n the apple sample code "SpeakHere" you can do some thing like this:

AudioQueueNewInput(

&mRecordFormat,

MyInputBufferHandler,

this /* userData */,

NULL /* run loop */,

NULL /* run loop mode */,

0 /* flags */, &mQueue)

you can do some thing in function "MyInputBufferHandler" like

[self encoder:(short *)buffer->mAudioData count:buffer->mAudioDataByteSize/sizeof(short)];

the encoder function like:

while ( count >= samplesPerFrame )

{

speex_bits_reset( &bits );

speex_encode_int( enc_state, samples, &bits );

static const unsigned maxSize = 256;

char data[maxSize];

unsigned size = (unsigned)speex_bits_write( &bits, data, maxSize );

/*

do some thing... for example :send to server

*/

samples += samplesPerFrame;

count -= samplesPerFrame;

}

This is the general idea.Of course fact is hard, but you can see some open source of VOIP, maybe can help you. good luck.

Below is the Code For Capturing Audio using audioqueue and encode (wide-band) using speex (For Better Quality of Audio You can encode data in separate Thread , Change your sample size according to your capture format).

Audio format

    mSampleRate = 16000;
    mFormatID = kAudioFormatLinearPCM;
    mFramesPerPacket = 1;
    mChannelsPerFrame = 1;
    mBytesPerFrame = 2;
    mBytesPerPacket = 2;
    mBitsPerChannel = 16;
    mReserved = 0;
    mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked; 

Capture callback

    void CAudioCapturer::AudioInputCallback(void *inUserData, 
                           AudioQueueRef inAQ, 
                           AudioQueueBufferRef inBuffer, 
                           const AudioTimeStamp *inStartTime, 
                           UInt32 inNumberPacketDescriptions, 
                           const AudioStreamPacketDescription *inPacketDescs)
    {
    CAudioCapturer *This = (CMacAudioCapturer *)inUserData;

int len = 640;
char data[640];
char *pSrc = (char *)inBuffer->mAudioData;

while (len <= inBuffer->mAudioDataByteSize) 
{
    memcpy(data,pSrc,640);
    int enclen = encode(buffer,encBuffer);
    len=len+640;

    pSrc+=640; // 640 is the frame size for WB in speex (320 short)
}

AudioQueueEnqueueBuffer(This->m_audioQueue, inBuffer, 0, NULL);
    }

speex encoder

    int encode(char *buffer,char *pDest)
    {
int nbBytes=0;
speex_bits_reset(&encbits);

speex_encode_int(encstate, (short*)(buffer)  , &encbits);

nbBytes = speex_bits_write(&encbits, pDest ,640/(sizeof(short))); 

return nbBytes;
    }