Question

我正在尝试使用alsa（asoundlib库）录制音频并将其写入.pcm文件。

这是我的代码，基于https://gist.github.com/albanpeignier/104902和Audio recording using ALSA in PCM format

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

int main(int argc, char *argv[])
{
  int i;
  int err;
  char *buffer; //?
  int buffer_frames = 128; //?
  unsigned int rate = 44100; // Sample rate of 44,1 kHz

  snd_pcm_t *capture_handle;

  snd_pcm_hw_params_t *hw_params;

  //Signed 16 bit Little Endian 
  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");

  //First, we initialize the hwparams structure with the full configuration space of the soundcard.  
  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");

  // Set sample format of Signed 16 bit Little Endian
  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");

  // Set sample rate of 44,1 kHz
  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", 128 * snd_pcm_format_width(format) / 8 * 2);

  //open pcm file to write data to
  int fd = open("MicIn.pcm", O_CREAT | O_RDWR, 0666);

  i = 0;
  //for (i = 0; i < 10; ++i)
  while (++i) {
    if ((err = snd_pcm_readi(capture_handle, buffer, buffer_frames)) != buffer_frames) {
      fprintf(stderr, "%d: read from audio interface failed (%s)\n", err, 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);
}

我尝试了以下方法：

ffplay -autoexit -f f32le -ac 1 -ar 44100 MicIn.pcm使我的音质令人恐怖，但有些白噪声，但至少我能听到录音。我想知道为什么这行得通，因为f32le不是我在代码中使用的格式
ffplay -autoexit -f s16le -ac 1 -ar 44100 MicIn.pcm即使正确的格式也不会发出声音吗？
试图以大胆的方式导入此文件，但数量很少

有人可以帮助我吗？为什么我的质量不好，为什么只能用格式错误的f32le读取？

使用Alsa捕获音频时音质不佳

0 个答案: