Foleyix browser audio export uses @breezystack/lamejs 1.2.7, a JavaScript MP3 encoder by Alex Zhukov.

Source code: https://github.com/shijinyu/lamejs
License: GNU Lesser General Public License, version 3.0 (LGPL-3.0)
License text: https://www.gnu.org/licenses/lgpl-3.0.html

The library is loaded in a separate browser Web Worker. The library's upstream license notice follows.

Can I use LAME in my commercial program?

Yes, you can, under the restrictions of the LGPL. The easiest way to do this is to link to LAME as a separate library, acknowledge its use and provide a link to lame.sourceforge.net. If you make modifications to LAME, you must release those modifications under the LGPL.