A virtual driver installs a kext that appears to the system as a real audio device. But instead of talking to hardware, its Read() method writes audio into a circular buffer. Another app reads from that buffer.
At first glance, changing the volume on a MacBook is trivial: press a key, watch the icon bounce, and sound comes out. However, beneath this simplicity lies a layered, real-time software stack that is a marvel of systems engineering. The macOS audio driver is not a single file but an ecosystem of kernel extensions (kexts), user-space daemons, and hardware abstraction layers. macbook audio driver
Resetting the audio driver without rebooting: A virtual driver installs a kext that appears