Is there any open source spatial audio thing out there? Or is everything just some proprietary magic with a brand like Dolby?
opus has an ambisonics profile: * https://datatracker.ietf.org/doc/html/rfc8486 * https://jmvalin.ca/opus/opus-1.3/
Ambisonics essentially asks the question of "what if we also stored a front-back and a top-bottom signal?" It turns out this is sufficient to fully represent 3D spatial audio. Additionally, unlike traditional "5.1/7.1"/etc. audio formats which assume a fixed speaker placement, digital signal processing can be used to adapt the audio to any number of speakers in any location in a space or use an HRTF to produce virtualized 3D audio for headphones.
Ambisonics had the misfortune of being invented in the 1970s before digital signal processing made the necessary audio signal processing for making practical use of it cheap and easy to implement, so inferior (but cheaper to implement) formats like Dolby Pro Logic ended up winning in both the consumer and professional spaces. From an open source perspective, though, this makes Ambisonics compelling because all of the important patents related to it should be well past their expiration by this point.