Audio MixerUnit output writing problem.

Subject: Audio MixerUnit output writing problem.
From: JongYoung Park <email@hidden>
Date: Wed, 30 Dec 2009 13:30:29 -0600

Hello, Lists members.

I'm making sound mixing program in iPhone based on Apple mixer sample.

(iPhoneMultichannelMixerTest)

(Link : http://developer.apple.com/iphone/library/samplecode/iPhoneMultichannelMixerTest/index.html)

I want to make a file from mixer output, - Mixed sound from AUGraph- so I tried find infos in mailing list.

My conclusion was that I need something more to get result correct.

1. Make render callback for saving - using ExtAudioFileWrite -

2. Change final output unit from kAudioUnitSubType_RemoteIO to kAudioUnitSubType_GenericOutput.

3. Set render callback that I made before(1 step) to the kAudioUnitSubType_GenericOutput.

(ex.

AURenderCallbackStruct rcbs2;

rcbs2.inputProc = &renderOutput;

rcbs2.inputProcRefCon = mSoundBuffer;

OSStatus rst = AudioUnitSetProperty(mOutput,

kAudioUnitProperty_SetRenderCallback,

kAudioUnitScope_Output,

&rcbs2,

sizeof(rcbs2));

)

4. Call AudioUnitRender to work AUGraph flow. (Can't use AUGraphStart() because it did not happen nothing)

OSStatus rst = noErr;

int FRAMES = 512;

// render settings

AudioTimeStamp timestamp;

timestamp.mSampleTime = 0;

timestamp.mFlags = kAudioTimeStampSampleTimeValid;

AudioBufferList bufferList;

bufferList.mNumberBuffers = 1;

bufferList.mBuffers[0].mNumberChannels = 1;

bufferList.mBuffers[0].mDataByteSize = FRAMES * 1 * sizeof (float);

while (1) { // only for Test

AudioUnitRenderActionFlags flags = 0;

result = AudioUnitRender(mOutput,

&flags,

&timestamp,

FRAMES,

&bufferList);

if (result) { printf("AURender result %d X %4.4s\n", result, result, (char*)&result); return; }

}

......

But unfortunately I received -50 error from AudioUnitRender function.

From here, my questions start.

1. Is my approach is correct to write a file from AUGraph?

2. If it is not, is there best way to get a result?

3. Can you give me a hint with sample code?

Thank you for reading.

-Abraham P.-

say, /i:badak/

http://www.ebadaq.com

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