[wdmaudiodev] Re: Capturing audio output

  • From: Hakon Strande <hakons@xxxxxxxxxxxxxxxxxxxxx>
  • To: <wdmaudiodev@xxxxxxxxxxxxx>, <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Sun, 16 Sep 2007 20:55:13 -0700

The audio driver does not (or at least is not supposed to) touch audio bits 
anymore in at least one major driver model (WaveRT) on Windows so in those 
cases filter drivers won't get to the audio data either.
Also, if the content that is playing is protected only signed and certified 
components can be part of the streaming pipeline so if your scenario requires 
real-time stream recording the content owner decides if your unsigned filter 
driver will be able to get insert itself in the pipeline.
So right there are two reasons a filter driver is not a one-size-fits-all 
solution or even a once-in-a-while solution.
What is the scenario your are trying to support? 
There may be another way to get a mix of the audio leaving the Windows audio 
system depending on what you are trying to do. If you are creating an AEC DMO 
for instance there is a format restricted loop back from the audio engine you 
can use.
Hakon Strande 
Program Manager - Windows Sound Team
Microsoft Corporation 


From: wdmaudiodev-bounce@xxxxxxxxxxxxx on behalf of Stefan
Sent: Sat 9/15/2007 10:28 AM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Capturing audio output

Hi, I known I'm not the first one to post this, but I want to be able to
capture the audio output and forward it to a user space app (XP/W2k).
I've googled, read the ddk docs, looked at source code for the last few
days but I'm still very confused. Right now I think the best way to do
this is to write a wdm filter driver that captures the output and
transfers it to a user space application. Is this even possible? And
where should I install the filter? I'm a very experienced coder, but I
need some guidance on where to start (i.e. "install a filer here and
listen on IRP x,y,z") and want to know if it's even possible.

Using the sound card output as input through the volume control isn't
good enough, and (correct me if I'm wrong) directshow filters doesn't
work on all sound output (applications using directsound for example).



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