ALSA lib调用实例

最新推荐文章于 2025-05-14 09:48:53 发布
原创 最新推荐文章于 2025-05-14 09:48:53 发布 · 3.3k 阅读 · 3 ·
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1. Display Some PCM Types and Formats 
#include <alsa/asoundlib.h>

int main() {
  int val;

  printf("ALSA library version: %s\n",
          SND_LIB_VERSION_STR);

  printf("\nPCM stream types:\n");
  for (val = 0; val <= SND_PCM_STREAM_LAST; val++)
    printf("  %s\n",
      snd_pcm_stream_name((snd_pcm_stream_t)val));

  printf("\nPCM access types:\n");
  for (val = 0; val <= SND_PCM_ACCESS_LAST; val++)
    printf("  %s\n",
      snd_pcm_access_name((snd_pcm_access_t)val));

  printf("\nPCM formats:\n");
  for (val = 0; val <= SND_PCM_FORMAT_LAST; val++)
    if (snd_pcm_format_name((snd_pcm_format_t)val)
      != NULL)
      printf("  %s (%s)\n",
        snd_pcm_format_name((snd_pcm_format_t)val),
        snd_pcm_format_description(
                           (snd_pcm_format_t)val));

  printf("\nPCM subformats:\n");
  for (val = 0; val <= SND_PCM_SUBFORMAT_LAST;
       val++)
    printf("  %s (%s)\n",
      snd_pcm_subformat_name((
        snd_pcm_subformat_t)val),
      snd_pcm_subformat_description((
        snd_pcm_subformat_t)val));

  printf("\nPCM states:\n");
  for (val = 0; val <= SND_PCM_STATE_LAST; val++)
    printf("  %s\n",
           snd_pcm_state_name((snd_pcm_state_t)val));

  return 0;
}

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, 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(¶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, 2);

  /* 44100 bits/second sampling rate (CD quality) */
  val = 44100;
  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 < 0) {
    fprintf(stderr,
            "unable to set hw parameters: %s\n",
            snd_strerror(rc));
    exit(1);
  }

  /* 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 0;
}

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, 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(¶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, 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;

  while (loops > 0) {
    loops--;
    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);
    }
    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 < 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;
}
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, 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(¶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, 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);
  loops = 5000000 / val;

  while (loops > 0) {
    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 < 0) {
      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(1, 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 0;
}
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[1], "rb");
	if (!fp) {
		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(¶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, 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);

	fseek(fp, 44, SEEK_SET);
	while (1) {
		rc = fread(buffer, 1, size, fp);
		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);
		}
		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 < 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);
	fclose(fp);
	free(buffer);

	return 0;
}

参考： http://www.linuxjournal.com/article/6735
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alsa用户空间编程
luckywang1103的专栏
09-15 5960
alsa由以下几个部分组成： 1) driver内核驱动程序，包括硬件相关的和一些公共代码，了解可参考《writing an ALSA Driver》 2) library用户空间的函数库，需要包含头文件asoundlib.h，链接共享库libasound.so 3) lib-plugins提供了两个插件，一个用jack模拟alsa接口，一个用oss来模拟alsa接口。alsa可以作为jack
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