lamejs 1.2.7 (npm package @breezystack/lamejs), a JavaScript port of the LAME MP3 encoder.
License: GNU Lesser General Public License v3.0 (LGPL-3.0). Full texts: /licenses/LGPL-3.0.txt and /licenses/GPL-3.0.txt.

How Zebra Compress uses it: the file is used unmodified, as a separate file at /assets/compress/lame/lamejs-1.2.7.js, and is loaded only when
you compress audio to MP3. You may replace it with your own compatible build of lamejs (same file name and API:
lamejs.Mp3Encoder(channels, sampleRate, kbps), encodeBuffer, flush).

Source code: https://github.com/shijinyu/lamejs (a fork of https://github.com/zhuker/lamejs).
LAME project: https://lame.sourceforge.io

Notice shipped with the package:

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:

1. Link to LAME as separate jar (lame.min.js or lame.all.js)

2. Fully acknowledge that you are using LAME, and give a link
   to our web site, lame.sourceforge.net

3. If you make modifications to LAME, you *must* release these
   these modifications back to the LAME project, under the LGPL.