[wdmaudiodev] Re: Changing device format
- From: "Cheng-mean Liu (SOCCER)" <soccerl@xxxxxxxxxxxxx>
- To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Wed, 17 Jun 2009 18:12:20 -0700
Windows 7 supports dynamic device format change, here is some information on
this feature.
Dynamic Format Change Support
Before Windows 7, once an audio driver was loaded there was no way for
drivers to notify the audio stack that its format capabilities had changed and
needed to be reparsed without unloading and reloading the driver. This caused
some issues in scenarios such as the following:
* There are audio devices that come with the capability to dynamically
change their supported formats via hardware buttons/switches on the device.
Users needed to unload and reload the driver to get the new capabilities before
Windows 7.
* The supported formats available to an HDMI audio endpoint are related
to the active display mode. When switching display modes, HDMI endpoints would
end up with an incorrect list of supported formats if the driver was not
unloaded and reloaded.
* Some SysFX APOs that come with 3rd party driver packages might add new
device format such as AC3 in an encoding APO. However, when this APO was
disabled (most likely from the UI), the lack of supported format change
notification would cause the wrong supported format list to be exposed.
For above reasons, the support for Dynamic Format Change was added to Windows 7.
There are two methods for triggering the audio stack to re-evaluate a
device's format capabilities. One method is for the driver to initiate a KS
event. The KSEVENT_PINCAPS_FORMATCHANGE event in event set
KSEVENTSETID_PinCapsChange was created for audio drivers to notify the audio
stack of a device format capability change. (See
http://msdn.microsoft.com/en-us/library/dd573912.aspx
for details). The other method is through the IAudioEndpointFormatControl
interface on the endpoint for MMDevApi applications. The MMDevApi clients (like
an IHV's APO) can call IAudioEndpointFormatControl:: ResetToDefault on an
endpoint to request the audio stack to re-evaluate an endpoint's device format
capabilities. For more IAudioEndpointFormatControl details, see MSDN
http://msdn.microsoft.com/en-us/library/dd408145(VS.85).aspx
">> If not, how are HDMI Audio Sinks properly supported?"
This is exactly how HMDI dynamic format is supported in Windows 7 HD Audio
Class Driver.
Cheng-mean Liu
-----Original Message-----
From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of AI Developer
Sent: Wednesday, June 17, 2009 3:44 AM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: Changing device format
Hi Uwe,
That (dynamically adding/removing subdevices) is what we're doing now,
but I was hoping for a better/cleaner approach, specially since Hakon
had referred to it in this post.
Thanks.
Devendra.
uwekirst wrote:
> I think seting the format is similar to settings the sampling
> frequency, both is not possible any longer within Vista.
> If you are looking through this list, you will find a possible
> solution (from the point of view of the driver developer): Dynamically
> install different drivers, each one supports one format (or sf) only.
> Its also possible to install/uninstall subdevices (no need to install
> the complete driver).
> /Uwe
>
>
> AI Developer schrieb:
>> Looking through the list archives, I saw this posting (from Oct. 2007):
>>
>>> There is no supported/documented way to set the default device format
>>> programmatically/dynamically from the device on Vista. This is a user
>>> only setting on this OS version.
>>>
>>> There have been many requests for this design to change and we are
>>> looking into this for the next version of Windows (no - the next
>>> version
>>> of Windows does not mean Service Pack 1) especially since it will be
>>> required to properly support HDMI Audio sinks.
>>>
>>> HakonS, Windows Sound Team PM
>>>
>> Has this been done yet?
>>
>> If yes, what's the mechainsm?
>>
>> If not, how are HDMI Audio Sinks properly supported?
>>
>> Thanks.
>> Devendra.
>>
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