Registers a callback to be called to allow the game to access metering data from any mixing bus. You may use this to monitor loudness at any point of the mixing hierarchy by querying the peak, RMS, True Peak and K-weighted power (according to loudness standard ITU BS.1770). See 使用 Speaker Matrix Callback 定制高级混音 for an example. The callback must be registered once per bus ID. Call with in_pfnCallback = NULL to unregister.
Note: The bus in_busID needs to be a mixing bus.
||Bus ID, as obtained by GetIDFromString( bus_name ).