This site uses the LAME MP3 encoder (https://lame.sourceforge.io), compiled unmodified to WebAssembly
by @mediabunny/mp3-encoder and loaded at run time as its own file (assets/mediabunny-mp3-encoder-*.js).
LAME is licensed under the GNU Lesser General Public License, version 2 or later:
https://www.gnu.org/licenses/old-licenses/lgpl-2.0.html  Source: https://lame.sourceforge.io/download.php
You may replace that file with your own build of LAME.

libheif (via libheif-js, used by heic-decode) is licensed under LGPL-3.0 (see libheif-js-LGPL-3.0.txt),
used unmodified and loaded at run time as its own file (assets/heic-decode-*.js).
Source: https://github.com/catdad-experiments/libheif-js and https://github.com/strukturag/libheif