It's headerless mono psx adpcm, pretty sure changing the extension from .str to .vb will work fine w/ vgmstream. A basic txth would suffice if you do not want to mess with extensions (just name it .str.txth):
I prefer requests to go in their own threads rather than cluttering that one, which I think should just be for announcements (or bugs).
Not that my opinion matters as I'm not working on vgmstream any more.
by AnonRunzes at 10:22 AM EDT on September 30, 2019
to be honest, saying that someone out there is cluttering this board with "threads for these kinds of requests" kinda defeats the point of having an entire message board dedicated to sound formats and just video game music in general, but if that said someone decides to request a sound format to be added in vgmstream on a vgmstream-specific thread then it's all a matter of luck over whether or not that said someone is even going to get a reply regarding that request, if at all.