Re: Controling CoreAudio device volume
Re: Controling CoreAudio device volume
- Subject: Re: Controling CoreAudio device volume
- From: Jeff Moore <email@hidden>
- Date: Mon, 4 Feb 2008 12:36:00 -0800
This question is completely orthogonal to your previous question.
Whether aggregate devices do or do not have any controls doesn't
really affect how an app should go about determining whether any
particular device has any particular controls. An app should always
use AudioObjectHasProperty to figure that out regardless of what kind
of device it is dealing with.
At any rate to answer this question, aggregate devices were originally
intended to be pure IO constructs. As such, doing things like changing
the volume on a channel or the sample format of a stream were
originally meant to be done on the underlying actual device. Since the
initial release we relaxed some of this strict treatment somewhat and
apps can now change the sample format of a stream on an aggregate
device.
At some point in the future, controls might show up on aggregates as
well (the feature request has been filed in Radar). This is why apps
should be using AudioObjectHasProperty() to determine whether or not
the device supports the control in question.
On Feb 4, 2008, at 12:10 PM, Stéphane Letz wrote:
------------------
Message: 3
Date: Mon, 4 Feb 2008 10:58:57 -0800
From: Jeff Moore <email@hidden>
Subject: Re: Controling CoreAudio device volume
To: CoreAudio API <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed;
delsp=yes
The "rules" are (and I'm not being facetious), if the device has a
control, you can use it. If it doesn't have one, you can't.
AudioObjectHasProperty() is your guide. This is true of every kind of
device the HAL supports.
OK, but then why for instance aggregate devices do not implement
AudioObjectHasProperty by redirecting it on the sub-devices?
--
Jeff Moore
Core Audio
Apple
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