Supporting Non-PCM Wave Formats
In Microsoft Windows 2000 and Windows 98, the WDM audio framework did not allow Windows clients to use the standard audio APIs (waveOut, DirectSound, and DirectShow) to play non-PCM audio data through the PortCls system driver.
This limitation has been removed in Microsoft Windows XP and later, and Windows Millennium Edition, which can play audio data encoded in a non-PCM format such as AC-3 or WMA Pro. In addition, a hot-fix package is available for Windows 98 SE that contains all fixes necessary to play non-PCM data through the waveOut and DirectSound APIs. Service Pack 2 for Windows 2000 also contains these fixes.
This section describes limitations in earlier versions of Windows that prevented clients from playing non-PCM audio, and presents a set of guidelines for adapting a WDM audio driver to support non-PCM data formats on more recent versions of Windows.
Additionally, this section describes the new subformat GUIDs in Windows 7 that provide support for compressed audio formats.
This section includes the following topics: