使用 ALSA 以 PCM 格式录制音频

Question

我正在 linux 平台上使用 ALSA 进行音频捕获。

我可以使用下面的代码捕获音频，我将 "default" 设备传递给参数，它会将音频数据转储到 in.pcm 文件中。

然而，当我尝试播放 in.pcm 文件时，我只听到噪音。我正在尝试使用以下命令播放音频：

ffplay -autoexit -f f32le -ac 1 -ar 44100 in.pcm

代码：

#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>

main (int argc, char *argv[])
{
  int i;
  int err;
  char *buffer;
  int buffer_frames = 128;
  unsigned int rate = 44100;
  snd_pcm_t *capture_handle;
  snd_pcm_hw_params_t *hw_params;
  snd_pcm_format_t format = SND_PCM_FORMAT_FLOAT;
 //   snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;

  if ((err = snd_pcm_open (&capture_handle, argv[1], SND_PCM_STREAM_CAPTURE, 0)) < 0) {
    fprintf (stderr, "cannot open audio device %s (%s)\n", 
             argv[1],
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "audio interface opened\n");

  if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
    fprintf (stderr, "cannot allocate hardware parameter structure (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params allocated\n");

  if ((err = snd_pcm_hw_params_any (capture_handle, hw_params)) < 0) {
    fprintf (stderr, "cannot initialize hardware parameter structure (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params initialized\n");

  if ((err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
    fprintf (stderr, "cannot set access type (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params access setted\n");

  if ((err = snd_pcm_hw_params_set_format (capture_handle, hw_params, format)) < 0) {
    fprintf (stderr, "cannot set sample format (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params format setted\n");

  if ((err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, &rate, 0)) < 0) {
    fprintf (stderr, "cannot set sample rate (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params rate setted\n");

  if ((err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 2)) < 0) {
    fprintf (stderr, "cannot set channel count (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params channels setted\n");

  if ((err = snd_pcm_hw_params (capture_handle, hw_params)) < 0) {
    fprintf (stderr, "cannot set parameters (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params setted\n");

  snd_pcm_hw_params_free (hw_params);

  fprintf(stdout, "hw_params freed\n");

  if ((err = snd_pcm_prepare (capture_handle)) < 0) {
    fprintf (stderr, "cannot prepare audio interface for use (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "audio interface prepared\n");

  buffer = malloc(128 * snd_pcm_format_width(format) / 8 * 2);

  fprintf(stdout, "buffer allocated\n");
  FILE *fp = fopen("in.pcm", "a+");
  //for (i = 0; i < 10; ++i) {
  i = 0;
  while(++i) {
    snd_pcm_wait(capture_handle, 1000);
    if ((err = snd_pcm_readi (capture_handle, buffer, buffer_frames)) != buffer_frames) {
      fprintf (stderr, "read from audio interface failed (%s)\n",
               snd_strerror (err));
      exit (1);
    }
    fwrite(buffer, 1, buffer_frames, fp);
    fprintf(stdout, "read %d done\n", i);
  }
  fclose(fp);

  free(buffer);

  fprintf(stdout, "buffer freed\n");

  snd_pcm_close (capture_handle);
  fprintf(stdout, "audio interface closed\n");

  exit (0);
}

谁能告诉我问题是什么？

提前致谢。

Answer 1

我通过更改写入函数的缓冲区大小解决了这个问题，附上我的工作代码：

#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>

main (int argc, char *argv[])
{
  int i;
  int err;
  char *buffer;
  int buffer_frames = 128;
  unsigned int rate = 44100;
  snd_pcm_t *capture_handle;
  snd_pcm_hw_params_t *hw_params;
  snd_pcm_format_t format = SND_PCM_FORMAT_FLOAT;
 //   snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;

  if ((err = snd_pcm_open (&capture_handle, argv[1], SND_PCM_STREAM_CAPTURE, 0)) < 0) {
    fprintf (stderr, "cannot open audio device %s (%s)\n", 
             argv[1],
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "audio interface opened\n");

  if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
    fprintf (stderr, "cannot allocate hardware parameter structure (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params allocated\n");

  if ((err = snd_pcm_hw_params_any (capture_handle, hw_params)) < 0) {
    fprintf (stderr, "cannot initialize hardware parameter structure (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params initialized\n");

  if ((err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
    fprintf (stderr, "cannot set access type (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params access setted\n");

  if ((err = snd_pcm_hw_params_set_format (capture_handle, hw_params, format)) < 0) {
    fprintf (stderr, "cannot set sample format (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params format setted\n");

  if ((err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, &rate, 0)) < 0) {
    fprintf (stderr, "cannot set sample rate (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params rate setted\n");

  if ((err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 2)) < 0) {
    fprintf (stderr, "cannot set channel count (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params channels setted\n");

  if ((err = snd_pcm_hw_params (capture_handle, hw_params)) < 0) {
    fprintf (stderr, "cannot set parameters (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "hw_params setted\n");

  snd_pcm_hw_params_free (hw_params);

  fprintf(stdout, "hw_params freed\n");

  if ((err = snd_pcm_prepare (capture_handle)) < 0) {
    fprintf (stderr, "cannot prepare audio interface for use (%s)\n",
             snd_strerror (err));
    exit (1);
  }

  fprintf(stdout, "audio interface prepared\n");

  buffer = malloc(128 * snd_pcm_format_width(format) / 8 * 2);

  fprintf(stdout, "buffer allocated %d\n", snd_pcm_format_width(format) / 8 * 2);
    int fd = open("in.pcm", O_CREAT | O_RDWR, 0666);
  //for (i = 0; i < 10; ++i) {
  i = 0;
  while(++i) {
    //snd_pcm_wait(capture_handle, 1000);
    if ((err = snd_pcm_readi (capture_handle, buffer, buffer_frames)) != buffer_frames) {
      fprintf (stderr, "read from audio interface failed (%s)\n",
               snd_strerror (err));
      exit (1);
    }
    write(fd, buffer, 128 * snd_pcm_format_width(format) / 8 * 2);
    fprintf(stdout, "read %d done\n", i);
  }
  close(fd);

  free(buffer);

  fprintf(stdout, "buffer freed\n");

  snd_pcm_close (capture_handle);
  fprintf(stdout, "audio interface closed\n");

  exit (0);
}

使用 ALSA 以 PCM 格式录制音频

Audio recording using ALSA in PCM format

c

linux

audio

alsa

audio-recording