Click During Inter-App Audio Recording - ios

Question

I have been attempting to recording my input during an inter-app audio session on iOS 9. The speaker output sounds fine but the recorded file has a rhythmic clicking sound.
The waveform looks like below...
I have tweaked every setting and parameter I can think of and nothing seems to work.
Here are the format settings (stream settings are identical)...
AudioStreamBasicDescription fileFormat;
fileFormat.mSampleRate = kSessionSampleRate;
fileFormat.mFormatID = kAudioFormatLinearPCM;
fileFormat.mFormatFlags = kAudioFormatFlagsNativeFloatPacked;
fileFormat.mFramesPerPacket = 1;
fileFormat.mChannelsPerFrame = 1;
fileFormat.mBitsPerChannel = 32; //tone is correct but there is still pops
fileFormat.mBytesPerPacket = sizeof(Float32);
fileFormat.mBytesPerFrame = sizeof(Float32);
Here are the stream settings...
//connect instrument to output
AudioComponentDescription componentDescription = unit.componentDescription;
AudioComponent inputComponent = AudioComponentFindNext(NULL, &componentDescription);
OSStatus status = AudioComponentInstanceNew(inputComponent, &_instrumentUnit);
NSLog(#"%d",status);
AudioUnitElement instrumentOutputBus = 0;
AudioUnitElement ioUnitInputElement = 0;
//connect instrument unit to remoteIO output's input bus
AudioUnitConnection connection;
connection.sourceAudioUnit = _instrumentUnit;
connection.sourceOutputNumber = instrumentOutputBus;
connection.destInputNumber = ioUnitInputElement;
status = AudioUnitSetProperty(_ioUnit,
kAudioUnitProperty_MakeConnection,
kAudioUnitScope_Output,
ioUnitInputElement,
&connection,
sizeof(connection));
NSLog(#"%d",status);
UInt32 maxFrames = 1024; //I tried setting this to 4096 but it did not help
status = AudioUnitSetProperty(_instrumentUnit,
kAudioUnitProperty_MaximumFramesPerSlice,
kAudioUnitScope_Output,
0,
&maxFrames,
sizeof(maxFrames));
NSLog(#"%d",status);
_connectedInstrument = YES;
_instrumentIconImageView.image = unit.icon;
NSLog(#"Remote Instrument connected");
status = AudioUnitInitialize(_ioUnit);
NSLog(#"%d",status);
status = AudioOutputUnitStart(_ioUnit);
NSLog(#"%d",status);
status = AudioUnitInitialize(_instrumentUnit);
NSLog(#"%d",status);
[self setupFile];
Here is my callback...
static OSStatus recordingCallback(void *inRefCon,
AudioUnitRenderActionFlags *ioActionFlags,
const AudioTimeStamp *inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList *ioData)
{
ViewController* This = This = (__bridge ViewController *)inRefCon;
if (inBusNumber == 0 && !(*ioActionFlags & kAudioUnitRenderAction_PostRenderError))
{
ExtAudioFileWriteAsync(This->fileRef, inNumberFrames, ioData);
}
return noErr;
}
Full view controller code here
Thanks for your help.

Answer 1

You are writing to file pre and post render. In your render callback, change your if statement to only write on post render.
if (inBusNumber == 0 && *ioActionFlags == kAudioUnitRenderAction_PostRender){
ExtAudioFileWriteAsync(This->fileRef, inNumberFrames, ioData);
}
ExtAudioFileWriteAsync does some internal copying and buffering so it's fine to use in the render callback as long as you prime it before the first write.

Answer 2

Most likely you'll have to check for both:
post-render action flags
post render error
The critical part of your callback will probably have to look somewhat like this:
if (*ioActionFlags & kAudioUnitRenderAction_PostRender){
static int TEMP_kAudioUnitRenderAction_PostRenderError = (1 << 8);
if (!(*ioActionFlags & TEMP_kAudioUnitRenderAction_PostRenderError))
{
ExtAudioFileWriteAsync(This->fileRef, inNumberFrames, ioData);
//whichever additional code needed
// { … }
}