Almost all of FileSorcery's code was written for FileSorcery. The exceptions, in full:
LAME (MP3 encoding)
MP3 files are encoded by LAME, via the lamejs JavaScript port (the @breezystack/lamejs fork, version 1.2.7, shipped verbatim at /js/vendor/lamejs.js). LAME is the open-source MP3 encoder from lame.sourceforge.io; the port lives at github.com/zhuker/lamejs. It is licensed under the GNU Lesser General Public License - the full text, with LAME's own usage notes, is at LICENSE-lamejs.txt. Like everything else here it runs entirely in your browser; your audio is encoded on your own machine.
Typefaces
The site sets its wordmark and headlines in Fraunces (by Undercase Type) and everything else in Instrument Sans (by Instrument). Both are licensed under the SIL Open Font License 1.1 and served from this site rather than from a font network: Fraunces license ยท Instrument Sans license.
Everything else
The converters, the detection, the page and the build are original to this project, and the site makes no requests to any third party.