/* * 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 , 2008/09/17 , SiChuan University , China * * 编译： gcc MyMinimad.c -o MyMinimad -lmad -g -Wall * 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>struct buffer { unsigned char const *start; unsigned long length;};static int sfd;/*声音设备的描述符 */static int decode(unsigned char const *, unsigned long);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 ((sfd = open("/dev/dsp", O_WRONLY)) < 0) {printf("can not open device!!!/n");return 5; } ioctl(sfd, SNDCTL_DSP_SYNC, 0);/*此句可以不要 */ 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; decode(fdm, stat.st_size); if (munmap(fdm, stat.st_size) == -1)return 4; ioctl(sfd, SNDCTL_DSP_RESET, 0); close(sfd); return 0;}staticenum 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);}staticenum 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; 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 */ ioctl(sfd, SNDCTL_DSP_SPEED, &(speed)); ioctl(sfd, SNDCTL_DSP_SETFMT, &fmt); ioctl(sfd, SNDCTL_DSP_CHANNELS, &(pcm->channels)); 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;} } n *= 4;/*数据长度为pcm音频采样的4倍 */ OutputPtr = Output; while (n) {wrote = write(sfd, OutputPtr, n);OutputPtr += wrote;n -= wrote; } OutputPtr = Output; return MAD_FLOW_CONTINUE;}staticenum mad_flow error(void *data, struct mad_stream *stream, struct mad_frame *frame){ return MAD_FLOW_CONTINUE;}staticint 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;}
