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説明する

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説明する

Cプログラムを使ってオーディオをキャプチャして再生しようとしています。そのためにこのチュートリアルを得ました。。私が実行しているプログラムは次のとおりです。

/**
 * Jan Newmarch
 */

#define PERIOD_SIZE 1024
#define BUF_SIZE (PERIOD_SIZE * 2)

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

void print_pcm_state(snd_pcm_t *handle, char *name) {
  switch (snd_pcm_state(handle)) {
  case SND_PCM_STATE_OPEN:
    printf("state open %s\n", name);
    break;

  case SND_PCM_STATE_SETUP:
    printf("state setup %s\n", name);
    break;

  case SND_PCM_STATE_PREPARED:
    printf("state prepare %s\n", name);
    break;

  case SND_PCM_STATE_RUNNING:
    printf("state running %s\n", name);
    break;

  case SND_PCM_STATE_XRUN:
    printf("state xrun %s\n", name);
    break;

  default:
    printf("state other %s\n", name);
    break;

  }
}


int setparams(snd_pcm_t *handle, char *name) {
  snd_pcm_hw_params_t *hw_params;
  int err;


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

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

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

  if ((err = snd_pcm_hw_params_set_format (handle, hw_params, SND_PCM_FORMAT_S16_LE)) < 0) {
    fprintf (stderr, "cannot set sample format (%s)\n",
         snd_strerror (err));
    exit (1);
  }

  unsigned int rate = 48000;    
  if ((err = snd_pcm_hw_params_set_rate_near (handle, hw_params, &rate, 0)) < 0) {
    fprintf (stderr, "cannot set sample rate (%s)\n",
         snd_strerror (err));
    exit (1);
  }
  printf("Rate for %s is %d\n", name, rate);

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

  snd_pcm_uframes_t buffersize = BUF_SIZE;
  if ((err = snd_pcm_hw_params_set_buffer_size_near(handle, hw_params, &buffersize)) < 0) {
    printf("Unable to set buffer size %li: %s\n", BUF_SIZE, snd_strerror(err));
    exit (1);;
  }

  snd_pcm_uframes_t periodsize = PERIOD_SIZE;
  fprintf(stderr, "period size now %d\n", periodsize);
  if ((err = snd_pcm_hw_params_set_period_size_near(handle, hw_params, &periodsize, 0)) < 0) {
    printf("Unable to set period size %li: %s\n", periodsize, snd_strerror(err));
    exit (1);
  }

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

  snd_pcm_uframes_t p_psize;
  snd_pcm_hw_params_get_period_size(hw_params, &p_psize, NULL);
  fprintf(stderr, "period size %d\n", p_psize);

  snd_pcm_hw_params_get_buffer_size(hw_params, &p_psize);
  fprintf(stderr, "buffer size %d\n", p_psize);

  snd_pcm_hw_params_free (hw_params);

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

  return 0;
}

int set_sw_params(snd_pcm_t *handle, char *name) {
  snd_pcm_sw_params_t *swparams;
  int err;

  snd_pcm_sw_params_alloca(&swparams);

  err = snd_pcm_sw_params_current(handle, swparams);
  if (err < 0) {
    fprintf(stderr, "Broken configuration for this PCM: no configurations available\n");
    exit(1);
  }

  err = snd_pcm_sw_params_set_start_threshold(handle, swparams, PERIOD_SIZE);
  if (err < 0) {
    printf("Unable to set start threshold: %s\n", snd_strerror(err));
    return err;
  }
  err = snd_pcm_sw_params_set_avail_min(handle, swparams, PERIOD_SIZE);
  if (err < 0) {
    printf("Unable to set avail min: %s\n", snd_strerror(err));
    return err;
  }

  if (snd_pcm_sw_params(handle, swparams) < 0) {
    fprintf(stderr, "unable to install sw params:\n");
    exit(1);
  }

  return 0;
}

/************** some code from latency.c *****************/

main (int argc, char *argv[])
{
  int i;
  int err;
  int buf[BUF_SIZE];
  snd_pcm_t *playback_handle;
  snd_pcm_t *capture_handle;
  snd_pcm_hw_params_t *hw_params;
  FILE *fin;
  size_t nread;
  snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
  if (argc != 3) {
    fprintf(stderr, "Usage: %s in-card out-card\n", argv[0]);
    exit(1);
  } 

  /**** Out card *******/
  if ((err = snd_pcm_open (&playback_handle, argv[2], SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
    fprintf (stderr, "cannot open audio device %s (%s)\n", 
         argv[2],
         snd_strerror (err));
    exit (1);
  }

  setparams(playback_handle, "playback");
  set_sw_params(playback_handle, "playback");


  /*********** In card **********/

  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);
  }

  setparams(capture_handle, "capture");
  set_sw_params(capture_handle, "capture");

  if ((err = snd_pcm_link(capture_handle, playback_handle)) < 0) {
    printf("Streams link error: %s\n", snd_strerror(err));
    exit(0);
  }

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

  /**************** stuff something into the playback buffer ****************/
  if (snd_pcm_format_set_silence(format, buf, 2*BUF_SIZE) < 0) {
    fprintf(stderr, "silence error\n");
    exit(1);
  }

  int n = 0;
  while (n++ < 2) {
    if (snd_pcm_writei (playback_handle, buf, BUF_SIZE) < 0) {
      fprintf(stderr, "write error\n");
      exit(1);
    }
  }

  /************* COPY ************/
  while (1) {
    int nread;
    if ((nread = snd_pcm_readi (capture_handle, buf, BUF_SIZE)) != BUF_SIZE) {
      if (nread < 0) {
    fprintf (stderr, "read from audio interface failed (%s)\n",
         snd_strerror (nread));
      } else {
    fprintf (stderr, "read from audio interface failed after %d frames\n", nread);
      } 
      snd_pcm_prepare(capture_handle);
      continue;
    }

    if ((err = snd_pcm_writei (playback_handle, buf, nread)) != nread) {
      if (err < 0) {
    fprintf (stderr, "write to audio interface failed (%s)\n",
         snd_strerror (err));
      } else {
    fprintf (stderr, "write to audio interface failed after %d frames\n", err);
      }
      snd_pcm_prepare(playback_handle);
    }
  }


  snd_pcm_drain(playback_handle);   
  snd_pcm_close (playback_handle);
  exit (0);
}

私はそれをコンパイルし、次のパラメータを使用して実行しました。

./playback-capture hw:0 hw:0

私のコードはこれまでうまく機能していますが、今ではUSBサウンドカードを使ってプログラムを実行することにしました。そのために編集します。

/etc/modprobe.d/alsa-base.conf

変更は次のとおりです。

私は代わりに

options snd_usb_audio index=-2
options snd_hda_intel index=-1

そして

options snd_usb_audio index=-1
options snd_hda_intel index=-2

私は代わりに

# Keep snd-usb-audio from beeing loaded as first soundcard
options snd-usb-audio index=-1

そして

# Keep snd-usb-audio from beeing loaded as first soundcard
options snd-usb-audio index=-1

これでコードを実行すると、次の出力が表示されます。

Rate for playback is 48000
period size now 1024
period size 1024
buffer size 2048
Rate for capture is 48000
cannot set channel count (Invalid argument)

それでは、サウンドカードを使ってコードを実行するにはどうすればいいのか教えてくれる人はいますか？

注:-コマンドを実行します。

aplay -l

そして次のような結果が出ました： -

card 0: Device [USB PnP Sound Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: PCH [HDA Intel PCH], device 0: ALC221 Analog [ALC221 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

答え1

プロジェクトの一環として全二重ALSAが欲しい。高度なLinuxサウンドアーキテクチャたとえば、

  1. マイクジャック（ピンク）を介してサウンドカードからサウンドをキャプチャします。
  2. 別のUSBサウンドカード出力（ラインアウトグリーンジャック）で再生します。

コードを少しだけ変更した場合、以下は双方向ALSAキャプチャ再生の例です。

パスワード

/**
 * Jan Newmarch
 */
 
 
/*
 * File name: rec-play-inline.c
 * 
 * compile: gcc rec-play-inline.c -o rec-play-inline -lasound
 * 
 * run: ./rec-play-inline "plughw:2,0" "plughw:0,0"
 * 
 * 
 * */
  

#define PERIOD_SIZE 1024
#define BUF_SIZE (PERIOD_SIZE * 2)

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

void print_pcm_state(snd_pcm_t *handle, char *name) {
  switch (snd_pcm_state(handle)) {
  case SND_PCM_STATE_OPEN:
    printf("state open %s\n", name);
    break;

  case SND_PCM_STATE_SETUP:
    printf("state setup %s\n", name);
    break;

  case SND_PCM_STATE_PREPARED:
    printf("state prepare %s\n", name);
    break;

  case SND_PCM_STATE_RUNNING:
    printf("state running %s\n", name);
    break;

  case SND_PCM_STATE_XRUN:
    printf("state xrun %s\n", name);
    break;

  default:
    printf("state other %s\n", name);
    break;

  }
}


int setparams(snd_pcm_t *handle, char *name) {
  snd_pcm_hw_params_t *hw_params;
  int err;


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

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

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

  if ((err = snd_pcm_hw_params_set_format (handle, hw_params, SND_PCM_FORMAT_S16_LE)) < 0) {
    fprintf (stderr, "cannot set sample format (%s)\n",
         snd_strerror (err));
    exit (1);
  }

  unsigned int rate = 48000;    
  if ((err = snd_pcm_hw_params_set_rate_near (handle, hw_params, &rate, 0)) < 0) {
    fprintf (stderr, "cannot set sample rate (%s)\n",
         snd_strerror (err));
    exit (1);
  }
  printf("Rate for %s is %d\n", name, rate);

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

  snd_pcm_uframes_t buffersize = BUF_SIZE;
  if ((err = snd_pcm_hw_params_set_buffer_size_near(handle, hw_params, &buffersize)) < 0) {
    printf("Unable to set buffer size %li: %s\n", (long int)BUF_SIZE, snd_strerror(err));
    exit (1);;
  }

  snd_pcm_uframes_t periodsize = PERIOD_SIZE;
  fprintf(stderr, "period size now %d\n", (int) periodsize);
  if ((err = snd_pcm_hw_params_set_period_size_near(handle, hw_params, &periodsize, 0)) < 0) {
    printf("Unable to set period size %li: %s\n", periodsize, snd_strerror(err));
    exit (1);
  }

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

  snd_pcm_uframes_t p_psize;
  snd_pcm_hw_params_get_period_size(hw_params, &p_psize, NULL);
  fprintf(stderr, "period size %d\n", (int)p_psize);

  snd_pcm_hw_params_get_buffer_size(hw_params, &p_psize);
  fprintf(stderr, "buffer size %d\n", (int)p_psize);

  snd_pcm_hw_params_free (hw_params);

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

  return 0;
}

int set_sw_params(snd_pcm_t *handle, char *name) {
  snd_pcm_sw_params_t *swparams;
  int err;

  snd_pcm_sw_params_alloca(&swparams);

  err = snd_pcm_sw_params_current(handle, swparams);
  if (err < 0) {
    fprintf(stderr, "Broken configuration for this PCM: no configurations available\n");
    exit(1);
  }

  err = snd_pcm_sw_params_set_start_threshold(handle, swparams, PERIOD_SIZE);
  if (err < 0) {
    printf("Unable to set start threshold: %s\n", snd_strerror(err));
    return err;
  }
  err = snd_pcm_sw_params_set_avail_min(handle, swparams, PERIOD_SIZE);
  if (err < 0) {
    printf("Unable to set avail min: %s\n", snd_strerror(err));
    return err;
  }

  if (snd_pcm_sw_params(handle, swparams) < 0) {
    fprintf(stderr, "unable to install sw params:\n");
    exit(1);
  }

  return 0;
}

/************** some code from latency.c *****************/

int main (int argc, char *argv[])
{
  int i;
  int err;
  int buf[BUF_SIZE];
  snd_pcm_t *playback_handle;
  snd_pcm_t *capture_handle;
  snd_pcm_hw_params_t *hw_params;
  FILE *fin;
  size_t nread;
  snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
  
  ///Check for command line arguments
  if (argc != 3) {
    fprintf(stderr, "Usage: %s input-soundCard  output-soundCard\n", argv[0]);
    exit(1);
  } 
  
  
  /**** Out card *******/
  if ((err = snd_pcm_open (&playback_handle, argv[1], SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
    fprintf (stderr, "cannot open audio device %s (%s)\n", 
         argv[2],
         snd_strerror (err));
    exit (1);
  }

  setparams(playback_handle, "playback");
  set_sw_params(playback_handle, "playback");


  /*********** In card **********/

  if ((err = snd_pcm_open (&capture_handle, argv[2], SND_PCM_STREAM_CAPTURE, 0)) < 0) {
    fprintf (stderr, "cannot open audio device %s (%s)\n", 
         argv[1],
         snd_strerror (err));
    exit (1);
  }

  setparams(capture_handle, "capture");
  set_sw_params(capture_handle, "capture");
  
  
  ///Comment by EE
/*
  if ((err = snd_pcm_link(capture_handle, playback_handle)) < 0) {
    printf("Streams link error: %s\n", snd_strerror(err));
    exit(0);
  }
*/


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

  /**************** stuff something into the playback buffer ****************/
  if (snd_pcm_format_set_silence(format, buf, 2*BUF_SIZE) < 0) {
    fprintf(stderr, "silence error\n");
    exit(1);
  }
  
  
  ///Comment by EE
/*
  int n = 0;
  while (n++ < 2) {
    if (snd_pcm_writei (playback_handle, buf, BUF_SIZE) < 0) {
      fprintf(stderr, "write error\n");
      exit(1);
    }
  }
*/
///



  /************* Capture and Play Voice ***************/
  
  while (1) {
    int nread;
    if ((nread = snd_pcm_readi (capture_handle, buf, BUF_SIZE)) != BUF_SIZE) {
      if (nread < 0) {
    fprintf (stderr, "read from audio interface failed (%s)\n",
         snd_strerror (nread));
      } else {
    fprintf (stderr, "read from audio interface failed after %d frames\n", nread);
      } 
      snd_pcm_prepare(capture_handle);
      continue;
    }
    
    ///added by EE
    snd_pcm_prepare(playback_handle);
    ///
    
    if ((err = snd_pcm_writei (playback_handle, buf, nread)) != nread) {
      if (err < 0) {
    fprintf (stderr, "write to audio interface failed (%s)\n",
         snd_strerror (err));
      } else {
    fprintf (stderr, "write to audio interface failed after %d frames\n", err);
      }
      snd_pcm_prepare(playback_handle);
    }
  }


  snd_pcm_drain(playback_handle);   
  snd_pcm_close (playback_handle);
  exit (0);
  
  return 0;
}

説明する

私のオンボードサウンドカードは次のとおりです。plughw:0,0USBで接続された外部サウンドカードは次のとおりです。plughw:2,0

次のコマンドを実行してこれらの名前を見つけました。

  • 再生デバイスのリストを取得するには：aplay --list--devices
  • キャプチャデバイスのリストを取得するには：arecord --list-devices

源泉

snd_pcm_prepare(playback_handle);電話する前に追加して問題writei()を解決してください。 ALSA：snd_pcm_writeiを呼び出すとバッファが足りません。

関連情報