[Speex-dev] Integrating speex with VideoNet application: Constant background noise

Carine Liang carineliang at yahoo.com.sg
Mon Oct 30 21:05:49 PST 2006


I am developing a peer-to-peer video conference application which uses speex as a codec for the voice. 

I am new to speex, so please bear with me if I asked the obvious. After I added the encode and decode function to my MFC app, I heard a constant background noise, even when no one is speaking into the microphone. 

#define FRAME_SIZE 160

The application is coded in MFC C++. The record buffer is set to be the same as the FRAME_SIZE such that my callback function is called everytime 160 bytes of data is recorded.

Here's what I did in the initialisation (called only once).
m_waveFormatEx.wFormatTag =WAVE_FORMAT_PCM;
m_waveFormatEx.nChannels =1;
m_waveFormatEx.wBitsPerSample =8;
m_waveFormatEx.cbSize =0;
m_waveFormatEx.nSamplesPerSec = 8000;
m_waveFormatEx.nBlockAlign =1;
m_waveFormatEx.nAvgBytesPerSec = 8000;

int quality =8;
enc_state = speex_encoder_init(&speex_nb_mode);
speex_encoder_ctl(enc_state, SPEEX_SET_QUALITY, &quality);

In my recording callback function
LRESULT RecordSound::OnSoundData(WPARAM wParam, LPARAM lParam)
    dataPtr = (char *)lpHdr ->lpData;
    dataSize = (int)lpHdr ->dwBytesRecorded;

    for(int k=0;k<FRAME_SIZE;k++)
        input[k] = dataPtr[k];     //input is float[FRAME_SIZE]
    speex_encode(enc_state, input, &bits);
    encByte = speex_bits_write(&bits, cbits, 200);

    //send cbits to peer computer via sockets

In the receiver's initialization function, I've initialized the speex_decoder.

dec_state = speex_decoder_init(&speex_nb_mode);

In the receiver's socket function, it reads from socket and store the data in cbits (char array).
    speex_bits_read_from(&bits, cbits, retvalue); //retvalue is 38
    speex_decode(dec_state, &bits, output); //where output is float array

    for(int k=0;k<FRAME_SIZE;k++)
        out[k] = output[k];  //out is a char array

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