IOS Swift read PCM Buffer

问题:

I have a project for Android reading a short[] array with PCM data from microphone Buffer for live analysis. I need to convert this functionality to iOS Swift. In Android it is very simple and looks like this..

import android.media.AudioFormat;
import android.media.AudioRecord;
...
AudioRecord recorder = new AudioRecord(MediaRecorder.AudioSource.DEFAULT, someSampleRate, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, AudioRecord.getMinBufferSize(...));
recorder.startRecording();

later I read the buffer with

recorder.read(data, offset, length); //data is short[]

(That's what i'm looking for)

Documentation: https://developer.android.com/reference/android/media/AudioRecord.html

I'm very new to Swift and iOS. I've read a lot of documentation about AudioToolkit, ...Core and whatever. All I found is C++/Obj-C and Bridging Swift Header solutions. Thats much to advanced and outdated for me.

For now I can read PCM-Data to a CAF-File with AVFoundation

settings = [
        AVLinearPCMBitDepthKey: 16 as NSNumber,
        AVFormatIDKey: Int(kAudioFormatLinearPCM),
        AVLinearPCMIsBigEndianKey: 0 as NSNumber,
        AVLinearPCMIsFloatKey: 0 as NSNumber,
        AVSampleRateKey: 12000.0,
        AVNumberOfChannelsKey: 1 as NSNumber,
        ]
...
recorder = try AVAudioRecorder(URL: someURL, settings: settings)
recorder.delegate = self
recorder.record()

But that's not what I'm looking for (or?). Is there an elegant way to achieve the android read functionality described above? I need to get a sample-array from the microphone buffer. Or do i need to do the reading on the recorded CAF file?

Thanks a lot! Please help me with easy explanations or code examples. iOS terminology is not mine yet ;-)

回答1:

If you don't mind floating point samples and 48kHz, you can quickly get audio data from the microphone like so:

let engine = AVAudioEngine()    // instance variable

func setup() {        
    let input = engine.inputNode!
    let bus = 0

    input.installTapOnBus(bus, bufferSize: 512, format: input.inputFormatForBus(bus)) { (buffer, time) -> Void in
        let samples = buffer.floatChannelData[0]
        // audio callback, samples in samples[0]...samples[buffer.frameLength-1]
    }

    try! engine.start()
}