关于AVI文件合成时候音频编码的问题

自己写了一个AVI文件合成工具，用于生成AVI在电视中播放，支持视频编码为Xvid,音频编码为MP3，我利用的是vfw进行编程，现在问题是音频流无法加入，只能加入WAV编码的音频，导致在电视上只有图像没有声音，在电脑上视频音频正常，请问怎么加MP3编码的音频到AVI文件中，，，，刚接触视频，高手告诉怎么改 就行了
代码如下：
HRESULT CCREAT::AddAviWav(HAVI avi, const char *src, DWORD flags)
{
if (avi==NULL)
return AVIERR_BADHANDLE;
if (flags!=SND_MEMORY && flags!=SND_FILENAME)
return AVIERR_BADFLAGS;
if (src==0)
return AVIERR_BADPARAM;
TAviUtil *au = (TAviUtil*)avi;
if (au->iserr)
return AVIERR_ERROR;
//
char *buf=0; WavChunk *wav = (WavChunk*)src;
if (flags==SND_FILENAME)
{
HANDLE hf=CreateFile(src,GENERIC_READ,FILE_SHARE_READ,NULL,OPEN_EXISTING,0,NULL);
if (hf==INVALID_HANDLE_VALUE)
{
au->iserr=true;
return AVIERR_FILEOPEN;
}
DWORD size = GetFileSize(hf,NULL);
buf = new char[size];
DWORD red;
ReadFile(hf,buf,size,&red,NULL);
CloseHandle(hf);
wav = (WavChunk*)buf;
}
//
// check that format doesn't clash
bool badformat=false;
if (au->wfx.nChannels==0)
{
au->wfx.wFormatTag=wav->fmt.wFormatTag;
au->wfx.cbSize=0;
au->wfx.nAvgBytesPerSec=wav->fmt.dwAvgBytesPerSec;
au->wfx.nBlockAlign=wav->fmt.wBlockAlign;
au->wfx.nChannels=wav->fmt.wChannels;
au->wfx.nSamplesPerSec=wav->fmt.dwSamplesPerSec;
au->wfx.wBitsPerSample=wav->fmt.wBitsPerSample;
}
else
{
if (au->wfx.wFormatTag!=wav->fmt.wFormatTag) badformat=true;
if (au->wfx.nAvgBytesPerSec!=wav->fmt.dwAvgBytesPerSec) badformat=true;
if (au->wfx.nBlockAlign!=wav->fmt.wBlockAlign) badformat=true;
if (au->wfx.nChannels!=wav->fmt.wChannels) badformat=true;
if (au->wfx.nSamplesPerSec!=wav->fmt.dwSamplesPerSec) badformat=true;
if (au->wfx.wBitsPerSample!=wav->fmt.wBitsPerSample) badformat=true;
}
if (badformat)
{
if (buf!=0)
delete[] buf;
return AVIERR_BADFORMAT;
}
//
if (au->as==0) // create the stream if necessary
{
AVISTREAMINFO ahdr;
ZeroMemory(&ahdr,sizeof(ahdr));
ahdr.fccType=streamtypeAUDIO;
ahdr.dwScale=au->wfx.nBlockAlign;
ahdr.dwRate=au->wfx.nSamplesPerSec*au->wfx.nBlockAlign;
ahdr.dwSampleSize=au->wfx.nBlockAlign;
ahdr.dwQuality=(DWORD)-1;
HRESULT hr = AVIFileCreateStream(au->pfile, &au->as, &ahdr);
if (hr!=AVIERR_OK)
{
if (buf!=0) delete[] buf;
au->iserr=true;
return hr;
}
hr = AVIStreamSetFormat(au->as,0,&au->wfx,sizeof(WAVEFORMATEX));
if (hr!=AVIERR_OK)
{
if (buf!=0)
delete[] buf;
au->iserr=true;
return hr;
}
}
//
// now we can write the data
unsigned long numbytes = wav->dat.size;
unsigned long numsamps = numbytes*8 / au->wfx.wBitsPerSample;
HRESULT hr = AVIStreamWrite(au->as,au->nsamp,numsamps,wav->dat.data,numbytes,0,NULL,NULL);
if (buf!=0)
delete[] buf;
if (hr!=AVIERR_OK)
{
au->iserr=true;
return hr;
}
au->nsamp+=numsamps;
return S_OK;
}