Defined in carb/audio/AudioTypes.h

constexpr size_t carb::audio::kInvalidDeviceIndex = ~0ull

special value for DeviceCaps::index to indicate that a real audio device is not currently selected for output.

When this value is present, a streamer output is in use instead. This value will only ever be set on the DeviceCaps object returned in the result of the IAudioPlayback::getContextCaps() function.