New for Audio Drivers
In Windows 8, the audio engine has been redesigned to work with audio streams that have been offloaded to a hardware device that is separate from, but connected to, the computer's main audio system. This is referred to as hardware offloading.
The redesign involved adding new functionality to the Windows-provided Port Class audio driver (Portcls.sys), and the introduction of new properties, topology nodes, and structures for use by audio drivers. To complement these improvements in the audio driver, new interfaces have also been added to the set of core audio APIs.
New properties have been added to the KSPROPSETID_Audio property set:
A set of new properties has been added to the audio driver bag to accommodate hardware offloading. For more information about these new properties, see KSPROPSETID_AudioEngine.
To help offload-capable hardware devices to expose their offloading capabilities, a new topology node has been added to the set of nodes available for use by audio drivers. For more information about the new topology node, see KSNODETYPE_AUDIO_ENGINE.
New structures have been added to the set of audio driver structures, to work with the new properties:
And to support the new KSAUDIOENGINE_VOLUMELEVEL structure, the following new enumeration has been added:
New programming interfaces have been added to the set of core audio APIs: