoken word — that's roughly 29 MB per hour. 96 kbps is worth it if there's music or sound design between narration. Going above 128 kbps for narration-only content rarely produces audible improvement and just doubles the file size.
Apple Books only auto-imports .m4b files placed in the right location and with the audiobook flag intact. After trimming, drag the file into the Books app on macOS, or sync via Finder on iOS. If Books still treats it as music (placing it in the Music app), the metadata flag may not have carried through — re-encoding through xconvert with explicit "Audiobook" output usually fixes this.
xconvert processes large audiobooks but very large files (multi-GB) can stall on low-RAM devices because the browser holds the file in memory. If you're working with a 20+ hour audiobook, trim in 1-2 hour passes, or split first then trim each piece. For batch chapter extraction across a single source, queue multiple trim jobs with different start/duration values rather than uploading the file repeatedly.
Queue the same source file multiple times with different start times and durations — each becomes its own trimmed .m4b. For example, to extract chapters 1, 3, and 7, add the file three times and set the start/duration for each chapter independently. There's no built-in chapter-aware splitter, but the trim panel handles arbitrary in/out points.
Trim first, then run the output through M4B to MP3 to get an MP3 of the trimmed segment. If you want to keep working in the M4B world (with bookmarking) but compress further, see Compress M4B. To convert your source from another audiobook format, MP3 to M4B and M4A to M4B handle the inbound side.