I want to implement a volume level meter in CoreAudio using Swift

Question

I have looked into using installTap in AVAudioNode, but how can I get the volume level in real time in installTap in?

player.installTap(onBus: 0, bufferSize: 1024, format: player.outputFormat(forBus: 0)) { (buffer, when) in
    print(buffer.floatChannelData![0])
}

floatChannelData is a pointer to data but how to access real value?

Answer 1

Use floatChannelData pointer by dereferencing it and then accessing the individual samples.

player.installTap(onBus: 0, bufferSize: 1024, format: player.outputFormat(forBus: 0)) { (buffer, when) in
    let floatData = buffer.floatChannelData![0]
    let frameCount = Int(buffer.frameLength)
    
    // Calculate the RMS volume level
    var rms: Float = 0.0
    for i in 0..<frameCount {
        let sample = floatData[i]
        rms += sample * sample
    }
    rms = sqrt(rms / Float(frameCount))
    
    // Now, 'rms' contains the RMS volume level in real-time
    print(rms)
}

The code iterates, does the math to give RMS for small chunk of time. For smoother RMS over time, accumulate and do a moving average.