KC / OPEN SOURCE
Open-source software in KC.
KC for Mac includes the open-source components below. Here are their licenses, the exact source KC builds from, KC’s changes and the build scripts.
Updated: October 20, 2026 · KC 1.0
AT A GLANCE
Five components, two with KC patches.
FFmpeg and FFmpegKit are under the GNU LGPL 3.0 and ship as separate dynamic libraries; OpenSSL is under the Apache License 2.0, the Mozilla CA bundle under the MPL 2.0 and Sparkle, which installs updates in the Mac app, under the MIT License. KC’s own code is not open source.
FFmpeg 9.0.1 · LGPL 3.0 or later
The audio and video libraries (libavcodec, libavformat, libavfilter, libavdevice, libavutil, libswresample, libswscale). Configured with --enable-version3 and without --enable-gpl or --enable-nonfree, so the GNU LGPL 3.0 applies. KC changes one thing: HTTP requests may only go to the HTTPS hosts KC allows for the current export.
FFmpegKit Next 9.0.0 · LGPL 3.0
The framework that runs FFmpeg inside the app (ffmpegkit.framework). KC changes one thing: failure logs leave out command arguments and exception details, so no video addresses end up in logs.
Source: arthenica/ffmpeg-kit-next, tag v9.0.0, commit a724ed99 ↗ KC’s patch: ffmpegkit-redact-args.patch (SHA-256 b5389236…2c5611b8)OpenSSL 3.5.7 · Apache 2.0
TLS for FFmpeg’s HTTPS requests, built into the FFmpeg libraries. Not modified.
Source: arthenica/openssl, commit 8cf17aae ↗ Apache License 2.0Mozilla CA certificate bundle (2026-08-13) · MPL 2.0
The certificate authorities FFmpeg trusts for HTTPS (cacert_2026_08_13.pem). Not modified.
Source: arthenica/ffmpeg-kit-next-test, tag v9.0.0 ↗ Mozilla CA bundle license (MPL 2.0)Sparkle 2.10.1 · MIT
Installs updates in the Mac app (Sparkle.framework, KC.app/Contents/Frameworks): when you choose Install and Relaunch in KC’s update alert, it downloads the new version, checks its signature, replaces KC and opens it again. It never checks for updates on its own. Not modified.
Source: sparkle-project/Sparkle, tag 2.10.1, commit ab7d7129 ↗ Sparkle license (MIT, with the code it bundles)How KC builds them
These scripts fetch the exact commits above, apply the two patches and build the libraries with the same flags as the app (--enable-lib-openssl -x --no-bitcode, iOS 15 and Mac Catalyst 15 targets, Xcode 27). The Mac app uses the Mac Catalyst arm64 build.
The licenses, a copy of the source, and replacing the libraries
FFmpeg and FFmpegKit are separate dynamic libraries in KC.app/Contents/Frameworks, and the GNU LGPL 3.0 lets you replace them with your own build. The full license texts are also in the app, under Settings → Help and info → Open-source licenses. If you would like a copy of the complete corresponding source from us, ask through Contact support at the top of this page or from the app’s Help center → Report a problem; this offer is valid for at least three years after the last KC version that includes these libraries.