Licensing & Open-Source Acknowledgements
This page describes how Convertessa works with third-party open-source tools, what licenses govern those tools, and what that means for the image, audio, video, and document formats you can process with the app.
How Convertessa uses third-party tools
Convertessa is a native macOS application. It does not bundle, embed, or distribute any of the open-source tools listed below. Each tool is either:
- a standard macOS system component that Apple ships with every Mac, or
- a tool installed separately by you via Homebrew or the tool's own installer.
When you ask Convertessa to convert a file, the app locates the appropriate tool already on your Mac and invokes it as a separate process (a technique called "shell-out"). The tool runs, Convertessa collects the output, and the tool exits. No tool code runs inside Convertessa itself.
This architecture means:
- You are always in control of what is installed. Convertessa will tell you when a tool is needed and where to get it. It never installs anything without your knowledge.
- External tools run as separate programs. Convertessa is designed to interact with these command-line tools as separate programs rather than bundling or linking them — it passes arguments and files and reads exit codes, with no in-process linking. Based on this architecture, our understanding is that the licenses of those external tools (including any GPL or LGPL copyleft terms) apply to those tools themselves. This is not a legal determination, and Convertessa's own code is proprietary.
- Each tool's license and patent position applies only to that tool, not to Convertessa as a whole.
Third-party tools
FFmpeg
| Website | ffmpeg.org |
| License | FFmpeg itself is licensed under the GNU LGPL v2.1+; depending on build options and the libraries it is linked against, a given build may instead be GPL (v2+ or v3). The Homebrew formula may include GPL-licensed components. The evermeet.cx macOS build is effectively GPLv3 (compiled with --enable-gpl --enable-version3 --enable-libx264 --enable-libx265; verified at evermeet.cx/ffmpeg/). Convertessa neither modifies nor redistributes these builds. |
| How it is installed | Via Homebrew (brew install ffmpeg) or as a pre-built macOS binary downloaded from evermeet.cx |
| What Convertessa uses it for | Audio and video format conversion: encoding, decoding, mux/demux across a wide range of containers and codecs |
Convertessa uses FFmpeg for audio and video processing. FFmpeg is licensed under the GNU LGPL version 2.1 or later; some optional components are licensed under the GPL version 2 or later. FFmpeg is installed by the user and is not bundled with Convertessa.
evermeet.cx builds: When you first set up FFmpeg through Convertessa's guided setup, the app may offer to download a pre-built macOS FFmpeg binary from evermeet.cx. These builds are maintained independently by Helmut K. C. Tessarek and are not affiliated with the FFmpeg project. The evermeet.cx build is GPLv3 (compiled with --enable-gpl --enable-version3 --enable-libx264 --enable-libx265; verified at evermeet.cx/ffmpeg/). Convertessa does not modify or redistribute this binary.
libvips
| Website | libvips.org |
| License | GNU LGPL version 2.1 or later |
| How it is installed | Via Homebrew (brew install vips) |
| What Convertessa uses it for | Image format conversion: JPEG, PNG, WebP, TIFF, AVIF (read and write), HEIC (read via libheif; write via Apple's ImageIO framework in a separate engine layer), GIF, BMP, PSD (read only), SVG rasterization (read only), JPEG XL (read only), EXR, HDR, PPM; camera RAW formats decoded by the libraw library libvips links to (read only): Canon RAW (.cr3, .crw), Nikon RAW (.nrw), Sony RAW (.sr2, .srf), Pentax RAW (.pef), Leica RAW (.rwl), Kodak RAW (.dcr, .kdc), Hasselblad RAW (.3fr, .fff), Phase One RAW (.iiq), Minolta RAW (.mrw), Mamiya RAW (.mef); additional raster formats decoded by the ImageMagick library libvips links to (read only): Windows Cursor (.cur), SGI RGB Image (.rgb, .rgba, .sgi, .bw), X BitMap (.xbm), GIMP XCF Image (.xcf) |
Convertessa uses libvips for image processing. libvips is licensed under the GNU LGPL version 2.1 or later. libvips is installed by the user and is not bundled with Convertessa.
ImageMagick (linked by libvips)
| Website | imagemagick.org |
| License | ImageMagick License (permissive; SPDX: ImageMagick; modeled on Apache-2.0; commercial use permitted). Verified at imagemagick.org/script/license.php. |
| How it is installed | Installed as a runtime dependency of libvips via Homebrew (brew install vips); linked by libvips internally — not invoked directly by Convertessa |
| What Convertessa uses it for | Decoding additional raster image formats via libvips (read only): Windows Cursor (.cur), SGI RGB Image (.rgb, .rgba, .sgi, .bw), X BitMap (.xbm), GIMP XCF Image (.xcf) |
libvips links to ImageMagick to decode certain raster image formats. The ImageMagick License is permissive and permits commercial use. Convertessa credits ImageMagick Studio LLC. ImageMagick is installed as a dependency of libvips and is not bundled with Convertessa.
libraw (linked by libvips)
| Website | libraw.org |
| License | Dual-licensed: GNU LGPL version 2.1 or CDDL version 1.0 (users may choose either). Verified at libraw.org/about. |
| How it is installed | Installed as a runtime dependency of libvips via Homebrew (brew install vips); linked by libvips internally — not invoked directly by Convertessa |
| What Convertessa uses it for | Decoding camera RAW formats via libvips (read only): Canon RAW (.cr3, .crw), Nikon RAW (.nrw), Sony RAW (.sr2, .srf), Pentax RAW (.pef), Leica RAW (.rwl), Kodak RAW (.dcr, .kdc), Hasselblad RAW (.3fr, .fff), Phase One RAW (.iiq), Minolta RAW (.mrw), Mamiya RAW (.mef) |
libvips links to libraw to decode camera RAW formats from a wide range of camera manufacturers. libraw is dual-licensed under the GNU LGPL version 2.1 and CDDL version 1.0; users may choose either license. libraw is installed as a dependency of libvips and is not bundled with Convertessa.
OpenSlide (linked by libvips)
| Website | openslide.org |
| License | GNU LGPL version 2.1 (not any later version). Verified at openslide.org/license/. |
| How it is installed | Installed as a runtime dependency of libvips via Homebrew (brew install vips); linked by libvips internally — not invoked directly by Convertessa |
| What Convertessa uses it for | Supports whole-slide image formats via libvips; no whole-slide conversion is currently advertised in Convertessa |
libvips links to OpenSlide, which supports whole-slide image formats. OpenSlide is licensed under the GNU LGPL version 2.1 (not any later version). OpenSlide is installed as a dependency of libvips and is not bundled with Convertessa.
pandoc
| Website | pandoc.org |
| License | GNU GPL version 2.0 or later |
| How it is installed | Via Homebrew (brew install pandoc) or via the pandoc.org installer |
| What Convertessa uses it for | Markup and document conversion: Markdown, AsciiDoc, reStructuredText, DocBook, MediaWiki, Org, Textile, OPML, Texinfo, man pages, LaTeX, JATS, Jupyter notebooks, ICML, Typst, Muse, Djot |
Convertessa uses pandoc for document and markup format conversion. pandoc is licensed under the GNU GPL version 2.0 or later. pandoc is installed by the user and is not bundled with Convertessa.
LibreOffice
| Website | libreoffice.org |
| License | Mozilla Public License 2.0 / GNU LGPL version 3 or later (mixed codebase) |
| How it is installed | Via Homebrew Cask (brew install --cask libreoffice) or via the libreoffice.org installer |
| What Convertessa uses it for | Office document conversion: DOCX, XLSX, PPTX, ODT, ODS, ODP, PDF, XLS, PPT, DIF, SYLK, and flat ODF formats |
Convertessa uses LibreOffice for office document conversion. LibreOffice is distributed under the Mozilla Public License 2.0 and the GNU LGPL version 3 or later. LibreOffice is installed by the user and is not bundled with Convertessa.
Calibre
| Website | calibre-ebook.com |
| License | GNU GPL version 3 |
| How it is installed | Via Homebrew Cask (brew install --cask calibre) |
| What Convertessa uses it for | E-book format conversion: EPUB, MOBI, AZW3, FB2 → PDF, DOCX, TXT |
Convertessa uses Calibre for e-book format conversion. Calibre is licensed under the GNU GPL version 3. Calibre is installed by the user and is not bundled with Convertessa.
DRM policy: Convertessa does not circumvent any DRM (digital rights management) protection. If a book is DRM-protected, Calibre will detect this and report it; Convertessa surfaces that error message and stops. Convertessa has no ability to remove or bypass DRM.
fontTools
| Website | github.com/fonttools/fonttools |
| License | MIT License. Verified at the project's LICENSE file and its PyPI project page. |
| How it is installed | Via Homebrew (brew install fonttools) |
| What Convertessa uses it for | Font format conversion: TTF (.ttf), OTF (.otf), WOFF (.woff), WOFF2 (.woff2), TTX (.ttx); reading TTC (.ttc, read only); glyph subsetting and variable-font instancing |
Convertessa uses fontTools for font format conversion, glyph subsetting, and variable-font instancing. fontTools is licensed under the MIT License. fontTools is installed by the user and is not bundled with Convertessa.
bsdtar (macOS system component)
| Website | libarchive.org |
| License | BSD 2-Clause License |
| How it is installed | Ships with macOS as /usr/bin/tar — not installed or distributed by Convertessa |
| What Convertessa uses it for | Archive creation and extraction: ZIP, TAR, TAR.GZ, TAR.BZ2, TAR.XZ, 7Z, RAR (read-only), ISO (read-only), and compressed streams (gz, bz2, xz) |
Convertessa uses bsdtar, a macOS system component based on libarchive, for archive handling. bsdtar is licensed under the BSD 2-Clause License. bsdtar is part of macOS and is not installed or bundled by Convertessa.
Sparkle (software updates)
| Website | sparkle-project.org |
| License | MIT License (with some bundled components under other permissive licenses) |
| How it is included | Linked into the Convertessa app (Sparkle 2.x) to deliver prompted, user-approved updates |
| What Convertessa uses it for | Checking updates.convertessa.app for new versions and installing updates you approve |
Convertessa uses the Sparkle framework for software updates. Sparkle is licensed under the MIT License. © Sparkle Project contributors.
Codecs and patents
Some media formats and codecs may be covered by patents or other rights in some jurisdictions. Convertessa does not grant any patent license. You are responsible for ensuring that your use of a particular format or codec is lawful in your jurisdiction and for your use case.
The third-party tools and codecs Convertessa relies on may have their own terms, which apply to those tools. Convertessa bundles and distributes no media codec; conversions run through the tools you install on your own device.
Open-source acknowledgements
Convertessa relies on the work of many open-source developers. Beyond the tools listed above, we acknowledge the broader ecosystems that make them possible, including:
- The FFmpeg contributors and the decades of work on open multimedia infrastructure.
- The libvips team for an exceptionally fast image-processing library.
- The libraw team for camera RAW decoding support in libvips.
- ImageMagick Studio LLC and the ImageMagick contributors for the ImageMagick library linked by libvips.
- The OpenSlide team for whole-slide image support in libvips.
- John MacFarlane and the pandoc contributors for a universal document converter.
- The Document Foundation and LibreOffice community.
- Kovid Goyal and the Calibre contributors for making e-book management accessible.
- The fontTools contributors for the font-engineering toolkit behind Convertessa's font conversions.
- The libarchive contributors for the archive library underlying bsdtar.
- Helmut K. C. Tessarek for providing and maintaining pre-built FFmpeg macOS binaries (GPLv3 builds for macOS).
- The Sparkle Project contributors for the software-update framework.
Your responsibilities
You must ensure you have the rights to convert the files you process with Convertessa. Convertessa does not authorise copyright infringement, circumvention of DRM or technical protection measures, or any unlawful copying. Convertessa does not remove or bypass DRM; where a tool detects DRM-protected content, Convertessa surfaces that error and stops.
Contact
Questions about licensing or open-source compliance? Email support@convertessa.app.