本次安装基于系统CentOS Linux release 6.0 (Final)

1.下载源码

ftp下载地址: ftp://ftp.mars.org/pub/mpeg/

2.解压源码

$ tar zxvf libmad-0.15.0b.tar.gz

3.编译前配置

$ cd libmad-0.15.0b
$ ./configure --prefix=$HOME/local/prior

4.编译源码

$ make

出现错误

gcc -DHAVE_CONFIG_H -I. -I. -I. -DFPM_INTEL -DASO_ZEROCHECK -Wall -march=i486 -g -O -fforce-mem -fforce-addr -fthread-jumps -fcse-follow-jumps -fcse-skip-blocks -fexpensive-optimizations -fregmove -fschedule-insns2 -fstrength-reduce -MT version.lo -MD -MP -MF .deps/version.Tpo -c version.c  -fPIC -DPIC -o .libs/version.lo
cc1: error: unrecognized command line option "-fforce-mem"
make[2]: *** [version.lo] Error 1
make[2]: Leaving directory `/home/mad/downloads/libmad-0.15.0b'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/mad/downloads/libmad-0.15.0b'
make: *** [all] Error 2

5.重新编译

打开Makefile，找到-fforce-mem并删除

$ make

6.安装libmad

$ make install

7.修改minimad.c

添加全局变量

FILE *pcm_fp;

修改output函数

enum mad_flow output(void *data,
                     struct mad_header const *header,
                     struct mad_pcm *pcm)
{
  unsigned int nchannels, nsamples;
  mad_fixed_t const *left_ch, *right_ch;
  char tmpchar;

  /* pcm->samplerate contains the sampling frequency */

  nchannels = pcm->channels;
  nsamples  = pcm->length;
  left_ch   = pcm->samples[0];
  right_ch  = pcm->samples[1];

  while (nsamples--) {
    signed int sample;

    /* output sample(s) in 16-bit signed little-endian PCM */

    sample = scale(*left_ch++);
    tmpchar = ((sample >> 0) & 0xff);
    fwrite(&tmpchar, 1, 1, pcm_fp);
    tmpchar = ((sample >> 8) & 0xff);
    fwrite(&tmpchar, 1, 1, pcm_fp);
    //putchar((sample >> 0) & 0xff);
    //putchar((sample >> 8) & 0xff);

    if (nchannels == 2) {
      sample = scale(*right_ch++);
      tmpchar = ((sample >> 0) & 0xff);
      fwrite(&tmpchar, 1, 1, pcm_fp);
      tmpchar = ((sample >> 8) & 0xff);
      fwrite(&tmpchar, 1, 1, pcm_fp);
      //putchar((sample >> 0) & 0xff);
      //putchar((sample >> 8) & 0xff);
    }
  }

  return MAD_FLOW_CONTINUE;
}

修改主函数

int main(int argc, char *argv[])
{
  struct stat stat;
  char file[2][256];
  void *fdm;
  int fd;

  if (argc != 3)
    return 1;

  memset(file, 0x00, sizeof(file));

  strncpy(file[0], argv[1], 255);
  strncpy(file[1], argv[2], 255);
  printf("%s\n", file[0]);

  pcm_fp = fopen(file[1], "wb");

  fd = open(file[0], O_RDONLY);

  if (fstat(fd, &stat) == -1 ||
      stat.st_size == 0)
    return 2;

  fdm = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, fd, 0);
  if (fdm == MAP_FAILED)
    return 3;

  printf("decode begin\n");

  decode(fdm, stat.st_size);

  printf("decode end\n");

  if (munmap(fdm, stat.st_size) == -1)
    return 4;

  fclose(pcm_fp);

  return 0;
}

编译minimad

$ gcc -o minimad minimad.c -L$HOME/local/prior/lib -lmad

8.测试运行

$ ./minimad 3.mp3 3.pcm

成功生成解码后的3.pcm文件, 下面报错属正常现象

decoding error 0x0101 (lost synchronization) at byte offset 0
decoding error 0x0101 (lost synchronization) at byte offset 3548123

用Audacity能正常播放