装上fedora12后发现没有/dev/dsp了，所以用ALSA把这个程序重写了下。   程序说明：其实本来应该是在output函数中设置采样率和声道数的，但有莫名奇妙的问题。 所以定了个一般化的 #define SAMPLE_RATE 44100
#define CHANNELS 2
#define PCM_DEVICE "plughw:0,0" 即：mp3的采样率为44100Hz，声道数为2（立体声）   源代码： /* * 本程序是从 minimad 改进而来，如要更详细的说明请参看 minimad.c * * MyMinimad.c , 2009/12/25 , SiChuan University , China * * 编译： gcc MyMinimad.c -o MyMinimad -lmad -lasound * 运行： ./MyMinimad filename.mp3 */ #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/stat.h> #include <sys/mman.h> #include <sys/soundcard.h> #include <sys/ioctl.h> #include <sys/fcntl.h> #include <sys/types.h> #include <mad.h> #include <alsa/asoundlib.h> #define SAMPLE_RATE 44100 #define CHANNELS 2 #define PCM_DEVICE "plughw:0,0" static snd_pcm_hw_params_t *hwparams = NULL; static snd_pcm_t *pcm_handle = NULL; struct buffer { unsigned char const *start; unsigned long length; }; static int decode (unsigned char const *, unsigned long); static int init_alsa (); int main (int argc, char *argv[]) { struct stat stat; void *fdm; char const *file; int fd; file = argv[1]; fd = open (file, O_RDONLY); if (fstat (fd, &stat) == -1 || stat.st_size == 0) return -1; fdm = mmap (0, stat.st_size, PROT_READ, MAP_SHARED, fd, 0); if (fdm == MAP_FAILED) return -1; if (init_alsa () == -1) { fprintf (stderr, "init_alsa() error/n"); return -1; } decode (fdm, stat.st_size); if (munmap (fdm, stat.st_size) == -1) return -1; return 0; } static int init_alsa () { snd_pcm_stream_t stream = SND_PCM_STREAM_PLAYBACK; char *pcm_name; int rate = SAMPLE_RATE; /* Sample rate */ int exact_rate; /* Sample rate returned by */ pcm_name = strdup (PCM_DEVICE); snd_pcm_hw_params_alloca (&hwparams); if (snd_pcm_open (&pcm_handle, pcm_name, stream, 0) < 0) { fprintf (stderr, "Error opening PCM device %s/n", pcm_name); return -1; } if (snd_pcm_hw_params_any (pcm_handle, hwparams) < 0) { fprintf (stderr, "Can not configure this PCM device./n"); return -1; } if (snd_pcm_hw_params_set_access (pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) { fprintf (stderr, "Error setting access./n"); return -1; } if (snd_pcm_hw_params_set_format (pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE) < 0) { fprintf (stderr, "Error setting format./n"); return -1; } exact_rate = rate; if (snd_pcm_hw_params_set_rate_near (pcm_handle, hwparams, &exact_rate, 0) < 0) { fprintf (stderr, "Error setting rate./n"); return -1; } if (rate != exact_rate) { fprintf (stderr, "The rate %d Hz is not supported by your hardware./n==> Using %d Hz instead./n", rate, exact_rate); } if (snd_pcm_hw_params_set_channels (pcm_handle, hwparams, CHANNELS) < 0) { fprintf (stderr, "Error setting channels./n"); return -1; } if (snd_pcm_hw_params (pcm_handle, hwparams) < 0) { fprintf (stderr, "Error setting HW params./n"); return -1; } return 0; } static enum mad_flow input (void *data, struct mad_stream *stream) { struct buffer *buffer = data; if (!buffer->length) return MAD_FLOW_STOP; mad_stream_buffer (stream, buffer->start, buffer->length); buffer->length = 0; return MAD_FLOW_CONTINUE; } /*这一段是处理采样后的pcm音频 */ static inline signed int scale (mad_fixed_t sample) { sample += (1L << (MAD_F_FRACBITS - 16)); if (sample >= MAD_F_ONE) sample = MAD_F_ONE - 1; else if (sample < -MAD_F_ONE) sample = -MAD_F_ONE; return sample >> (MAD_F_FRACBITS + 1 - 16); } static enum mad_flow output (void *data, struct mad_header const *header, struct mad_pcm *pcm) { unsigned int nchannels, nsamples, n; mad_fixed_t const *left_ch, *right_ch; unsigned char Output[6912], *OutputPtr; int fmt, wrote, speed, exact_rate, err, dir; nchannels = pcm->channels; n = nsamples = pcm->length; left_ch = pcm->samples[0]; right_ch = pcm->samples[1]; fmt = AFMT_S16_LE; speed = pcm->samplerate * 2; /*播放速度是采样率的两倍 */ OutputPtr = Output; while (nsamples--) { signed int sample; sample = scale (*left_ch++); *(OutputPtr++) = sample >> 0; *(OutputPtr++) = sample >> 8; if (nchannels == 2) { sample = scale (*right_ch++); *(OutputPtr++) = sample >> 0; *(OutputPtr++) = sample >> 8; } } OutputPtr = Output; snd_pcm_writei (pcm_handle, OutputPtr, n); OutputPtr = Output; return MAD_FLOW_CONTINUE; } static enum mad_flow error (void *data, struct mad_stream *stream, struct mad_frame *frame) { return MAD_FLOW_CONTINUE; } static int decode (unsigned char const *start, unsigned long length) { struct buffer buffer; struct mad_decoder decoder; int result; buffer.start = start; buffer.length = length; mad_decoder_init (&decoder, &buffer, input, 0, 0, output, error, 0); mad_decoder_options (&decoder, 0); result = mad_decoder_run (&decoder, MAD_DECODER_MODE_SYNC); mad_decoder_finish (&decoder); return result; }