Re: Device gone away notification?
Re: Device gone away notification?
- Subject: Re: Device gone away notification?
- From: Doug Wyatt <email@hidden>
- Date: Tue, 8 Sep 2009 11:43:41 -0700
Oddly enough, just the other day I was debugging something in this
area and thought it was odd that the HALOutput unit (a.k.a. AUHAL) was
dynamically choosing a new device if its current one went away. It
would be worth writing a bug about this.
The notification will not arrive on a realtime thread, and even if it
did, I think it would be okay for it to block, since at this time I
don't think anyone really cares if audio glitches -- you're trying to
stop.
Doug
On Sep 8, 2009, at 10:27 , Ethan Funk wrote:
I am using kAudioUnitSubType_HALOutput. I was expecting my I/O Proc
would just stop getting called, which would be fine, but instead,
the device seems to get re-directed to the system default device. I
will have a look at some of the notifications mention and see which
fits best. I assume the notifications will come in on a realtime
thread, so I will need to make sure the handler does not block,
correct?
Ethan...
On Sep 8, 2009, at 10:13 AM, Stephen Davis wrote:
If you are using kAudioUnitSubType_DefaultOutput, CoreAudio will
track the default device for you which sounds like the behavior
you're seeing. If you want to be tied to a particular device, you
use kAudioUnitSubType_HALOutput and tell it which device to use.
Off-hand, I'm not sure what happens when the device goes away but,
in the absence of any special handling by you, I suspect your I/O
proc will just stop getting called which is also what happens when
somebody else takes hog mode on the device you're using. I do not
know if it will come back but it should be pretty easy for you to
find out. As Brian said, you'll need to listen to notifications on
that device to find out when it goes away.
hth,
stephen
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