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Output AU buffer size for RenderCallback
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Output AU buffer size for RenderCallback


  • Subject: Output AU buffer size for RenderCallback
  • From: "Tim Dorcey" <email@hidden>
  • Date: Sun, 30 Oct 2005 11:03:42 -0800
  • Importance: Normal

I found mention in archives here that the value of "inNumberFrames" passed
to a RenderCallback for default Output Unit is determined by the attached
device's "I/O proc frame count."  Is this a property that clients can (or
should) change?

On my system, talking to "Built-in Audio," it seems to want about 12 msec
per render callback.  This is fine, and anything in the range < 100 msec
would be fine for my app.  Do I need to concern myself with getting
something outside that range, and how do I change it if so?

Also, I based my code on a "Quick and Dirty" example that was posted here,
which was nothing other than:
FindNextComponent()	kAudioUnitSubType_DefaultOutput
OpenAComponent()
AudioUnitSetProperty()	kAudioUnitProperty_StreamFormat
AudioUnitSetProperty()	kAudioUnitProperty_SetRenderCallback
AudioUnitInitialize()
AudioUnitStart()
...
AudioUnitStop()
AudioUnitUninitialize()
CloseComponent()

Then, my render callback simply fills the AudioBufferList presented to it.
Is that all there is to it?

Also, is it correct to presume that if I Open/Start multiple instances of
the Output AU, the audio streams will be mixed at final output?  And, each
could have a different stream format (e.g., sampling rate)?

Thanks,
Tim

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