Apple

On Tue, Nov 15, 2011 at 2:30 PM, Seth Willits <email@hidden> wrote:

I'm opening the AudioOutputUnit and setting that up to write the audio out to a file. So one of the steps in that process (the last one below), is to get the number of frames in the audio buffers, using a simple AudioUnitGetProperty, but for one particularly user of my code, doing so fails with the error kAudioUnitErr_InvalidProperty.

Any idea why?

Is there another way I should be figuring out how big to make the AudioBufferList?

Code mostly in its entirety just incase it's something I did along the way:

// Open the AudioOutputUnit

description.componentType = kAudioUnitType_Output;

description.componentSubType = kAudioUnitSubType_HALOutput;

description.componentManufacturer = kAudioUnitManufacturer_Apple;

description.componentFlags = 0;

description.componentFlagsMask = 0;

if ((component = FindNextComponent(NULL, &description))) {

err = OpenAComponent(component, &mAudioOutputUnit);

...

}

// Enable input on the AUHAL

param = 1;

err = AudioUnitSetProperty(mAudioOutputUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, 1, &param, sizeof(UInt32));

// Disable Output on the AUHAL

param = 0;

err = AudioUnitSetProperty(mAudioOutputUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, 0, &param, sizeof(UInt32));

// Set the current device to the default input unit.

err = AudioUnitSetProperty(mAudioOutputUnit, kAudioOutputUnitProperty_CurrentDevice, kAudioUnitScope_Global, 0, &mInputDeviceID, sizeof(AudioDeviceID));

// Get the audio format of the input device

param = sizeof(AudioStreamBasicDescription);

err = AudioUnitGetProperty(mAudioOutputUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 1, &mDeviceFormat, &param);

// Set the format the AudioOutputUnit will output data in

...

err = AudioUnitSetProperty(mAudioOutputUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 1, &mOutputFormat, sizeof(AudioStreamBasicDescription));

// Get the number of frames in the IO buffer(s)

param = sizeof(UInt32);

err = AudioUnitGetProperty(mAudioOutputUnit, kAudioDevicePropertyBufferFrameSize, kAudioUnitScope_Global, 0, &numFramesInBuffer, &param);

/********* FAILS WITH kAudioUnitErr_InvalidProperty *****/

I'm asking for the number of frames in the buffers because I use that to calculate how big the buffers that I allocate should be. (number of bytes per frame * number of frames in buffer). That comes straight out of the Apple sample code:

http://developer.apple.com/library/mac/#samplecode/RecordAudioToFile/Listings/DCAudioFileRecorder_cpp.html

--
Seth Willits

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References:
	>Getting Failure from kAudioDevicePropertyBufferFrameSize (From: Seth Willits <email@hidden>)
	>Re: Getting Failure from kAudioDevicePropertyBufferFrameSize (From: kamaldeep tumkur <email@hidden>)