I discovered after doing a little bit of browsing on the OBS forums that a proper plugin for pipewire audio capture exists (that is in the process of getting merged into the overall OBS project), which handles not only application audio capture but input and output devices as well. This script will continue to exist as my own learning experience but do note that a proper solution exists.
A super scuffed script that attempts to make capturing specific application audio easier. By all practicality just a bunch of automated pw-cli calls, I am unfortunately not well-versed with C++ at the moment and do not have time (woohoo finals season) to work on a full-blown plugin. Note that currently all output nodes with a shared name will be captured (i.e. all audio outputs with the name 'Firefox'). This is intentional since my personal use-case is capturing game audio, which will often have multiple outputs created for some reason. I may add it as an option at some point but right now cannot be bothered
As the name implies, you need to be using PipeWire as your audio backend for this script to function. Additionally, your session manager must be WirePlumber as the script relies on some of its functionality (particularly its scripting engine).
Note: "OBS Pipewire Audio Capture Monitor" must be added as a global audio device under the audio settings for sound to be properly captured
Node names to connect. Currently filters out any pipewire nodes that are not of media.class
Updates on save.
Stream/Output/AudioAudio/Source
Currently this whitelist can be edited by editing pwinterface.lua, though I will likely decouple this hard-coded whitelist from the script in the future.
Volume of the source's capture. Updates live.
When a new audio source with the same name is created automatically connect the new node to the capture. Useful for when re-opening applications or in browsers. Updates on save.