ALSA lib调用实例

1. Display Some PCM Types and Formats

2. Opening PCM Device and Setting Parameters

/* 

This example opens the default PCM device, sets
some parameters, and then displays the value
of most of the hardware parameters. It does not
perform any sound playback or recording. 

*/  

/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API  

/* All of the ALSA library API is defined
 * in this header */
#include <alsa/asoundlib.h>  

int main() {
  int rc;
  snd_pcm_t *handle;
  snd_pcm_hw_params_t *params;
  unsigned int val, val2;
  int dir;
  snd_pcm_uframes_t frames;  

  /* Open PCM device for playback. */
  rc = snd_pcm_open(&handle, "default",
                    SND_PCM_STREAM_PLAYBACK, );
  if (rc < ) {
    fprintf(stderr,
            "unable to open pcm device: %s\n",
            snd_strerror(rc));
    exit();
  }  

  /* Allocate a hardware parameters object. */
  snd_pcm_hw_params_alloca(¶ms);  

  /* 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, );  

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

  /* Write the parameters to the driver */
  rc = snd_pcm_hw_params(handle, params);
  if (rc < ) {
    fprintf(stderr,
            "unable to set hw parameters: %s\n",
            snd_strerror(rc));
    exit();
  }  

  /* Display information about the PCM interface */  

  printf("PCM handle name = '%s'\n",
         snd_pcm_name(handle));  

  printf("PCM state = %s\n",
         snd_pcm_state_name(snd_pcm_state(handle)));  

  snd_pcm_hw_params_get_access(params,
                          (snd_pcm_access_t *) &val);
  printf("access type = %s\n",
         snd_pcm_access_name((snd_pcm_access_t)val));  

  snd_pcm_hw_params_get_format(params, &val);
  printf("format = '%s' (%s)\n",
    snd_pcm_format_name((snd_pcm_format_t)val),
    snd_pcm_format_description(
                             (snd_pcm_format_t)val));  

  snd_pcm_hw_params_get_subformat(params,
                        (snd_pcm_subformat_t *)&val);
  printf("subformat = '%s' (%s)\n",
    snd_pcm_subformat_name((snd_pcm_subformat_t)val),
    snd_pcm_subformat_description(
                          (snd_pcm_subformat_t)val));  

  snd_pcm_hw_params_get_channels(params, &val);
  printf("channels = %d\n", val);  

  snd_pcm_hw_params_get_rate(params, &val, &dir);
  printf("rate = %d bps\n", val);  

  snd_pcm_hw_params_get_period_time(params,
                                    &val, &dir);
  printf("period time = %d us\n", val);  

  snd_pcm_hw_params_get_period_size(params,
                                    &frames, &dir);
  printf("period size = %d frames\n", (int)frames);  

  snd_pcm_hw_params_get_buffer_time(params,
                                    &val, &dir);
  printf("buffer time = %d us\n", val);  

  snd_pcm_hw_params_get_buffer_size(params,
                         (snd_pcm_uframes_t *) &val);
  printf("buffer size = %d frames\n", val);  

  snd_pcm_hw_params_get_periods(params, &val, &dir);
  printf("periods per buffer = %d frames\n", val);  

  snd_pcm_hw_params_get_rate_numden(params,
                                    &val, &val2);
  printf("exact rate = %d/%d bps\n", val, val2);  

  val = snd_pcm_hw_params_get_sbits(params);
  printf("significant bits = %d\n", val);  

  snd_pcm_hw_params_get_tick_time(params,
                                  &val, &dir);
  printf("tick time = %d us\n", val);  

  val = snd_pcm_hw_params_is_batch(params);
  printf("is batch = %d\n", val);  

  val = snd_pcm_hw_params_is_block_transfer(params);
  printf("is block transfer = %d\n", val);  

  val = snd_pcm_hw_params_is_double(params);
  printf("is double = %d\n", val);  

  val = snd_pcm_hw_params_is_half_duplex(params);
  printf("is half duplex = %d\n", val);  

  val = snd_pcm_hw_params_is_joint_duplex(params);
  printf("is joint duplex = %d\n", val);  

  val = snd_pcm_hw_params_can_overrange(params);
  printf("can overrange = %d\n", val);  

  val = snd_pcm_hw_params_can_mmap_sample_resolution(params);
  printf("can mmap = %d\n", val);  

  val = snd_pcm_hw_params_can_pause(params);
  printf("can pause = %d\n", val);  

  val = snd_pcm_hw_params_can_resume(params);
  printf("can resume = %d\n", val);  

  val = snd_pcm_hw_params_can_sync_start(params);
  printf("can sync start = %d\n", val);  

  snd_pcm_close(handle);  

  return ;
}  

3. Simple Sound Playback

/* 

This example reads standard from input and writes
to the default PCM device for 5 seconds of data. 

*/  

/* Use the newer ALSA API */
#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, "default",
                    SND_PCM_STREAM_PLAYBACK, );
  if (rc < ) {
    fprintf(stderr,
            "unable to open pcm device: %s\n",
            snd_strerror(rc));
    exit();
  }  

  /* Allocate a hardware parameters object. */
  snd_pcm_hw_params_alloca(¶ms);  

  /* 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, );  

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

  /* Set period size to 32 frames. */
  frames = ;
  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 < ) {
    fprintf(stderr,
            "unable to set hw parameters: %s\n",
            snd_strerror(rc));
    exit();
  }  

  /* Use a buffer large enough to hold one period */
  snd_pcm_hw_params_get_period_size(params, &frames,
                                    &dir);
  size = frames * ; /* 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 =  / val;  

  while (loops > ) {
    loops--;
    rc = read(, buffer, size);
    if (rc == ) {
      fprintf(stderr, "end of file on input\n");
      break;
    } else if (rc != size) {
      fprintf(stderr,
              "short read: read %d bytes\n", rc);
    }
    rc = snd_pcm_writei(handle, buffer, frames);
    if (rc == -EPIPE) {
      /* EPIPE means underrun */
      fprintf(stderr, "underrun occurred\n");
      snd_pcm_prepare(handle);
    } else if (rc < ) {
      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 ;
}
 

编译之后，可以用下面的命令来测试：
./example3 < /dev/urandom

4. Simple Sound Recording

/* 

This example reads from the default PCM device
and writes to standard output for 5 seconds of data. 

*/  

/* Use the newer ALSA API */
#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 recording (capture). */
  rc = snd_pcm_open(&handle, "default",
                    SND_PCM_STREAM_CAPTURE, );
  if (rc < ) {
    fprintf(stderr,
            "unable to open pcm device: %s\n",
            snd_strerror(rc));
    exit();
  }  

  /* Allocate a hardware parameters object. */
  snd_pcm_hw_params_alloca(¶ms);  

  /* 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, );  

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

  /* Set period size to 32 frames. */
  frames = ;
  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 < ) {
    fprintf(stderr,
            "unable to set hw parameters: %s\n",
            snd_strerror(rc));
    exit();
  }  

  /* Use a buffer large enough to hold one period */
  snd_pcm_hw_params_get_period_size(params,
                                      &frames, &dir);
  size = frames * ; /* 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);
  loops =  / val;  

  while (loops > ) {
    loops--;
    rc = snd_pcm_readi(handle, buffer, frames);
    if (rc == -EPIPE) {
      /* EPIPE means overrun */
      fprintf(stderr, "overrun occurred\n");
      snd_pcm_prepare(handle);
    } else if (rc < ) {
      fprintf(stderr,
              "error from read: %s\n",
              snd_strerror(rc));
    } else if (rc != (int)frames) {
      fprintf(stderr, "short read, read %d frames\n", rc);
    }
    rc = write(, buffer, size);
    if (rc != size)
      fprintf(stderr,
              "short write: wrote %d bytes\n", rc);
  }  

  snd_pcm_drain(handle);
  snd_pcm_close(handle);
  free(buffer);  

  return ;
}  

录音使用下面的命令测试：
./listing4 > sound.raw
./listing3 < sound.raw

5. wav格式文件播放测试
这个例子是我根据例子3修改而来的，用来播放wav格式音频文件，注意wav文件格式必须是44100、16bit, 2通道。

#include <alsa/asoundlib.h>  

int main(int argc, char *argv[])
{
    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;
    FILE *fp;  

    fp = fopen(argv[], "rb");
    if (!fp) {
        fprintf(stderr,
            "can't open sound file\n");
        exit();
    }  

    /* Open PCM device for playback. */
    rc = snd_pcm_open(&handle, "default",
            SND_PCM_STREAM_PLAYBACK, );
    if (rc < ) {
        fprintf(stderr,
            "unable to open pcm device: %s\n",
            snd_strerror(rc));
        exit();
    }  

    /* Allocate a hardware parameters object. */
    snd_pcm_hw_params_alloca(¶ms);  

    /* 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, );  

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

    /* Set period size to 32 frames. */
    frames = ;
    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 < ) {
        fprintf(stderr,
            "unable to set hw parameters: %s\n",
            snd_strerror(rc));
        exit();
    }  

    /* Use a buffer large enough to hold one period */
    snd_pcm_hw_params_get_period_size(params,
                    &frames, &dir);
    size = frames * ; /* 2 bytes/sample, 2 channels */
    buffer = (char *)malloc(size);  

    fseek(fp, , SEEK_SET);
    while () {
        rc = fread(buffer, , size, fp);
        if (rc == ) {
            fprintf(stderr, "end of file on input\n");
            break;
        } else if (rc != size) {
            fprintf(stderr,
                "short read: read %d bytes\n", rc);
        }
        rc = snd_pcm_writei(handle, buffer, frames);
        if (rc == -EPIPE) {
            /* EPIPE means underrun */
            fprintf(stderr, "underrun occurred\n");
            snd_pcm_prepare(handle);
        } else if (rc < ) {
            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);
    fclose(fp);
    free(buffer);  

    return ;
}
 

参考：http://www.linuxjournal.com/article/6735