MKV to M4B Converter

How to Convert MKV to M4B Online

1. Upload Your MKV File: Drag and drop or click "Add Files" to select one or more MKV videos. Batch is supported, so a whole lecture series or audiobook split across multiple MKVs converts in one pass.
2. Pick a Quality Preset: Default is Highest. For single-narrator audiobooks, Medium (around 96 kbps AAC) or High (around 128 kbps AAC) is plenty — speech compresses far more efficiently than music. Drop to Low or Very Low if you want a tiny file for phone storage. Power users can switch to Custom Bitrate or Constant Bitrate to dial in an exact value.
3. Tune Audio Channel and Sample Rate (Optional): Set Audio Channel to Mono for a single narrator (halves the file size with no audible loss), Stereo for dramatized productions, or Original to keep the source layout. Audio Sample Rate accepts Original, 8000, 12000, 16000, 24000, 44100, or 48000 Hz — 22-24 kHz is fine for plain speech, 44.1 kHz is the safe default for anything with music or sound effects.
4. Trim and Convert: Use Trim with start time and duration in seconds or HH:MM:SS.sss to extract a single chapter or clip out intros and outros. Click Convert. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark, never shared.

Why Convert MKV to M4B?

MKV (Matroska) is a flexible video container that often holds audiobook recordings, recorded lectures, or video podcasts. M4B is the audiobook variant of MPEG-4 Part 14 — same container as MP4 and M4A, same AAC audio codec, but the .m4b extension tells players this is long-form spoken word, so they enable resume-on-reopen and chapter navigation. Converting MKV to M4B strips the unused video track and produces a file that Apple Books, Audiobookshelf, Smart Audiobook Player, and Plex treat as an audiobook rather than a music track.

• Apple Books and iTunes/Music import — Drag an M4B into the Music app on macOS or sync via Finder/iTunes and the file lands in the Audiobooks library, not the Songs library, with playback position preserved across sessions.
• Audiobookshelf and Plex audiobook libraries — Self-hosted audiobook servers scan .m4b files specifically and expose chapter markers in the player UI; an MKV with a video track does not get picked up.
• Long lectures and language courses — A 4-hour MKV lecture recorded in OBS or Zoom drops from roughly 1-2 GB to under 200 MB once the video track is gone and audio is re-encoded at 64-96 kbps mono AAC.
• Video podcast archival — Many podcasts ship MKV/MP4 video for YouTube and need an audio-only artifact for offline listening with bookmark support.
• Phone and Apple Watch storage — At 64 kbps AAC mono, one hour of speech is roughly 28 MB, so a 30-hour novel fits in under 900 MB on the device.
• Accessibility workflows — Screen-reader and audiobook apps surface M4B files in dedicated audiobook UIs that don't shuffle, repeat, or autoplay the next track.

MKV vs M4B — Format Comparison

M4B vs M4A vs MP3 — When to Pick Which

Recommended Bitrate by Content Type

Frequently Asked Questions

What is M4B and how is it different from MP4 or M4A?

M4B, M4A, and MP4 all use the MPEG-4 Part 14 container and (typically) AAC audio. The extension is the difference: .mp4 signals video, .m4a signals music, .m4b signals audiobook. Apple Books and most audiobook apps key off the .m4b extension to enable resume-from-position and chapter navigation. Renaming an .m4a to .m4b works for the resume feature in some players but won't add chapter markers if the file doesn't already have them embedded.

Will Apple Books recognize the M4B I create here?

Yes — drop the converted M4B into the Music app on macOS (or sync via Finder on a Mac, or iTunes on Windows) and it appears in the Audiobooks library with playback position preserved. If you don't see the file in the Audiobooks list, right-click in iTunes/Music and choose "Get Info → Options → Media Kind: Audiobook" to force the categorization.

Why is Mono recommended for audiobooks?

A single narrator records on one mic, so both stereo channels carry essentially the same signal — switching to Mono halves the file size with zero audible loss. Stereo is only worth the bytes for dramatized productions with multiple voice actors, environmental sound design, or music beds where left/right placement matters.

What bitrate should I pick for spoken-word content?

64 kbps AAC mono is the sweet spot for plain narration — speech occupies roughly 300 Hz to 8 kHz and AAC at 64 kbps preserves that range cleanly. Bump to 96-128 kbps if the recording has music or layered effects, or if the source MKV's audio is already high quality and you want to preserve headroom for further editing.

Can I extract just one chapter from a long MKV?

Yes. Use the Trim controls to set a start time and duration. Times accept either total seconds (5400 for 1 hour 30 minutes) or HH:MM:SS.sss format (01:30:00.000). For multiple chapters as separate M4B files, run the conversion once per range — each output is independent.

Does this preserve chapter markers from the MKV?

MKV-embedded chapter markers do not always survive a re-encode to M4B in browser-based converters; if your source MKV has chapters and you need them carried into the M4B, the most reliable workflow is to convert audio first and then add chapters with a desktop tool such as mp4chaps (part of mp4v2) or AudioBookConverter, which read and write M4B chapter atoms directly.

Will the M4B play on Android and Windows?

Yes, with a dedicated audiobook app. On Android, Smart Audiobook Player, Listen Audiobook Player, Voice, and VLC all play M4B and respect bookmark/chapter metadata. On Windows, VLC and foobar2000 play M4B; the default Music/Movies & TV apps may not surface .m4b files, so you may need to point them at the file explicitly or rename the extension to .m4a (which loses the audiobook treatment).

What happens to the video track during conversion?

It's discarded. M4B is audio-only by spec — the converter decodes the MKV's selected audio stream, re-encodes it to AAC at the bitrate and sample rate you picked, and wraps it in an MPEG-4 audio container with the .m4b extension. If you need the video too, convert to MKV to MP4 instead.

My MKV has multiple audio tracks (commentary, dub, original). Which one gets used?

The default audio track in the MKV is selected. If your MKV has, say, an English original and a Spanish dub and the wrong one is being used, remux the MKV with mkvtoolnix to set the desired track as default before uploading, or convert to MKV to MP3 / MKV to M4A first if you need a quick audio-only artifact while you sort out the track ordering.