Question

我正在Linux平台上使用ALSA进行音频捕获。

我能够使用下面的代码捕获音频，其中我将“默认”设备传递给参数，它将音频数据转储到val文件中。

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

in.pcm

代码：

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

有人可以告诉我问题是什么吗？

谢谢。

Answer 1

我通过更改写函数的缓冲区大小并附加了我的工作代码来解决此问题：

#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PCM格式的ALSA进行音频录制

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