m4b-tool

build, split, and tag M4B audiobooks from MP3 or other audio sources

TLDR

Merge a folder of MP3s into an M4B with chapters

$ m4b-tool merge [folder/] --output-file=[audiobook.m4b]

Split an audiobook by chapters into separate files

$ m4b-tool split --audio-format=mp3 [audiobook.m4b]

Refresh embedded chapter markers

$ m4b-tool chapters --adjust-by-silence [audiobook.m4b]

Merge with full metadata

$ m4b-tool merge [folder/] --output-file=[book.m4b] --name="[Title]" --artist="[Author]" --album="[Series]"

Convert a single MP3 to M4B

$ m4b-tool merge [file.mp3] --output-file=[file.m4b]

Add a cover image to an existing file

$ m4b-tool meta --cover=[cover.jpg] [audiobook.m4b]

SYNOPSIS

m4b-tool command [options] [input]

m4b-tool is a PHP-based command-line wrapper around ffmpeg and mp4v2 that creates, splits, retags, and inspects M4B audiobook files. The merge subcommand concatenates a directory of audio files (MP3, M4A, WAV, FLAC, etc.) into a single AAC-encoded M4B, automatically inserting chapter markers based on the order of input files or an accompanying chapters.txt.The split subcommand reverses the process, exporting each chapter as a separate file in a chosen format. chapters allows inspecting or rewriting the chapter table, optionally aligning markers to detected silences with --adjust-by-silence for better playback experience. meta edits ID3/MP4 tags and can embed cover artwork.A persistent cache speeds up repeated runs across the same files; disable it with --no-cache when input changes are not being detected.

PARAMETERS

merge

Combine multiple input files into one M4B with chapters preserved.

split

Split an M4B by chapter into one file per chapter.

chapters

Inspect, generate, or rewrite chapter markers (supports --adjust-by-silence).

meta

Read or update tags such as title, artist, cover art, and description.

--output-file FILE

Path to the output file (M4B).

--audio-format FORMAT

Output audio format for split (m4b, m4a, mp3, ...).

--name TITLE

Book or album title.

--artist NAME

Author or narrator name.

--album TEXT

Album/series name.

--cover FILE

Embed a cover image (JPEG or PNG).

--jobs N

Number of parallel encoding jobs.

--no-cache

Disable caching of intermediate analysis results.

CAVEATS

Requires ffmpeg and mp4v2 binaries on PATH plus a working PHP 7.4+ runtime. Encoding quality is governed by ffmpeg flags; high-bitrate libfdk_aac builds give the best results. Long audiobooks can take significant CPU and disk space for the merge stage.

HISTORY

m4b-tool was written by Andreas Sandberg (sandreas) and is distributed under the MIT license. It became popular as an open-source alternative to commercial M4B builders, particularly for Linux users who maintain audiobook libraries with Audiobookshelf or Plex.