AudiobookBuilder

Build chaptered .m4b audiobooks for Apple Books from folders of audio files.

AudiobookBuilder turns naturally ordered MP3, M4A, WAV, or FLAC tracks into one Apple Books-ready audiobook. It encodes AAC audio, writes a chapter for every source file, embeds useful metadata and optional cover art, and supports whole-series batch jobs.

Why it exists

A folder of narration tracks is not quite an audiobook. Apple Books expects an MPEG-4 audiobook container, consistent AAC audio, useful metadata, and chapter boundaries. AudiobookBuilder handles that assembly in one command without hiding the FFmpeg pipeline behind a fragile desktop wrapper.

Highlights

• One chapter per source file, ordered with natural filename sorting
• AAC .m4b output optimized for Apple Books with faststart
• Title, author, album, genre, and optional JPEG/PNG cover art
• Exact duplicate detection before encoding
• Flat-folder and one-book-per-subfolder batch workflows
• Parallel batch encoding with safe temporary outputs
• Native Apple AudioToolbox AAC selection when FFmpeg provides it
• Dry runs and explicit overwrite controls

Install

AudiobookBuilder supports macOS and Python 3.9 or newer.

brew install ffmpeg pipx
pipx ensurepath
pipx install audiobook-builder

Open a new terminal after pipx ensurepath, then confirm both tools are available:

audiobook-build --version
ffmpeg -version

To install the latest source directly from GitHub:

pipx install git+https://github.com/AhHamedi/AudiobookBuilder.git

Quick start

Given a folder like this:

The Long Way Home/
├── 01 Opening.mp3
├── 02 The Journey.mp3
└── 03 Homecoming.mp3

Run:

audiobook-build build "The Long Way Home" \
  --title "The Long Way Home" \
  --author "A. Narrator"

The default output is The Long Way Home/The_Long_Way_Home.m4b. Add it to Books by double-clicking the file or choosing File → Add to Library.

Add cover art or choose another destination when needed:

audiobook-build build "The Long Way Home" \
  --title "The Long Way Home" \
  --author "A. Narrator" \
  --cover cover.jpg \
  --out ~/Audiobooks/the-long-way-home.m4b

Batch builds

One subfolder per audiobook

Library/
├── Book One/
│   ├── 01 Intro.mp3
│   └── 02 Chapter.mp3
└── Book Two/
    ├── 01 Intro.flac
    └── 02 Chapter.flac

audiobook-build batch Library \
  --one-subfolder-per-book \
  --author "A. Narrator"

Numbered groups in one flat folder

Files beginning with the same number become one audiobook. This is useful when a series was exported into a single directory:

01 Earthsea Book 1 01.mp3
01 Earthsea Book 1 02.mp3
02 Earthsea Book 2 01.mp3
02 Earthsea Book 2 02.mp3

audiobook-build batch Series --author "A. Narrator"

Batch output defaults to the parent of the input directory. Use --out-dir, --jobs, --skip-existing, or --force to control larger runs. Run with --dry-run first to inspect the grouping and output names without encoding.

Command reference

audiobook-build build DIRECTORY --author TEXT [OPTIONS]
  --title, -t TEXT       Audiobook title; inferred from the first filename
  --out, -o PATH         Output file; .m4b is added automatically
  --bitrate TEXT         AAC bitrate (default: 96k)
  --encoder TEXT         auto, aac, or aac_at (default: auto)
  --cover, -c FILE       JPEG or PNG artwork
  --dry-run              Inspect tracks without encoding
  --force, -f            Overwrite an existing output

audiobook-build batch ROOT --author TEXT [OPTIONS]
  --out-dir, -o PATH     Output directory; defaults to ROOT's parent
  --one-subfolder-per-book
                          Treat each immediate child directory as one book
  --title-template TEXT  Use {n} for the detected group or folder name
  --jobs, -j INTEGER     Parallel encodes; 0 selects automatically
  --skip-existing        Keep outputs that already exist
  --force, -f            Overwrite without prompting
  --cover FILE           Apply one cover to every output
  --dry-run              Show the batch plan without encoding

Run audiobook-build COMMAND --help for the authoritative option list.

Verify an output

Inspect the container metadata and chapter boundaries with FFprobe:

ffprobe -v error \
  -show_entries format_tags=title,artist,genre:chapter=start_time,end_time:chapter_tags=title \
  -of json "The_Long_Way_Home.m4b"

A successful file reports AAC audio, the requested metadata, and one contiguous chapter per source track.

How it works

1. Discover supported files in the selected folder and sort their names naturally.
2. Remove byte-for-byte duplicates while preserving the first occurrence.
3. Read each duration with FFprobe and generate FFMETADATA chapter boundaries.
4. Concatenate and encode the tracks to AAC in a temporary .m4b.
5. Attach optional cover art and atomically move the completed file into place.

All media processing is performed locally. AudiobookBuilder does not upload audio or contact an external service.

Troubleshooting

ffmpeg and ffprobe were not found
Install FFmpeg with brew install ffmpeg. If you keep custom binaries elsewhere, point AudiobookBuilder to their directory:

export AUDIOBOOK_FFMPEG_DIR="/path/to/ffmpeg/bin"

The directory must contain executable files named ffmpeg and ffprobe.

The output title is not what I expected
Pass --title for a single book or --title-template 'Series {n}' for a batch.

Books shows no cover
Use a JPEG or PNG file with --cover. Square artwork around 1400–3000 px is the most reliable choice.

Encoding is using too much CPU
For a batch, reduce concurrency with --jobs 1 or another explicit value.

Limitations

• macOS and Apple Books are the supported v1 target.
• Input discovery is intentionally limited to immediate MP3, M4A, WAV, and FLAC files.
• MP4/MOV video extraction, DRM-protected media, tag-based track ordering, and cue sheets are not supported.
• Audio is re-encoded to AAC for consistent .m4b compatibility; this is not a lossless remuxer.

Development

python3 -m venv .venv
source .venv/bin/activate
python -m pip install -e '.[dev]'
ruff check .
ruff format --check .
pytest

See CONTRIBUTING.md for the complete contributor workflow and CHANGELOG.md for release history.

License

AudiobookBuilder is available under the MIT License.