Licensing & Open-Source Acknowledgements
This page describes how Convertessa works with third-party open-source tools, what licenses govern those tools, and the patent posture for the audio and video codecs 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.
- GPL and LGPL copyleft obligations do not extend to Convertessa. Invoking an external process is not distribution or linking of that process's source code. 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 | GNU LGPL version 2.1 or later (Homebrew default build includes libx264, which makes the Homebrew build as a whole GPL-2.0 licensed; the evermeet.cx build is also GPL-licensed — compiled with --enable-gpl --enable-libx264 --enable-libx265; verified at evermeet.cx/ffmpeg/ on 2026-06-11) |
| 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. Tischer and are not affiliated with the FFmpeg project. The evermeet.cx build is GPL-licensed (compiled with --enable-gpl --enable-libx264 --enable-libx265; verified at evermeet.cx/ffmpeg/ on 2026-06-11). 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 |
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.
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.
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.
Codec and patent posture
Some audio and video codecs are covered by patents held by patent pools or individual companies. The following table summarises the current status for the codecs Convertessa can process. This information is updated when the legal landscape changes.
| Codec | Posture | Notes |
|---|---|---|
| H.264 / AVC | ✅ Green — no royalty at current volume | Via-LA (formerly MPEG-LA) administers the AVC pool. The free tier covers PC software distribution up to 100,000 units at $0.00 royalty (confirmed May 2026 licence revision). Convertessa is well within this threshold. Source: via-la.com |
| H.265 / HEVC | Differentiated by operation |
HEIC still-image write (HEVC intra-frame encode): ✅ Green — routed through Apple's ImageIO framework ( HEVC video encode: Not currently offered — the HEVC video decode and HEIC read: Performed by the user-installed ffmpeg / libvips binaries (shell-out; Convertessa distributes no HEVC decoder). Patent pool exposure for software decoders in this architecture is low in practice; Convertessa does not bundle or distribute any HEVC decoding implementation. |
| E-AC-3 (Dolby Digital Plus) | ✅ Green — last patent expired | The last blocking US patent (US7516064) expired on 2026-01-30. No further E-AC-3 patents have been identified. Sources: Phoronix (2026-01-30), Fedora community discussion. |
| MPEG-4 Visual (Part 2) | ⚠️ Yellow until 2026-07-19, then Green | One Brazilian patent (BR PI0109962-0, Siemens AG) remains in force until 19 July 2026. After that date, MPEG-4 Visual is fully patent-free worldwide. This codec is rarely used today (superseded by H.264). Source: Wikimedia Meta |
| AV1 | Low risk | The Alliance for Open Media (AOMedia) patent pledge covers patents from its member organisations (including Google, Apple, Intel, Meta, Microsoft, Netflix). Sisvel asserts a separate pool of non-AOMedia patents; no enforcement actions against desktop software applications have been recorded as of 2026-06-11. |
| VP9 | Low risk | Google's VP9 patent pledge covers implementers. Sisvel asserts non-Google patents; no desktop software enforcement actions recorded as of 2026-06-11. |
| AAC | ✅ Green (primary encode paths via Apple AudioToolbox) |
mp4, mov, m4v, aac, m4a output: Convertessa explicitly passes mkv output: Audio is explicitly AC-3 ( No implicit ffmpeg-default AAC encoder is invoked on these targets. If the installed ffmpeg lacks AAC decode: User-installed ffmpeg default decoder (shell-out; Convertessa distributes no AAC decoder). Low risk. |
| MP3 | ✅ Green — all patents expired | The last MP3 patents expired by April 2017. No royalties or restrictions apply. |
| Opus / FLAC / Vorbis | ✅ Green — royalty-free | These codecs were designed to be royalty-free and are unencumbered by patent claims. |
Posture reflects Convertessa's specific architecture (shell-out to user-installed tools, no software codec bundling or distribution by Convertessa) and current published patent status. This is not legal advice; consult a lawyer for licensing decisions in your own products.
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.
- 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 libarchive contributors for the archive library underlying bsdtar.
- Helmut K. C. Tischer for providing and maintaining pre-built FFmpeg macOS binaries (GPL-licensed builds for macOS).
Contact
Questions about licensing or open-source compliance? Email support@convertessa.app.