Okay, so the most sensible option, which I have successfully confirmed to work, is to use OGG Vorbis, package the codec with the runtime, and call it there.
Opus sits right on the edge of niche, and there were way too many technical difficulties getting that format to behave with my compiler and build system. Meanwhile, Vorbis has just a few more advantages over MP3.
That being said, though, if Vorbis would have also failed me, then I was planning to go with MP3.
Thanks again, everyone!