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Re: clarification on RME suggestions ...
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Re: clarification on RME suggestions ...


  • Subject: Re: clarification on RME suggestions ...
  • From: John Lazzaro <email@hidden>
  • Date: Fri, 21 Jun 2002 14:35:22 -0700

> Jeff Moore writes:
>
> Apps should use kAudioDevicePropertyStreamConfiguration to get a
> picture of the channel layout of a device. This property returns an
> AudioBufferList that has the same structure as the one you will see in
> your IOProc except the actual pointers to the buffers will be NULL
> since this is for informational purposes.
>
> [...]
>
> Does this make it any clearer?

There's still an unsolved problem here, for the simple case of an
application that wants to send audio output to the speakers a human is
listening to, as the human indicates in the OS X Audio Preferences
pane.

Let's say the kAudioHardwarePropertyDefaultOutputDevice call, followed
by the kAudioDevicePropertyStreamConfiguration call, yields a device
with 4 mono streams.

In reality, the first two streams are the audio RCA jacks
from the soundcard (first left, then right), and the second
two streams are the S/PDIF jack for the soundcard
(first left, then right), and the user has chosen one of
these two logical I/O endpoints as her current default
using the OS X Audio Preferences pane.

As a naive app, though, all I see are 4 mono streams. I need to deduce
the following facts:

-1- That these four mono streams represent two stereo
logical I/O endpoints, not 4 mono logical I/O endpoints
or one 70's-retro quadrophonic endpoint :-).

-2- That the user, via the OS X preferences pane, has
chosen one of these logical I/O endpoints as the one
she wants to hear default audio from.

Those are the two discovery problems, and I'm looking for a general
algorithm that works for any compliant OS X CoreAudio hardware driver,
without needing to keep a database of manufacturer and product names
and stream organization.

Are these solvable discovery problems?

-------------------------------------------------------------------------
John Lazzaro -- Research Specialist -- CS Division -- EECS -- UC Berkeley
lazzaro [at] cs [dot] berkeley [dot] edu www.cs.berkeley.edu/~lazzaro
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