[wdmaudiodev] Re: XP buffer handling question
- From: "Michael R. Preston" <mpreston42@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Mon, 09 Dec 2002 09:28:34 -0800
Hi, Walter. Thanks for getting back to me.
Well, my filter driver is a kernel-mode driver (i.e. .SYS) being
installed in the "UpperFilters" section in the .INF file. Does that
make it a kernel streaming filter?
Mike
Walter Oney wrote:
> "Michael R. Preston" wrote:
>
>>OK. I figured out part of what's going on. So... I'm writing an
>>upper-level filter driver. Some applications use streaming buffers, and
>>some use a ring buffer. When an application uses a ring buffer, it only
>>calls IOCTL_KS_WRITE_STREAM once. It seems that the only way do some
>>intermediate processing on the audio stream (I'm just talking about the
>>ring buffer case) is to intercept the calls to IOCTL_KS_PROPERTY when
>>the app (or Windows) gets the position (Id=KSPROPERTY_AUDIO_POSITION),
>>and from the play and write pointers you can figure out what portion of
>>the buffer to process. Does that sound reasonable? I'm trying to do
>>some processing on the audio before it gets played by the lower-level
>>driver.
>>
>
> I'm going to go out on a limb here and expose my considerable (but
> monotonically decreasing) ignorance about streaming. It sounds to me as
> though you've built a WDM filter driver that sits in the stack above a
> kernel streaming filter. If so, you may have run afoul of the problem
> that the word "filter" is being used in two inconsistent ways in the
> DDK.
>
> A "kernel streaming filter" is really a WDM function driver that pairs
> with KSPROXY.AX in user mode to particpate in a filter graph. In WDM
> terms, the bus driver for this pseudo device is the software enumerator.
>
> There are no DDK samples for writing data transform filters. In fact,
> the DDK actively discourages people from trying to write them, and
> that's precisely the area that I'm currently coming up to speed on. You
> may have better luck using the Direct-X SDK to build a user-mode
> Direct-Show transform filter. The Direct-Show base classes provide a lot
> of support and documentation for how to do that.
>
> --
> Walter Oney, Consulting and Training
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--
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| Mike Preston | Home: (360)756-1655 |
| E-mail: mpreston42@xxxxxxxxx | Cell: (360)303-9331 |
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| -- Alan Ashley-Pitt |
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