c - 在 C 语言中使用 ALSA 在 Raspberry Pi 上进行录音和播放

Question

我正在尝试录制声音并在 C 程序中播放。
就像使用那些终端线一样:

arecord -D plughw:0 -r 16000 sample.wav

作记录，稍后

aplay sample.wav

播放声音。

我使用了这段代码:

/*


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(&params);


  /* 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;
}

我这样编译这个文件:

gcc -o recorder -lasound recorder.c

并运行它:

./recorder < sample.wav

如果我尝试用“aplay sample.wav”播放它，它会发出可怕的嘈杂声音。
但如果我使用“aplay -t raw -f S16_LE -c2 -r44100 sample.wav”
它运作良好。

我做错了什么，是否有一种简单的方法可以捕获音频并在 Raspberry Pi 上播放？

感谢您的时间。

Answer 1

它只是一个基本的东西，当你尝试 aplay sample.wav" “aplay”将寻找波头，它不在您的文件中。所以它使用其他格式(采样频率， channel 等..)。这就是为什么您的音频变得嘈杂的原因。

但是在 aplay -t raw -f S16_LE -c2 -r44100 sample.wav您正在提供所需的所有信息及其工作正常。