Browser video tools use @ffmpeg/ffmpeg 0.12.15 (MIT) and @ffmpeg/core 0.12.10 (GPL-2.0-or-later).
The core is loaded as a separate WebAssembly engine. Source, build scripts and component licenses:
https://github.com/ffmpegwasm/ffmpeg.wasm/tree/v0.12.10
https://www.ffmpeg.org/legal.html