Third-party software and attributions

ChapterForge incorporates or relies on the following third-party components. The Python libraries below are bundled inside the application, as is libmpv-2.dll (see below); FFmpeg is downloaded at runtime rather than shipped with ChapterForge.

FFmpeg (`ffmpeg.exe`, `ffprobe.exe`)

License: GNU LGPL 2.1+ or GPL 2.0+ (depending on build configuration)

ChapterForge uses the FFmpeg command-line tools to decode, concatenate, and re-encode audio files. FFmpeg is maintained by the FFmpeg project and is available at https://ffmpeg.org.

ChapterForge does not bundle or redistribute FFmpeg. If FFmpeg is not already on your system, ChapterForge offers to download an official Windows build on first run (and via Help > Download FFmpeg). Those binaries are obtained directly from the third-party builder and remain under their own license.

If you choose to redistribute ChapterForge together with FFmpeg binaries, you become a redistributor of FFmpeg and must comply with FFmpeg's license terms (GPL or LGPL, depending on the build), which generally require:

Providing the FFmpeg source code (or a written offer of the source)
Keeping the FFmpeg license notice intact
Preserving all copyright and license notices in the binaries

For detailed information about FFmpeg licensing, visit https://ffmpeg.org/legal.html.

libmpv (`bin/mpv/libmpv-2.dll`)

License: GNU LGPL 2.1+ or GPL 2.0+ (depending on build configuration)

ChapterForge's in-app player uses libmpv, the playback engine of the mpv media player, via the python-mpv Python binding, to decode and play audio with sample-accurate seeking. libmpv is maintained by the mpv project (https://mpv.io) and is built for Windows by the mpv-player-windows project (https://github.com/shinchiro/mpv-winbuild-cmake, distributed via https://sourceforge.net/projects/mpv-player-windows/).

Unlike FFmpeg, ChapterForge does bundle and redistribute libmpv-2.dll (under bin/mpv/). As a redistributor, ChapterForge complies with libmpv's license terms (GPL or LGPL, depending on the build) by:

Providing this notice and a written offer of the corresponding source code: the exact build redistributed with ChapterForge is mpv-dev-x86_64 from the mpv-player-windows project's release channel; its source is the public mpv project source (https://github.com/mpv-player/mpv) plus the mpv-winbuild-cmake build scripts linked above. Contact the address in this project's README to request a copy.
Keeping libmpv's and mpv's license notices intact and available at https://github.com/mpv-player/mpv/blob/master/Copyright and https://www.gnu.org/licenses/.
Preserving all copyright and license notices in the binary.

Mutagen

License: GNU GPL v2.0 or later

ID3v2 tags and chapter frames (CHAP/CTOC) are written using the Mutagen Python library, a pure-Python library for reading and writing audio metadata. Mutagen is maintained at https://mutagen.readthedocs.io.

ChapterForge uses Mutagen to:

Parse and write ID3v2 tags in MP3 files
Create and embed CHAP/CTOC chapter frame structures
Maintain podcast app compatibility (Overcast, Pocket Casts, AntennaPod, etc.)

wxPython (wxWidgets)

License: wxWindows Library Licence (compatible with LGPL)

The ChapterForge graphical interface is built with wxPython, a cross-platform Python binding for wxWidgets. wxPython is maintained at https://www.wxpython.org.

The wxWindows Library Licence permits both commercial and open-source use, with the requirement that you acknowledge wxWidgets and provide a copy of the license with your application.

Prismatoid (optional, Windows)

License: Unlicensed / proprietary (optional graceful degradation)

The optional prismatoid package provides enhanced screen-reader output on Windows for NVDA compatibility. When installed, ChapterForge integrates with Windows Automation/MSAA to announce chapter progress and status. If prismatoid is not installed, ChapterForge gracefully falls back to visible status text and standard accessible controls.

QUILL (accessibility patterns)

Attribution: BITS (Blind Information Technology Solutions)

The screen-reader announcement and accessibility layer in ChapterForge (chapterforge/a11y.py and chapterforge/notify.py) is adapted from the QUILL project's accessibility design. This includes:

The Prism/Prismatoid screen-reader bridge with graceful fallback
The announce() transcript API for screen-reader feedback
The announcement formatting grammar (format_announcement(), format_progress(), pluralize())
The in-app JSON notification log pattern for accessibility and debugging

QUILL is an accessible document editor developed by BITS. ChapterForge reuses these proven patterns to ensure full screen-reader compatibility and keyboard-first operation.

Build & packaging tools

The following tools are used to build and package ChapterForge but are not bundled with the application:

PyInstaller (GitHub Installers) - creates the self-contained Windows executable
Inno Setup - builds the Windows installer
Python 3.10+ - runtime and build environment

ChapterForge is an accessible audiobook builder for Windows. For more information, visit https://github.com/bits-acb/chapterforge.