libasound

#include <alsa/asoundlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>



snd_pcm_t *handle;
#define ALSA_PCM_NEW_HW_PARAMS_API

#include <alsa/asoundlib.h>

int main()
{
  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;
  char *buffer;

  /* Open PCM device for playback. */
  rc = snd_pcm_open(&handle, "hw:0,0",
                    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, 2);

  /* 44100 bits/second sampling rate (CD quality) */
  val = 44100;
  snd_pcm_hw_params_set_rate_near(handle, params,
                                  &val, &dir);

  /* Set period size to 32 frames. */
  frames = 32;
  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);

  /* We want to loop for 5 seconds */
  snd_pcm_hw_params_get_period_time(params,&val, &dir);
  /* 5 seconds in microseconds divided by
   * period time */
  loops = 5000000 / val;

  int fd = open("charging.wav", O_RDWR);
  printf("---%d %d %d %d\n", fd, frames, size, dir);
  while (loops > 0) //循环录音 5 s  
  {
    loops--;
    //rc = read(0, buffer, size);
    rc = read(fd, buffer, 32*4);
    if (rc == 0) //没有读取到数据
    {
      fprintf(stderr, "end of file on input\n");
      break;
    }
    else if (rc != size)//实际读取 的数据 小于 要读取的数据
    {
      fprintf(stderr,"short read: read %d bytes\n", rc);
    }
    
    rc = snd_pcm_writei(handle, buffer, frames);//写入声卡  （放音）
    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);
  free(buffer);

  return 0;
}

对于声音我们一帧数据就是我们声音位数：例如是8位：那么我们一帧数据就是一个字节如果是双通道那就是2 个字节