Reality Check: UMDF filter for audio capture

Hi,

I'm new to device driver programming. The original idea was to write a
filter driver in kernel mode for my application, but now I know enough that
anything kernel mode is not child's play... so if I can stay away from it I
will.

I found that UMDF filter drivers are much safer (and therefore faster to
develop) than KM drivers, so before I dive into learning it, let me check if
what I want to do is feasible.

Basically, I want to tap into the playback stream of an audio device. I've
been doing audio recording for the last decade using the windows multimedia
api, but that only works for the input channels (mic and line in for
example).
The application requirements dictate that not only I have to capture the
audio output from a playback channel, but also mix in audio into it.

Can we do it using UMDF? If yes, what is the catch? How far back can I go in
terms of platform (win2K would be nice, but we are probably willing to
sacrifice it - XP mandatory - in lieu of greater productivity/driver
reliability).

Any help appreciated.

Cheers

Padu

sorry, can't use UMDF for your task

d

--

This posting is provided "AS IS" with no warranties, and confers no rights.


"Padu" <> wrote in message
news:BE6D2FC8-3267-4841-8CFC-...
> Hi,
>
> I'm new to device driver programming. The original idea was to write a
> filter driver in kernel mode for my application, but now I know enough
> that anything kernel mode is not child's play... so if I can stay away
> from it I will.
>
> I found that UMDF filter drivers are much safer (and therefore faster to
> develop) than KM drivers, so before I dive into learning it, let me check
> if what I want to do is feasible.
>
> Basically, I want to tap into the playback stream of an audio device. I've
> been doing audio recording for the last decade using the windows
> multimedia api, but that only works for the input channels (mic and line
> in for example).
> The application requirements dictate that not only I have to capture the
> audio output from a playback channel, but also mix in audio into it.
>
> Can we do it using UMDF? If yes, what is the catch? How far back can I go
> in terms of platform (win2K would be nice, but we are probably willing to
> sacrifice it - XP mandatory - in lieu of greater productivity/driver
> reliability).
>
> Any help appreciated.
>
> Cheers
>
> Padu

Ouch...

Care to elaborate? Any alternative other than a KM filter driver?

Cheers

directshow might be an option, I am not familiar enough with the audio
infrastructure to give you a definitive answer

d

--

This posting is provided "AS IS" with no warranties, and confers no rights.


"Padu" <> wrote in message
news:0F5BAF3D-B807-435E-8FE0-...
> Ouch...
>
> Care to elaborate? Any alternative other than a KM filter driver?
>
> Cheers
>

> Can we do it using UMDF? If yes, what is the catch? How far back can I go in
> terms of platform (win2K would be nice, but we are probably willing to
> sacrifice it - XP mandatory - in lieu of greater productivity/driver

Be prepared for absolutely new audio architecture in Vista+

In Vista+, your only option is to write a user-mode plugin DLL to the central audio process called APO (Audio Processing Object).

In Vista+, the kernel code sometimes does not even sees the audio wave data as IRP+MDL - the DMA buffer of the soundcard's driver is directly mapped to the audio process, it fills the buffer with data and then sends the "production mark advance" message to the kernel land.

--
Maxim S. Shatskih
Windows DDK MVP

http://www.storagecraft.com

"Padu" <> wrote:
>
>Basically, I want to tap into the playback stream of an audio device. I've
>been doing audio recording for the last decade using the windows multimedia
>api, but that only works for the input channels (mic and line in for
>example).
>The application requirements dictate that not only I have to capture the
>audio output from a playback channel, but also mix in audio into it.

Unfortunately, pre-Vista and post-Vista require two completely different
approaches for this.

On XP and before, you can do this with an upper filter on your audio
device. It isn't easy, because you have to intercept and parse the KS
ioctl stream to determine the format and grab the data, but with a KMDF
driver it's not too bad.

On Vista, audio stack is almost completely redesigned. Old drivers still
work, but any HDAudio device (which means most motherboard audio) uses the
WaveRT driver model, where the audio never passes through kernel at all.
Instead, you can write a GFX APO, which is a user-mode DLL that lives in
the special audio engine process. The difficulty there is installation;
it's not hard to do for your own experiments, but it's more difficult for
production. There's a good white paper on the topic here:

http://www.microsoft.com/whdc/device/audio/sysfx.mspx

>If yes, what is the catch? How far back can I go in
>terms of platform (win2K would be nice, but we are probably willing to
>sacrifice it - XP mandatory - in lieu of greater productivity/driver
>reliability).

The filter driver works on 2K and XP. The APO works on Vista and beyond.
--
Tim Roberts,
Providenza & Boekelheide, Inc.