// open file
  fpIn := FileOpen(MP3FileName, fmOpenRead);
  if (fpIn = 0) then Exit;

  // find out how big the decompressed buffer will be
  rawbufsize := 0;
  acmStreamSize(g_mp3stream, MP3_BLOCK_SIZE, rawbufsize, ACM_STREAMSIZEF_SOURCE);

  // allocate our I/O buffers
  mp3Buf := PByte(LocalAlloc(LPTR, MP3_BLOCK_SIZE));
  rawbuf := pByte(LocalAlloc(LPTR, rawbufsize));

  // prepare the decoder
  ZeroMemory(@mp3streamHead, sizeof(TACMSTREAMHEADER));
  mp3streamHead.cbStruct := sizeof(TACMSTREAMHEADER);
  mp3streamHead.pbSrc := mp3buf;
  mp3streamHead.cbSrcLength := MP3_BLOCK_SIZE;
  mp3streamHead.pbDst := rawbuf;
  mp3streamHead.cbDstLength := rawbufsize;
  acmStreamPrepareHeader(g_mp3stream, mp3streamHead, 0);

  // let''s dump this data off to disk (for debug checking!)
  RawFileName := ChangeFileExt(MP3FileName, ''.raw'');
  fpOut := FileCreate(RawFileName);
  if (fpOut = 0) then Exit;

  FileSeek(fpIn, 0, 0);

  while True do
  begin
    //suck in some MP3 data
    Count := FileRead(fpIn, mp3buf^, MP3_BLOCK_SIZE);
    if (Count <> MP3_BLOCK_SIZE) then break;

    // convert the data
    mmr := acmStreamConvert(g_mp3stream, mp3streamHead, ACM_STREAMCONVERTF_BLOCKALIGN);
    if mmr <> 0 then
    begin
      MessageBox(0, ''输入参数错误。请检查你的输入参数。'', ''系统提示： '', 64);
      Exit;
    end;

    //write the decoded PCM to disk
    Count := FileWrite(fpOut, rawbuf^, mp3streamHead.cbDstLengthUsed);
    if Count <> mp3streamHead.cbDstLengthUsed then
    begin
      MessageBox(0, ''输入参数错误。请检查你的输入参数。'', ''系统提示： '', 64);
      Exit;
    end;
  end; ;

//  clean up after yourself like a good little boy
  FileClose(fpIn);
  FileClose(fpOut);
  acmStreamUnprepareHeader(g_mp3stream, mp3streamHead, 0);
  LocalFree(LongInt(rawbuf));
  LocalFree(LongInt(mp3buf));
  acmStreamClose(g_mp3stream, 0);
  Result := True;
end;

 ConverMP3ToRaw函数是将MP3转换成RAW(RIFF格式)，添加WAV文件头就是WAV文件了。