Getting the description of an AUHAL output node
Getting the description of an AUHAL output node
- Subject: Getting the description of an AUHAL output node
- From: Christopher Ashworth <email@hidden>
- Date: Mon, 24 Oct 2005 21:19:36 -0400
Hi.
I have set up an AUGraph with two nodes: an AUHAL output node and a
matrix mixer. My goal is to mix multichannel sound files out to
arbitrary output devices. Most of the steps in this process work. I
can select any given output device and mix the channels of the file
out to the device.
When hooking up the mixer to the AUHAL node, however, I seem to be
missing something about how to discover the stream description of the
output device so that I may match my mixer to it. For example, I
have an Edirol FA-101 output device connected via Firewire that has
up to 10 mono channel outputs, but I am only able to mix out to the
first two channels.
This page:
http://developer.apple.com/technotes/tn2002/tn2091.html#FORMATS
indicates to me that the AUHAL output node should "flatten" the
output data stream into a single stream with 10 channels. I would
then expect to be able to make the following call to determine the
stream format:
// Get the stream description of the output device.
size = sizeof(desc);
err = AudioUnitGetProperty( outDeviceUnit,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Output, // output
scope,
0, // on the
output bus
&desc,
&size );
This, however, produces the error result
kAudioUnitErr_FormatNotSupported.
None too confident that I really understand the proper combination of
scopes and elements, I tried the other three, but even when I do
successfully get a stream description back, it only contains two
channels. i.e. I can only mix my sounds out to two of the ten
available channels on my device.
Help?
Christopher Ashworth
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