Question

I’m trying to synchronize a visualizer with an audio-track that’s being played with the generator audio unit, subtype audioFilePlayer in an AUGraph.

I would like to use Core Audio’s Clock API, but I there’s not much info out there. I found this, and this.

Does anyone know of a good example in english or any docs on this API?

Answer 1

The answer is that there is almost no documentation, and the only reference I found was an Apple list serv stating that it’s not a fully developed API.

Instead, if you need audio clock data, register a render callback with your generator audio unit like this.

AudioUnitAddRenderNotify(m_generatorAudioUnit, auRenderCallback, this);


OSStatus auRenderCallback (
                      void                        *inRefCon,
                      AudioUnitRenderActionFlags  *ioActionFlags,
                      const AudioTimeStamp        *inTimeStamp,
                      UInt32                      inBusNumber,
                      UInt32                      inNumberFrames,
                      AudioBufferList             *ioData
                      )
{      
    AudioEngineModel* pAudioEngineModel= (AudioEngineModel*)inRefCon;
    pAudioEngineModel->m_f64SampleTime= inTimeStamp->mSampleTime;

    return noErr;
}

You can get seconds by dividing the mSampleTime by the sampleRate.