Using ExtAudioFileWriteAsync() in callback function. Can't get to run

Question

Just can\'t seem to get very far in Core Audio. My goal is to write captured audio data from an instrument unit to a file. I have set up a call to a callback function on an inst

Answer 1

Here's the working callback for a 16-bit linear big-endian stereo AIF file:

OSStatus MyRenderProc(void *inRefCon,
                  AudioUnitRenderActionFlags *ioActionFlags,
                  const AudioTimeStamp *inTimeStamp,
                  UInt32 inBusNumber,
                  UInt32 inNumberFrames,
                  AudioBufferList * ioData)
{
    SInt16 samples[inNumberFrames + inNumberFrames];
    AudioBufferList bufferList;
    bufferList.mNumberBuffers = 1;
    bufferList.mBuffers[0].mData = samples;
    bufferList.mBuffers[0].mNumberChannels = 1;
    bufferList.mBuffers[0].mDataByteSize = (inNumberFrames + inNumberFrames) * sizeof(SInt16);

    Float32 *leftData = (Float32 *)ioData->mBuffers[0].mData;
    Float32 *rightData = (Float32 *)ioData->mBuffers[1].mData;

    if (*ioActionFlags & kAudioUnitRenderAction_PostRender){
        static int TEMP_kAudioUnitRenderAction_PostRenderError = (1 << 8);
        if (!(*ioActionFlags & TEMP_kAudioUnitRenderAction_PostRenderError)){
            for (UInt32 i = 0; i < inNumberFrames; i++) {
                samples[i + i] = CFSwapInt16HostToBig((SInt16) SHRT_MAX * (leftData)[i]);
                samples[i + i + 1] = CFSwapInt16HostToBig((SInt16) SHRT_MAX * (rightData)[i]);
            }
        CheckError(ExtAudioFileWriteAsync(testRecordFile, inNumberFrames, &bufferList), "ExtAudioFileWriteAsync failed");
        }
    }
    return noErr;
}