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KS Topology Considerations

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The WDMAud system driver (Wdmaud.sys) translates the KS-filter topology into the legacy mixer lines that are exposed through the mixer API. A non-PCM pin corresponds to a SRC line (MIXERLINE_COMPONENTTYPE_SRC_XXX) in the mixer API. If this pin is in a data path that eventually flows into a bridge pin (the physical connection at the endpoint of a graph) that is dedicated to non-PCM data, the mixer API exposes the bridge pin as an additional DST line (MIXERLINE_COMPONENTTYPE_DST_XXX), separate from the DST line for PCM data. This can add unnecessary complexity to the controls that are visible through a mixer-API client such as a replacement for the SndVol32 utility.

If you prefer not to expose a non-PCM pin in this manner, one approach is to make sure that the data path containing the pin eventually feeds into a SUM node that is shared by the PCM data path. That is, join the non-PCM DST line to the main DST line. Unfortunately, this workaround misrepresents the true hardware topology and might lead to future problems with clients that attempt to control the non-PCM data stream through nodes downstream from the SUM node. A better approach is to modify the mixer-API client to simply ignore SRC and DST lines that have no controls.

If you use the KsStudio utility to view your wave filter in KSCATEGORY_AUDIO, you should expect to see a separate pin for non-PCM data. When viewing the composite system audio graph under KSCATEGORY_AUDIO_DEVICE, you should see your non-PCM data ranges on the main wave-output pin, alongside any PCM data ranges.

SysAudio (Sysaudio.sys) is the system audio device in Windows Server 2003, Windows XP, Windows 2000, and Windows Me/98. Note that SysAudio generates KSCATEGORY_AUDIO_DEVICE automatically--a driver should not register itself manually in this category.

You are not required to connect a non-PCM data path to the Topology miniport driver. This connection is of benefit only if the non-PCM data path interacts with the rest of the device's topology; for instance, if it feeds into a common mixer or sample-rate converter. Connecting a streaming pin to a bridge pin, where both pins are on the wave miniport driver, forms a valid, complete topology for a non-PCM data stream that flows directly to an S/PDIF port, for example.