LWJGL Forum

from https://www.openal.org/documentation/OpenAL_Programmers_Guide.pdf
void alcCaptureSamples(
ALCdevice *device,
ALCvoid *buffer,
ALCsizei samples
);

AL11.alcCaptureSamples(long device, java.nio.ByteBuffer buffer) isn't filling the buffer at all. Maybe its using 0 as an argument for samples?

  static long micDevice;
  static ByteBuffer captureBuffer = BufferUtils.createByteBuffer(8192);
  static boolean capturing = false;
  static void captureStart(){
if(!capturing){
  capturing = true;
  micDevice = alcCaptureOpenDevice((ByteBuffer)null,44100,AL_FORMAT_MONO16,8192);
  alcCaptureStart(micDevice);
}
  }
  static void captureSamples(){//called repeatedly
if(capturing){///test
  System.out.println(alcGetInteger(micDevice,ALC_CAPTURE_SAMPLES));// retrieve the number of samples currently available
  alcCaptureSamples(micDevice,captureBuffer);
  System.out.println(captureBuffer.mark());
  captureBuffer.flip();
}
  }
  static void captureEnd(){
if(capturing){
  capturing = false;
  alcCaptureCloseDevice(micDevice);
}
  }

Quote8189
java.nio.DirectByteBuffer[pos=0 lim=0 cap=8192]
8189
java.nio.DirectByteBuffer[pos=0 lim=0 cap=8192]
8189
java.nio.DirectByteBuffer[pos=0 lim=0 cap=8192]
8189
java.nio.DirectByteBuffer[pos=0 lim=0 cap=8192]
8189
java.nio.DirectByteBuffer[pos=0 lim=0 cap=8192]

After looking into the source code I discovered it uses buffer.remaining() for the number of samples parameter!
Here is the working code that fills the buffer.
  static long micDevice;
  static ByteBuffer captureBuffer = BufferUtils.createByteBuffer(8192);
  static boolean capturing = false;
  static void captureStart(){
if(!capturing){
  capturing = true;
  micDevice = alcCaptureOpenDevice((ByteBuffer)null,44100,AL_FORMAT_MONO16,8192);
  alcCaptureStart(micDevice);
}
  }
  static void captureSamples(){//called repeatedly
if(capturing){///test
  int numSamples = alcGetInteger(micDevice,ALC_CAPTURE_SAMPLES);
  captureBuffer.limit(numSamples);//!! you have to do this
  alcCaptureSamples(micDevice,captureBuffer);
for(int i = 0; i < numSamples;i++)System.out.println(captureBuffer.get());////test
  captureBuffer.clear();
}
  }
  static void captureEnd(){
if(capturing){
  capturing = false;
  alcCaptureCloseDevice(micDevice);
}
  }

It uses limit() to set the remaining for the buffer.

If anybody is reading this an error in the code is that each sample is 2 bytes not 1 byte.