[wdmaudiodev] Re: Shared mode recording doesn't work if CurrentCount is nonzero

  • From: Eugene Muzychenko <eugene@xxxxxxxxxxxxxx>
  • To: Matthew van Eerde <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Thu, 14 Aug 2014 23:42:28 +0700

Hello Matthew,

> I believe the intent of this audio subsystem check is to ensure
> it's not stepping on any DirectKS clients' toes.

What undesired could happen in such case? If a driver exposes a pin
supporting a single instance only, there is no problem. If a pin
exposed allows multiple instances, a driver knows how to handle them

> Can you help me understand the scenario that requires simultaneous
> DirectKS and audio subsystem clients for a given pin?

A simplest example is an ASIO application working with a plain WDM/KS
device without its proprietary ASIO driver. In such case, ASIO4ALL
proxy is used, becoming a KS client. Since ASIO4ALL allocates the
first pin instance, no MME, DirectSound or WASAPI clients can access
the pin. The only workaround is to start MME/DirectSound/WASAPI client
first and then start ASIO client.

Some applications offer their own KS interfaces for recording to
ensure reliability (WASAPI exclusive mode implementation has at least
one known bug in Win7 that had been fixed in Win8).



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