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Re: Capturing Data coming OUT of an AUGraph
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Re: Capturing Data coming OUT of an AUGraph

I did wonder about adding an additional bus output to my Matrix mixer (getting the same data as the output feeding the output device. This might actually be better for me anyway.

This could be fed to an output unit of type 'kAudioUnitIO_HALOutput' - perhaps this AU can be used to gather the data. Anyone have any info on this type of output unit ?

I do just want to fill a buffer, but there is very little documentation, it would seem for this type of thing.

I dont have the expertise to setup a complex AU chain manually, so I am relying on the simplicity of AUGraph, but just accessing the rendered data somehow.

I suppose this is exactly the same type of setup people would want to record the output of an AUGraph to disk, or for complex metering of output data. I actually want to feed the output data back to the input stage (muted, but dont ask why !). Incidentally, I would be interested to know how I can calculate the latency between the input and output of my AUGraph such that I could compensate the output samples to be concurrent with those entering the AUGraph.

Any suggestions on calls to look for or example code would be appreciated.

Cheers

Mark.

At 1:05 pm +0100 19/2/05, pwicker wrote:
On Feb 19, 2005, at 12:30 PM, Mark Gilbert wrote:

Folks.

I have an AUGraph which is primarily data being pulled into a Matrix Mixer feeding an output device.

I want to 'tap into' the data which has been mixed and is on its way out, so I can record it to disk.

Is there a simple callback I can insert to get this data as it passes through, without radically rewiring my architecture ?

I don't know well the AUGraph so I may be wrong. As far as I know, you don't have such a callback. What you could do is write a special AU that you could insert in front of your graph. Within the Render callback of this AU you should pass the audio buffers to a worker thread using a non blocking FIFO or ring buffer. This worker thread would then write the audio to the disk. What you must never do is call a disk API from the render callback. I believe there's a sample code in the SDK which shows how to deal with a disk writer thread (DiskWriterAUGraph I think but not sure).


Thanks

Mark Gilbert.
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email@hidden
Tel: +44 208 340 5677
fax: +44 870 055 7790
http://www.gallery.co.uk
New Product ! - Zen MetaCorder
Location Sound Field Recorder
http://www.metacorder.info
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Do not post admin requests to the list. They will be ignored.
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References: 
 >Capturing Data coming OUT of an AUGraph (From: Mark Gilbert <email@hidden>)
 >Re: Capturing Data coming OUT of an AUGraph (From: pwicker <email@hidden>)



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