基于alsa驱动架构的pcm播放

/*modify by hfl 2014-2-16*/ /* Use the newer ALSA API */ #define ALSA_PCM_NEW_HW_PARAMS_API #include <alsa/asoundlib.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> int main(int argc, char *argv[]) {   long loops;   int rc;   int size;   snd_pcm_t *handle;   snd_pcm_hw_params_t *params;   unsigned int val;   int dir;   snd_pcm_uframes_t frames;   printf("222133\n");  char buffer[20*2];/*size=frame*channles*byte persaple*/  int fd,i; if (argc != 2) { fprintf (stderr, "usage: %s <filename>!\n", argv[0]); exit ( -1 ) ; } if ( ( fd = open (argv[1],O_RDONLY))<0) { fprintf ( stderr, " Can't open sound file!\n"); exit (-1 ); }   /* Open PCM device for playback. */   rc = snd_pcm_open(&handle, "default",                     SND_PCM_STREAM_PLAYBACK, 0);   if (rc < 0) {     fprintf(stderr,             "unable to open pcm device: %s\n",             snd_strerror(rc));     exit(1);   }   /* Allocate a hardware parameters object. */   snd_pcm_hw_params_alloca(&params);   /* Fill it in with default values. */   snd_pcm_hw_params_any(handle, params);   /* Set the desired hardware parameters. */   /* Interleaved mode */   snd_pcm_hw_params_set_access(handle, params,                       SND_PCM_ACCESS_RW_INTERLEAVED);   /* Signed 16-bit little-endian format */   snd_pcm_hw_params_set_format(handle, params,                               SND_PCM_FORMAT_S16_LE);   /* Two channels (stereo) */   snd_pcm_hw_params_set_channels(handle, params, 1);   /* 44100 bits/second sampling rate (CD quality) */   val = 16000;   snd_pcm_hw_params_set_rate_near(handle, params,                                   &val, &dir);   /* Set period size to 32 frames. */   frames =20;/*一次送人的帧太少，会下溢冲（至少15帧)*/  // snd_pcm_hw_params_set_period_size_near(handle,  params, &frames, &dir);   /* Write the parameters to the driver */   rc = snd_pcm_hw_params(handle, params);   if (rc < 0) {     fprintf(stderr,             "unable to set hw parameters: %s\n",             snd_strerror(rc));     exit(1);   }   /* Use a buffer large enough to hold one period */  // snd_pcm_hw_params_get_period_size(params, &frames,&dir);   //size = frames * 4; /* 2 bytes/sample, 2 channels */  // buffer = (char *) malloc(size); long s=0;  i =0;   while(i = read(fd,buffer, sizeof(buffer))>0) { //s+=i; //printf("s=%ld\n",s);     #if 0     rc = read(0, buffer, size);     if (rc == 0) {       fprintf(stderr, "end of file on input\n");       break;     } else if (rc != size) {       fprintf(stderr,               "short read: read %d bytes\n", rc);     } #endif      rc = snd_pcm_writei(handle, buffer, frames);     if (rc==frames*2) {  printf("read data oK\n"); }     if (rc == -EPIPE) {       /* EPIPE means underrun */       fprintf(stderr, "underrun occurred\n");       snd_pcm_prepare(handle);     } else if (rc < 0) {       fprintf(stderr,               "error from writei: %s\n",               snd_strerror(rc));     }  else if (rc != (int)frames) {       fprintf(stderr,               "short write, write %d frames\n", rc);     }   }   snd_pcm_drain(handle);   snd_pcm_close(handle);   printf("play end \n"); //  free(buffer);   close(fd);   return 0;

}

因为alsa 架构开放给用户的接口不是直接操作驱动，而是操作一个库的接口，相当于在驱动的上层做了一层封装的SDK。因此编译是要链接到一个动态库，并包含相应的头文件。注意alsa架构送数据是以frame为单位送的。size=frames*channel*每个采样的字节数。frame不能太小，否则会产生下溢，造成卡顿。在读文件的环境当中，frame至少15以上。

编译命令：

gcc -o pcmplayalsa pcmplayalsa.c -I/usr/include/alsa -lasound