Discord captures audio at the application level by inserting a DLL with a hook on the relevant system calls. This works remarkably well, all things considered,

Discord captures audio at the application level by inserting a DLL with a hook on the relevant system calls. This works remarkably well, all things considered, but it does have a couple side effects, notably the fact that if you're not streaming at the application level, audio doesn't work (they could probably work around this if they wanted to, but it's basically a natural consequence), and the fact that some applications will become unstable or crash when being streamed. It also requires every anticheat ever to whitelist Discord's DLL.