Speex 一个开源的声学回声消除器(Acoustic Echo Cancellation)



    
        
            
            Hi,
            I am using the speex 1.0.4 library from Windows.
            I have posted my problem before but didn't get a solution. I am doing an
            VOIP project
            in which i am recording sound and streaming it to the peer. I wanted to
            encode and decode
            wav files that brought me to this site.
            I am recording sound in the following format:-
            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;
            The recording is as follows :-
            When the buffer(size = 2000 bytes) gets filled with sound data a
            function with the body shown
            below is called.
            LPWAVEHDR lpHdr = (LPWAVEHDR) lParam;
            if(lpHdr->dwBytesRecorded==0 || lpHdr==NULL)
            return ERROR_SUCCESS;
            ::waveInUnprepareHeader(m_hRecord, lpHdr, sizeof(WAVEHDR));
            Here lpHdr->lpData contains the audio data in a character array.
            Now here I want to use Speex codec for encoding the data so the encoding
            function is
            called (I am thankful to Tay YueWeng for the function).
            char *encode(char *buffer, int &encodeSize)
            {
            char   *encodedBuffer = new char[RECBUFFER/2];            /*
            RECBUFFER = 2000 */
            short   speexShort;
            float  speexFloat[RECBUFFER/2];
            void   *mEncode       = speex_encoder_init(&speex_nb_mode);
            /*Initialization of the structure that holds the bits*/
            speex_bits_init(&mBits);
            // Convert the audio to a short then to a float buffer
            int    halfBufferSize = RECBUFFER/2;
            for (int i = 0; i < halfBufferSize; i++)
            {
            memcpy(&speexShort, &buffer[i*2], sizeof(short));
            speexFloat[i]     = speexShort;
            }
            // Encode the sound data using the float buffer
            speex_bits_reset(&mBits);
            speex_encode(mEncode, speexFloat, &mBits);
            encodeSize            = speex_bits_write(&mBits, encodedBuffer,
            RECBUFFER/2);
            /*Destroy the encoder state*/
            speex_encoder_destroy(mEncode);
            /*Destroy the bit-stream struct*/
            speex_bits_destroy(&mBits);
            // Return the encoded buffer
            return encodedBuffer;
            }
            Here i noticed that though my captured audio data is 2000 bytes the
            compressed form is
            always 38 bytes. In the speexFloat array above i get values in the range
            -32767 to +32767.
            Is it correct. Also after calling the 'speex_encode' function the first
            160 values in the
            input float array i.e. speexFloat is changed (why does it happen?Is
            anything abnormal).
            Further after calling the above function for testing I decode the
            returned encoded data
            immediately by calling the decoding function shown bellow :-
            char *decode (char *buffer, int encodeSize)
            {
            char *decodedBuffer   = new char[RECBUFFER];
            short speexShort;
            float speexFloat[RECBUFFER/2];
            // Decode the sound data into a float buffer
            void  *mDecode        = speex_decoder_init(&speex_nb_mode);
            /*Initialization of the structure that holds the bits*/
            speex_bits_init(&mBits);
            int    halfBufferSize = RECBUFFER/2;
            speex_bits_reset(&mBits);
            speex_bits_read_from(&mBits, buffer, encodeSize);
            speex_decode(mDecode, &mBits, speexFloat);
            // Convert from float to short to char
            for (int i = 0; i < halfBufferSize; i++)
            {
            speexShort = speexFloat[i];
            memcpy(&decodedBuffer[i*2], &speexShort, sizeof(short));
            }
            /*Destroy the decoder state*/
            speex_encoder_destroy(mDecode);
            /*Destroy the bit-stream truct*/
            speex_bits_destroy(&mBits);
            // Return the buffer
            return decodedBuffer;
            }
            After decoding using the above function only the first 160 values in the
            decodedBuffer array is
            changed. i.e i encoded an 2000 byte audio data to get a 38 byte encoded
            audio data. On decoding
            the 38 byte audio data i get an decompressed 160 byte data. I don't
            understand whats going
            wrong. I checked all the messages posted in this newsgroup and did'nt
            find an answer so i am
            posting this code hoping that it gets solved soon.  Thanks in advance.

Subject:	Encoding and decoding problem in speex 1.0.4
List-id:	speex-dev.xiph.org

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Encoding and decoding problem in speex 1.0.4