mediabunny-mp3-encoder.min.js is the unmodified bundle from the npm package @mediabunny/mp3-encoder 1.59.1.
The wrapper is under the Mozilla Public License 2.0 (LICENSE). It contains the LAME MP3 encoder compiled to
WebAssembly, under the GNU Lesser General Public License, version 2 or later (LICENSE-LAME-LGPL-2.0).

Corresponding source:
  wrapper and build   https://github.com/Vanilagy/mediabunny (tag v1.59.1)
  LAME                https://lame.sourceforge.io/download.php

ToolRecipe only loads this file at run time and calls it; it is not merged into other code.
You may replace it with your own build.