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

前段时间，搞了一阵声学回声消除，非常郁闷，因为没有成功，但可以说学到一点东西吧，至少理论上懂了一点。
为什么需要声学回声消除呢？在一般的VOIP软件或视频会议系统中，假设我们只有A和B两个人在通话，首先，A的声音传给B，B然后用喇叭放出来，而这时B的MIC呢则会采集到喇叭放出来的声音，然后传回给A，如果这个传输的过程中时延足够大，A就会听到一个和自己刚才说过的话一样的声音，这就是回声，声学回声消除器的作用就是在B端对B采集到的声音进行处理，把采集到声音包含的A的声音去掉再传给A，这样，A就不会听到自己说过的话了。
声学回声消除的原理我就不说了，这在网上有很多文档，网上缺少的是实现，所以，我在这把一个开源的声学回声消除器介绍一下，希望对有些有人用，如果有人知道怎么把这消除器用的基于实时流的VOIP软件中，希望能一起分享一下。
这个声学回声消除器是一个著名的音频编解码器speex中的一部分，1.1.9版本后的回声消除器才起作用，以前版本的都不行，我用的也是这个版本，测试表明，用同一个模拟文件，它有效果比INTEL IPP库4.1版中的声学回声消除器的还要好。
先说编译。首先，从www.speex.org上下载speex1.1.9的源代码，解压，打开speex\win32\libspeex中的libspeex.dsw，这个工作区里有两个工程，一个是libspeex，另一个是libspeex_dynamic。然后，将libspeex中的mdf.c文件添加到工程libspeex中，编译即可。
以下是我根据文档封装的一个类，里面有一个测试程序： //file name: speexEC.h
#ifndef SPEEX_EC_H
#define SPEEX_EC_H
#include <stdio.h>
#include <stdlib.h>
#include "speex/speex_echo.h"
#include "speex/speex_preprocess.h"
class CSpeexEC
{
public:
CSpeexEC();
~CSpeexEC();
void Init(int frame_size=160, int filter_length=1280, int sampling_rate=8000);
void DoAEC(short *mic, short *ref, short *out);

protected:
void Reset();

private:
bool m_bHasInit;
SpeexEchoState* m_pState;
SpeexPreprocessState* m_pPreprocessorState;
int m_nFrameSize;
int m_nFilterLen;
int m_nSampleRate;
float* m_pfNoise;
};

#endif

//fine name:speexEC.cpp
#include "SpeexEC.h"

CSpeexEC::CSpeexEC()
{
m_bHasInit = false;
m_pState = NULL;
m_pPreprocessorState = NULL;
m_nFrameSize = 160;
m_nFilterLen = 160*8;
m_nSampleRate = 8000;
m_pfNoise = NULL;
}

CSpeexEC::~CSpeexEC()
{
Reset();
}

void CSpeexEC::Init(int frame_size, int filter_length, int sampling_rate)
{
Reset();

if (frame_size<=0 || filter_length<=0 || sampling_rate<=0)
{
m_nFrameSize =160;
m_nFilterLen = 160*8;
m_nSampleRate = 8000;
}
else
{
m_nFrameSize =frame_size;
m_nFilterLen = filter_length;
m_nSampleRate = sampling_rate;
}

m_pState = speex_echo_state_init(m_nFrameSize, m_nFilterLen);
m_pPreprocessorState = speex_preprocess_state_init(m_nFrameSize, m_nSampleRate);
m_pfNoise = new float[m_nFrameSize+1];
m_bHasInit = true;
}

void CSpeexEC::Reset()
{
if (m_pState != NULL)
{
speex_echo_state_destroy(m_pState);
m_pState = NULL;
}
if (m_pPreprocessorState != NULL)
{
speex_preprocess_state_destroy(m_pPreprocessorState);
m_pPreprocessorState = NULL;
}
if (m_pfNoise != NULL)
{
delete []m_pfNoise;
m_pfNoise = NULL;
}
m_bHasInit = false;
}

void CSpeexEC:DoAEC(short* mic, short* ref, short* out)
{
if (!m_bHasInit)
return;

speex_echo_cancel(m_pState, mic, ref, out, m_pfNoise);
speex_preprocess(m_pPreprocessorState, (__int16 *)out, m_pfNoise);

}

可以看出，这个回声消除器类很简单，只要初始化一下就可以调用了。但是，要注意的是，传给回声消除器的两个声音信号，必须同步得非常的好，就是说，在B端，接收到A说的话以后，要把这些话音数据传给回声消除器做参考，然后再传给声卡，声卡再放出来，这有一段延时，这时，B再采集，然后传给回声消除器，与那个参考数据比较，从采集到的数据中把频域和参考数据相同的部分消除掉。如果传给消除器的两个信号同步得不好，即两个信号找不到频域相同的部分，就没有办法进行消除了。
测试程序：

#define NN 160
void main()
{
FILE* ref_fd, *mic_fd, *out_fd;
short ref[NN], mic[NN], out[NN];
ref_fd = fopen ("ref.pcm", "rb");　//打开参考文件，即要消除的声音
mic_fd = fopen ("mic.pcm", "rb");//打开mic采集到的声音文件，包含回声在里面
out_fd = fopen ("echo.pcm", "wb");//消除了回声以后的文件

CSpeexEC ec;
ec.Init();

while (fread(mic, 1, NN*2, mic_fd))
{
fread(ref, 1, NN*2, ref_fd);
ec.DoAEC(mic, ref, out);
fwrite(out, 1, NN*2, out_fd);
}

fclose(ref_fd);
fclose(mic_fd);
fclose(out_fd);
}

　　以上的程序是用文件来模拟回声和MIC，但在实时流中是大不一样的，在一般的VOIP软件中，接收对方的声音并传到声卡中播放是在一个线程中进行的，而采集本地的声音并传送到对方又是在另一个线程中进行的，而声学回声消除器在对采集到的声音进行回声消除的同时，还需要播放线程中的数据作为参考，而要同步这两个线程中的数据是非常困难的，因为稍稍有些不同步，声学回声消除器中的自适应滤波器就会发散，不但消除不了回声，还会破坏原始采集到的声音，使被破坏的声音难以分辨。我做过好多尝试，始终无法用软件来实现对这两个线程中的数据进行同步，导致实现失败，希望有经验的网友们一起分享一下这方面的经验。

示例代码：

Sample code

This section shows sample code for encoding and decoding speech using the Speex API. The commands can be used to encode and decode a file by calling:
% sampleenc in_file.sw | sampledec out_file.sw
where both files are raw (no header) files encoded at 16 bits per sample (in the machine natural endianness).

sampleenc.c

sampleenc takes a raw 16 bits/sample file, encodes it and outputs a Speex stream to stdout. Note that the packing used is NOT compatible with that of speexenc/speexdec.

#include <speex/speex.h>
#include <stdio.h>
/*The frame size in hardcoded for this sample code but it doesn't have to be*/
#define FRAME_SIZE 160
int main(int argc, char **argv)
{
char *inFile;
FILE *fin;
short in[FRAME_SIZE];
float input[FRAME_SIZE];
char cbits[200];
int nbBytes;
/*Holds the state of the encoder*/
void *state;
/*Holds bits so they can be read and written to by the Speex routines*/
SpeexBits bits;
int i, tmp;
/*Create a new encoder state in narrowband mode*/
state = speex_encoder_init(&speex_nb_mode);
/*Set the quality to 8 (15 kbps)*/
tmp=8;
speex_encoder_ctl(state, SPEEX_SET_QUALITY, &tmp);
inFile = argv[1];
fin = fopen(inFile, "r");
/*Initialization of the structure that holds the bits*/
speex_bits_init(&bits);
while (1)
{
/*Read a 16 bits/sample audio frame*/
fread(in, sizeof(short), FRAME_SIZE, fin);
if (feof(fin))
break;
/*Copy the 16 bits values to float so Speex can work on them*/
for (i=0;i<FRAME_SIZE;i++)
input[i]=in[i];
/*Flush all the bits in the struct so we can encode a new frame*/
speex_bits_reset(&bits);
/*Encode the frame*/
speex_encode(state, input, &bits);
/*Copy the bits to an array of char that can be written*/
nbBytes = speex_bits_write(&bits, cbits, 200);
/*Write the size of the frame first. This is what sampledec expects but
it's likely to be different in your own application*/
fwrite(&nbBytes, sizeof(int), 1, stdout);
/*Write the compressed data*/
fwrite(cbits, 1, nbBytes, stdout);
}
/*Destroy the encoder state*/
speex_encoder_destroy(state);
/*Destroy the bit-packing struct*/
speex_bits_destroy(&bits);
fclose(fin);
return 0;
}

sampledec.c

sampledec reads a Speex stream from stdin, decodes it and outputs it to a raw 16 bits/sample file. Note that the packing used is NOT compatible with that of speexenc/speexdec.

#include <speex/speex.h>
#include <stdio.h>
/*The frame size in hardcoded for this sample code but it doesn't have to be*/
#define FRAME_SIZE 160
int main(int argc, char **argv)
{
char *outFile;
FILE *fout;
/*Holds the audio that will be written to file (16 bits per sample)*/
short out[FRAME_SIZE];
/*Speex handle samples as float, so we need an array of floats*/
float output[FRAME_SIZE];
char cbits[200];
int nbBytes;
/*Holds the state of the decoder*/
void *state;
/*Holds bits so they can be read and written to by the Speex routines*/
SpeexBits bits;
int i, tmp;
/*Create a new decoder state in narrowband mode*/
state = speex_decoder_init(&speex_nb_mode);
/*Set the perceptual enhancement on*/
tmp=1;
speex_decoder_ctl(state, SPEEX_SET_ENH, &tmp);
outFile = argv[1];
fout = fopen(outFile, "w");
/*Initialization of the structure that holds the bits*/
speex_bits_init(&bits);
while (1)
{
/*Read the size encoded by sampleenc, this part will likely be
different in your application*/
fread(&nbBytes, sizeof(int), 1, stdin);
fprintf (stderr, "nbBytes: %d\n", nbBytes);
if (feof(stdin))
break;
/*Read the "packet" encoded by sampleenc*/
fread(cbits, 1, nbBytes, stdin);
/*Copy the data into the bit-stream struct*/
speex_bits_read_from(&bits, cbits, nbBytes);
/*Decode the data*/
speex_decode(state, &bits, output);
/*Copy from float to short (16 bits) for output*/
for (i=0;i<FRAME_SIZE;i++)
out[i]=output[i];
/*Write the decoded audio to file*/
fwrite(out, sizeof(short), FRAME_SIZE, fout);
}
/*Destroy the decoder state*/
speex_decoder_destroy(state);
/*Destroy the bit-stream truct*/
speex_bits_destroy(&bits);
fclose(fout);
return 0;
}

开源 H323 协议中封装的使用参考代码：


/*
* speexcodec.cxx
*
* Speex codec handler
*
* Open H323 Library
*
* Copyright (c) 2002 Equivalence Pty. Ltd.
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/ *
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is Open H323 Library.
*
* The Initial Developer of the Original Code is Equivalence Pty. Ltd.
*
* Contributor(s): ______________________________________.
*
* $Log: speexcodec.cxx,v $
* Revision 1.20 2002/12/08 22:59:41 rogerh
* Add XiphSpeex codec. Not yet finished.
*
* Revision 1.19 2002/12/06 10:11:54 rogerh
* Back out the Xiph Speex changes on a tempoary basis while the Speex
* spec is being redrafted.
*
* Revision 1.18 2002/12/06 03:27:47 robertj
* Fixed MSVC warnings
*
* Revision 1.17 2002/12/05 12:57:17 rogerh
* Speex now uses the manufacturer ID assigned to Xiph.Org.
* To support existing applications using Speex, applications can use the
* EquivalenceSpeex capabilities.
*
* Revision 1.16 2002/11/25 10:24:50 craigs
* Fixed problem with Speex codec names causing mismatched capabilities
* Reported by Ben Lear
*
* Revision 1.15 2002/11/09 07:08:20 robertj
* Hide speex library from OPenH323 library users.
* Made public the media format names.
* Other cosmetic changes.
*
* Revision 1.14 2002/10/24 05:33:19 robertj
* MSVC compatibility
*
* Revision 1.13 2002/10/22 11:54:32 rogerh
* Fix including of speex.h
*
* Revision 1.12 2002/10/22 11:33:04 rogerh
* Use the local speex.h header file
*
* Revision 1.11 2002/10/09 10:55:21 rogerh
* Update the bit rates to match what the codec now does
*
* Revision 1.10 2002/09/02 21:58:40 rogerh
* Update for Speex 0.8.0
*
* Revision 1.9 2002/08/21 06:49:13 rogerh
* Fix the RTP Payload size too small problem with Speex 0.7.0.
*
* Revision 1.8 2002/08/15 18:34:51 rogerh
* Fix some more bugs
*
* Revision 1.7 2002/08/14 19:06:53 rogerh
* Fix some bugs when using the speex library
*
* Revision 1.6 2002/08/14 04:35:33 craigs
* CHanged Speex names to remove spaces
*
* Revision 1.5 2002/08/14 04:30:14 craigs
* Added bit rates to Speex codecs
*
* Revision 1.4 2002/08/14 04:27:26 craigs
* Fixed name of Speex codecs
*
* Revision 1.3 2002/08/14 04:24:43 craigs
* Fixed ifdef problem
*
* Revision 1.2 2002/08/13 14:25:25 craigs
* Added trailing newlines to avoid Linux warnings
*
* Revision 1.1 2002/08/13 14:14:59 craigs
* Initial version
*
*/

#include <ptlib.h>

#ifdef __GNUC__
#pragma implementation "speexcodec.h"
#endif

#include "speexcodec.h"

#include "h323caps.h"
#include "h245.h"
#include "rtp.h"

extern "C" {
#include "speex/libspeex/speex.h"
};

#define new PNEW

#define XIPH_COUNTRY_CODE 0xB5 // (181) Country code for United States
#define XIPH_T35EXTENSION 0
#define XIPH_MANUFACTURER_CODE 0x0026 // Allocated by Delta Inc

#define EQUIVALENCE_COUNTRY_CODE 9 // Country code for Australia
#define EQUIVALENCE_T35EXTENSION 0
#define EQUIVALENCE_MANUFACTURER_CODE 61 // Allocated by Australian Communications Authority, Oct 2000

#define SAMPLES_PER_FRAME 160

#define SPEEX_BASE_NAME "Speex"

#define SPEEX_NARROW2_H323_NAME SPEEX_BASE_NAME "Narrow-5.95k{sw}"
#define SPEEX_NARROW3_H323_NAME SPEEX_BASE_NAME "Narrow-8k{sw}"
#define SPEEX_NARROW4_H323_NAME SPEEX_BASE_NAME "Narrow-11k{sw}"
#define SPEEX_NARROW5_H323_NAME SPEEX_BASE_NAME "Narrow-15k{sw}"
#define SPEEX_NARROW6_H323_NAME SPEEX_BASE_NAME "Narrow-18.2k{sw}"

H323_REGISTER_CAPABILITY(SpeexNarrow2AudioCapability, SPEEX_NARROW2_H323_NAME);
H323_REGISTER_CAPABILITY(SpeexNarrow3AudioCapability, SPEEX_NARROW3_H323_NAME);
H323_REGISTER_CAPABILITY(SpeexNarrow4AudioCapability, SPEEX_NARROW4_H323_NAME);
H323_REGISTER_CAPABILITY(SpeexNarrow5AudioCapability, SPEEX_NARROW5_H323_NAME);
H323_REGISTER_CAPABILITY(SpeexNarrow6AudioCapability, SPEEX_NARROW6_H323_NAME);

#define XIPH_SPEEX_NARROW2_H323_NAME SPEEX_BASE_NAME "Narrow-5.95k(Xiph){sw}"
#define XIPH_SPEEX_NARROW3_H323_NAME SPEEX_BASE_NAME "Narrow-8k(Xiph){sw}"
#define XIPH_SPEEX_NARROW4_H323_NAME SPEEX_BASE_NAME "Narrow-11k(Xiph){sw}"
#define XIPH_SPEEX_NARROW5_H323_NAME SPEEX_BASE_NAME "Narrow-15k(Xiph){sw}"
#define XIPH_SPEEX_NARROW6_H323_NAME SPEEX_BASE_NAME "Narrow-18.2k(Xiph){sw}"

H323_REGISTER_CAPABILITY(XiphSpeexNarrow2AudioCapability, XIPH_SPEEX_NARROW2_H323_NAME);
H323_REGISTER_CAPABILITY(XiphSpeexNarrow3AudioCapability, XIPH_SPEEX_NARROW3_H323_NAME);
H323_REGISTER_CAPABILITY(XiphSpeexNarrow4AudioCapability, XIPH_SPEEX_NARROW4_H323_NAME);
H323_REGISTER_CAPABILITY(XiphSpeexNarrow5AudioCapability, XIPH_SPEEX_NARROW5_H323_NAME);
H323_REGISTER_CAPABILITY(XiphSpeexNarrow6AudioCapability, XIPH_SPEEX_NARROW6_H323_NAME);

/////////////////////////////////////////////////////////////////////////

static int Speex_Bits_Per_Second(int mode) {
void *tmp_coder_state;
int bitrate;
tmp_coder_state = speex_encoder_init(&speex_nb_mode);
speex_encoder_ctl(tmp_coder_state, SPEEX_SET_QUALITY, &mode);
speex_encoder_ctl(tmp_coder_state, SPEEX_GET_BITRATE, &bitrate);
speex_encoder_destroy(tmp_coder_state);
return bitrate;
}

static int Speex_Bytes_Per_Frame(int mode) {
int bits_per_frame = Speex_Bits_Per_Second(mode) / 50; // (20ms frame size)
return ((bits_per_frame+7)/8); // round up
}

OpalMediaFormat const OpalSpeexNarrow_5k95(OPAL_SPEEX_NARROW_5k95,
OpalMediaFormat::DefaultAudioSessionID,
RTP_DataFrame::DynamicBase,
TRUE, // Needs jitter
Speex_Bits_Per_Second(2),
Speex_Bytes_Per_Frame(2),
SAMPLES_PER_FRAME, // 20 milliseconds
OpalMediaFormat::AudioTimeUnits);

OpalMediaFormat const OpalSpeexNarrow_8k(OPAL_SPEEX_NARROW_8k,
OpalMediaFormat::DefaultAudioSessionID,
RTP_DataFrame::DynamicBase,
TRUE, // Needs jitter
Speex_Bits_Per_Second(3),
Speex_Bytes_Per_Frame(3),
SAMPLES_PER_FRAME, // 20 milliseconds
OpalMediaFormat::AudioTimeUnits);

OpalMediaFormat const OpalSpeexNarrow_11k(OPAL_SPEEX_NARROW_11k,
OpalMediaFormat::DefaultAudioSessionID,
RTP_DataFrame::DynamicBase,
TRUE, // Needs jitter
Speex_Bits_Per_Second(4),
Speex_Bytes_Per_Frame(4),
SAMPLES_PER_FRAME, // 20 milliseconds
OpalMediaFormat::AudioTimeUnits);

OpalMediaFormat const OpalSpeexNarrow_15k(OPAL_SPEEX_NARROW_15k,
OpalMediaFormat::DefaultAudioSessionID,
RTP_DataFrame::DynamicBase,
TRUE, // Needs jitter
Speex_Bits_Per_Second(5),
Speex_Bytes_Per_Frame(5),
SAMPLES_PER_FRAME, // 20 milliseconds
OpalMediaFormat::AudioTimeUnits);

OpalMediaFormat const OpalSpeexNarrow_18k2(OPAL_SPEEX_NARROW_18k2,
OpalMediaFormat::DefaultAudioSessionID,
RTP_DataFrame::DynamicBase,
TRUE, // Needs jitter
Speex_Bits_Per_Second(6),
Speex_Bytes_Per_Frame(6),
SAMPLES_PER_FRAME, // 20 milliseconds
OpalMediaFormat::AudioTimeUnits);

/////////////////////////////////////////////////////////////////////////

SpeexNonStandardAudioCapability::SpeexNonStandardAudioCapability(int mode)
: H323NonStandardAudioCapability(1, 1,
EQUIVALENCE_COUNTRY_CODE,
EQUIVALENCE_T35EXTENSION,
EQUIVALENCE_MANUFACTURER_CODE,
NULL, 0, 0, P_MAX_INDEX)
{
PStringStream s;
s << "Speex bs" << speex_nb_mode.bitstream_version << " Narrow" << mode;
PINDEX len = s.GetLength();
memcpy(nonStandardData.GetPointer(len), (const char *)s, len);
}

/////////////////////////////////////////////////////////////////////////

SpeexNarrow2AudioCapability::SpeexNarrow2AudioCapability()
: SpeexNonStandardAudioCapability(2)
{
}

PObject * SpeexNarrow2AudioCapability::Clone() const
{
return new SpeexNarrow2AudioCapability(*this);
}

PString SpeexNarrow2AudioCapability::GetFormatName() const
{
return SPEEX_NARROW2_H323_NAME;
}

H323Codec * SpeexNarrow2AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_5k95, 2, direction);
}

/////////////////////////////////////////////////////////////////////////

SpeexNarrow3AudioCapability::SpeexNarrow3AudioCapability()
: SpeexNonStandardAudioCapability(3)
{
}

PObject * SpeexNarrow3AudioCapability::Clone() const
{
return new SpeexNarrow3AudioCapability(*this);
}

PString SpeexNarrow3AudioCapability::GetFormatName() const
{
return SPEEX_NARROW3_H323_NAME;
}

H323Codec * SpeexNarrow3AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_8k, 3, direction);
}

/////////////////////////////////////////////////////////////////////////

SpeexNarrow4AudioCapability::SpeexNarrow4AudioCapability()
: SpeexNonStandardAudioCapability(4)
{
}

PObject * SpeexNarrow4AudioCapability::Clone() const
{
return new SpeexNarrow4AudioCapability(*this);
}

PString SpeexNarrow4AudioCapability::GetFormatName() const
{
return SPEEX_NARROW4_H323_NAME;
}

H323Codec * SpeexNarrow4AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_11k, 4, direction);
}

/////////////////////////////////////////////////////////////////////////

SpeexNarrow5AudioCapability::SpeexNarrow5AudioCapability()
: SpeexNonStandardAudioCapability(5)
{
}

PObject * SpeexNarrow5AudioCapability::Clone() const
{
return new SpeexNarrow5AudioCapability(*this);
}

PString SpeexNarrow5AudioCapability::GetFormatName() const
{
return SPEEX_NARROW5_H323_NAME;
}

H323Codec * SpeexNarrow5AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_15k, 5, direction);
}

/////////////////////////////////////////////////////////////////////////

SpeexNarrow6AudioCapability::SpeexNarrow6AudioCapability()
: SpeexNonStandardAudioCapability(6)
{
}

PObject * SpeexNarrow6AudioCapability::Clone() const
{
return new SpeexNarrow6AudioCapability(*this);
}

PString SpeexNarrow6AudioCapability::GetFormatName() const
{
return SPEEX_NARROW6_H323_NAME;
}

H323Codec * SpeexNarrow6AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_18k2, 6, direction);
}

/////////////////////////////////////////////////////////////////////////

XiphSpeexNonStandardAudioCapability::XiphSpeexNonStandardAudioCapability(int mode)
: H323NonStandardAudioCapability(1, 1,
XIPH_COUNTRY_CODE,
XIPH_T35EXTENSION,
XIPH_MANUFACTURER_CODE,
NULL, 0, 0, P_MAX_INDEX)
{
// FIXME: To be replaced by an ASN defined block of data
PStringStream s;
s << "Speex bs" << speex_nb_mode.bitstream_version << " Narrow" << mode;
PINDEX len = s.GetLength();
memcpy(nonStandardData.GetPointer(len), (const char *)s, len);
}

/////////////////////////////////////////////////////////////////////////

XiphSpeexNarrow2AudioCapability::XiphSpeexNarrow2AudioCapability()
: XiphSpeexNonStandardAudioCapability(2)
{
}

PObject * XiphSpeexNarrow2AudioCapability::Clone() const
{
return new XiphSpeexNarrow2AudioCapability(*this);
}

PString XiphSpeexNarrow2AudioCapability::GetFormatName() const
{
return XIPH_SPEEX_NARROW2_H323_NAME;
}

H323Codec * XiphSpeexNarrow2AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_5k95, 2, direction);
}

/////////////////////////////////////////////////////////////////////////

XiphSpeexNarrow3AudioCapability::XiphSpeexNarrow3AudioCapability()
: XiphSpeexNonStandardAudioCapability(3)
{
}

PObject * XiphSpeexNarrow3AudioCapability::Clone() const
{
return new XiphSpeexNarrow3AudioCapability(*this);
}

PString XiphSpeexNarrow3AudioCapability::GetFormatName() const
{
return XIPH_SPEEX_NARROW3_H323_NAME;
}

H323Codec * XiphSpeexNarrow3AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_8k, 3, direction);
}

/////////////////////////////////////////////////////////////////////////

XiphSpeexNarrow4AudioCapability::XiphSpeexNarrow4AudioCapability()
: XiphSpeexNonStandardAudioCapability(4)
{
}

PObject * XiphSpeexNarrow4AudioCapability::Clone() const
{
return new XiphSpeexNarrow4AudioCapability(*this);
}

PString XiphSpeexNarrow4AudioCapability::GetFormatName() const
{
return XIPH_SPEEX_NARROW4_H323_NAME;
}

H323Codec * XiphSpeexNarrow4AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_11k, 4, direction);
}

/////////////////////////////////////////////////////////////////////////

XiphSpeexNarrow5AudioCapability::XiphSpeexNarrow5AudioCapability()
: XiphSpeexNonStandardAudioCapability(5)
{
}

PObject * XiphSpeexNarrow5AudioCapability::Clone() const
{
return new XiphSpeexNarrow5AudioCapability(*this);
}

PString XiphSpeexNarrow5AudioCapability::GetFormatName() const
{
return XIPH_SPEEX_NARROW5_H323_NAME;
}

H323Codec * XiphSpeexNarrow5AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_15k, 5, direction);
}

/////////////////////////////////////////////////////////////////////////

XiphSpeexNarrow6AudioCapability::XiphSpeexNarrow6AudioCapability()
: XiphSpeexNonStandardAudioCapability(6)
{
}

PObject * XiphSpeexNarrow6AudioCapability::Clone() const
{
return new XiphSpeexNarrow6AudioCapability(*this);
}

PString XiphSpeexNarrow6AudioCapability::GetFormatName() const
{
return XIPH_SPEEX_NARROW6_H323_NAME;
}

H323Codec * XiphSpeexNarrow6AudioCapability::CreateCodec(H323Codec::Direction direction) const
{
return new SpeexCodec(OpalSpeexNarrow_18k2, 6, direction);
}

/////////////////////////////////////////////////////////////////////////////

const float MaxSampleValue = 32767.0;
const float MinSampleValue = -32767.0;

SpeexCodec::SpeexCodec(const char * name, int mode, Direction dir)
: H323FramedAudioCodec(name, dir)
{
PTRACE(3, "Codec\tSpeex mode " << mode << " " << (dir == Encoder ? "en" : "de")
<< "coder created");

bits = new SpeexBits;
speex_bits_init(bits);

if (direction == Encoder) {
coder_state = speex_encoder_init(&speex_nb_mode);
speex_encoder_ctl(coder_state, SPEEX_GET_FRAME_SIZE, &encoder_frame_size);
speex_encoder_ctl(coder_state, SPEEX_SET_QUALITY, &mode);
} else {
coder_state = speex_decoder_init(&speex_nb_mode);
}
}

SpeexCodec::~SpeexCodec()
{
speex_bits_destroy(bits);
delete bits;

if (direction == Encoder)
speex_encoder_destroy(coder_state);
else
speex_decoder_destroy(coder_state);
}

BOOL SpeexCodec::EncodeFrame(BYTE * buffer, unsigned & length)
{
// convert PCM to float
float floatData[SAMPLES_PER_FRAME];
PINDEX i;
for (i = 0; i < SAMPLES_PER_FRAME; i++)
floatData[i] = sampleBuffer[i];

// encode PCM data in sampleBuffer to buffer
speex_bits_reset(bits);
speex_encode(coder_state, floatData, bits);

length = speex_bits_write(bits, (char *)buffer, encoder_frame_size);

return TRUE;
}

BOOL SpeexCodec::DecodeFrame(const BYTE * buffer, unsigned length, unsigned &)
{
float floatData[SAMPLES_PER_FRAME];

// decode Speex data to floats
speex_bits_read_from(bits, (char *)buffer, length);
speex_decode(coder_state, bits, floatData);

// convert float to PCM
PINDEX i;
for (i = 0; i < SAMPLES_PER_FRAME; i++) {
float sample = floatData[i];
if (sample < MinSampleValue)
sample = MinSampleValue;
else if (sample > MaxSampleValue)
sample = MaxSampleValue;
sampleBuffer[i] = (short)sample;
}

return TRUE;
}

VC++ 中使用 API的 char 单字节压缩代码示例：

Encoding and decoding problem in speex 1.0.4

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

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.