Re: Question on aggregate device on Tiger
Re: Question on aggregate device on Tiger
- Subject: Re: Question on aggregate device on Tiger
- From: Jeff Moore <email@hidden>
- Date: Mon, 13 Jun 2005 12:09:18 -0700
On Jun 13, 2005, at 9:57 AM, Stéphane Letz wrote:
We define an aggregate audio device that combines the two internal
iMic USB devices (one is input only, the other is output only) so
that the iMic can be managed was a single device. Now is iMic is
disconnected from the machine, the aggregate still remains in the
system even it does not see any real device. Thus when asking the
standard property, we get unusual value like sample rate of 0...
and so on.
This is expected. An aggregate device is allowed to have an empty
active sub-device list.
I see that Audio/Midi setup application "filter" in some ways this
"lonely" aggregate audio device, and does not display is at all,
The Sound Prefs panel filters out devices that cannot be the default
device.
when HALLab display is with the 0 or empty parameters.
HALLab is there to show the HAL in it's naked glory, so it shows the
device.
Since this kind of behaviour is somewhat new in Tiger, it seems
that (possibly) a lot of applications will have to take care of
this strange kind of devices (possibly decide not to display them
in their list of available devices since the device cannot do
anything interesting....).
Is this what applications have to do?
It has always been what applications have to do. This is not new
behavior at all. An app should have always been prepared for devices
that have no streams or other unexpected configurations.
Could we imagine that the HAL could "filter" this kind of empty
aggregate device so that application code does not have to take
care of that?
How would an app interact with it to change it into a non-empty
aggregate if it can't find the device in the first place?
The right thing to do (and again this isn't new) is for apps to
filter the list themselves and display to the user only the devices
that the app is able and/or willing to work with.
--
Jeff Moore
Core Audio
Apple
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