[wdmaudiodev] MMCSS and Audio over ethernet

  • From: AI Developer <developer@xxxxxxxxxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Fri, 16 Jul 2010 12:45:33 +0530

I'm currently working on an audio over ethernet solution, and am running into some issues related to how DPC latencies for the network stack change when audio playback is active.

Essentially, we have a proprietary protocol (not using tcp or udp), so, to send and receive raw ethernet packets, we've written an NDIS protocol driver.

This gets the work done, and seems to work okay on Windows XP.

On Windows 7 (and I assume Vista also) however, it all works fine until someone starts playing audio with Media Player (to another/built-in audio device).

As soon as Media Player audio playback starts, the network packet callbacks start getting delayed - sometimes by as much as 10 milliseconds.

From what I understand that this is related to the MMCSS telling the NDIS stack to defer it's processing.

In our case, however, audio is actually going over the NDIS stack, so we need to disable this mechanism, or at least get MMCSS to allow timely delivery of packets for our interface.

I tried setting the value for:

HKLM\Software\Microsoft\Windows NT\Currentversion\Multimedia\SystemProfile\SystemResponsiveness

to 100 (default was 20).

That seems to get rid of the problem. But I'm not sure if that's the right thing to do!

I'm looking for more insight/suggestions on what would be the best way to achieve this?


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