Re: 'ahal' unit vs. 'def ' question
Re: 'ahal' unit vs. 'def ' question
- Subject: Re: 'ahal' unit vs. 'def ' question
- From: Brad Ford <email@hidden>
- Date: Mon, 22 Mar 2004 11:08:42 -0800
Hi Stephen,
Do you need to support multiple output devices simultaneously? Do you
need to support playing to an output device that is not (or cannot be)
the default output device? If so you need to use the au hal output
unit. The difference with this guy is that it doesn't follow the
default output device when the default output device changes, i.e. if
someone changes the Default Output Device in Audio Midi Setup.app.
Beyond that, their behavior is essentially the same. Don't know about
the 10.1.5 question.
-Brad Ford
QuickTime Engineering
On Mar 22, 2004, at 10:45 AM, Stephen Davis wrote:
What's the difference? If I want to support multiple output devices
but still want to use the output unit interface so I can tell it what
format I have instead of matching our output to its format, is there
any reason to use 'ahal' vs. 'def ' or vice-versa? Assuming I set the
kAudioOutputUnitProperty_CurrentDevice property of course.
The docs imply that they are not the same but opening the 'ahal' and
giving it audio data that doesn't match the hw (8 kHz mono) seems to
work just fine so it appears to be doing everything the 'def ' unit is
documented to do as far as format conversion goes.
Further, if I do use the 'def ' device and set its "current device"
property, will that change out from under me if the user changes the
output device in the sys prefs? The wiki page at
http://www.mat.ucsb.edu:8000/CoreAudio/16 says that the 'def ' device
will switch away from you but the 'ahal' one won't.
Finally, out of all these questions/answers, which do or do not apply
on Mac OS X 10.1.5? I need to know if the same code will work from
10.1.5 on or if I need to special-case any of this.
thanks,
stephen
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