Re: IOAudioEngine::performFormatChange cannot be triggered by change of I/O Buffer Size
Re: IOAudioEngine::performFormatChange cannot be triggered by change of I/O Buffer Size
- Subject: Re: IOAudioEngine::performFormatChange cannot be triggered by change of I/O Buffer Size
- From: Jeff Moore <email@hidden>
- Date: Wed, 03 Dec 2008 22:49:11 -0800
That is more or less accurate. The thing to keep in mind here is that
your driver can have many clients. Each client can have a different
buffer size. This means that it probably isn't a good idea in general
to base any decisions on any one client's actions.
On Dec 3, 2008, at 9:46 PM, David Tan wrote:
Hi Jeff,
Thanks for your guides!
I also found another reply from you and Bill to some guy’s similar
question to me. I think I have general idea of this question.
Could you please review my understanding and let me any
misunderstanding? Thanks!
While one user-space application is attempting to play music through
my audio driver, Core Audio will cause the OS to call addClient().
Meanwhile the parameter “IOAudioClientBuffer* clientBuffer” will
give me information of application’s buffer settings. Is that correct?
Best Regards,
David Tan,
Software Engineer,
Dextrys Co., Ltd.
From: coreaudio-api-bounces+david.tan=email@hidden [mailto:coreaudio-api-bounces+david.tan=email@hidden
] On Behalf Of Jeff Moore
Sent: Wednesday, December 03, 2008 4:42 AM
To: CoreAudio-API Mailing List
Subject: Re: IOAudioEngine::performFormatChange cannot be triggered
by change of I/O Buffer Size
On Dec 2, 2008, at 12:22 AM, David Tan wrote:
On the device window of HALLab, there’re combo box of Nominal Sample
Rate and IO Buffer Size.
While I change the selection of Nominal Sample Rate, I can get
notification by IOAudioEngine::performFormatChange().
But it seems that change of IO Buffer Size cannot make it.
My question is: what’s the IO Buffer Size really means? Hardware or
driver?
That is the duration in sample frames of the IO cycle that the
application is requesting. It is wholly separate from the buffers in
the driver and the hardware.
And If I want to be informed in the driver of its change, which
method should I use.
About the only way you can monitor what buffer sizes the clients of
your driver are using, is to override IOAudioStream::addClient and
IOAudioStream::removeClient to observe as client buffers are
registered and unregistered.
--
Jeff Moore
Core Audio
Apple
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