主音量控制

【轉貼】Fred's blog

#include <stdio.h>
#include <alsa/asoundlib.h>  <--- libasound2-dev
int main(void)
{
  int unmute, chn;
  int al, ar;
  snd_mixer_t *mixer;
  snd_mixer_elem_t *master_element;

  snd_mixer_open(&mixer, 0);
  snd_mixer_attach(mixer, "default");
  snd_mixer_selem_register(mixer, NULL, NULL);
  snd_mixer_load(mixer);

  /* 取得第一個 element，也就是 Master */
  master_element = snd_mixer_first_elem(mixer);
  /* 設定音量的範圍 0 ~ 100 */
  snd_mixer_selem_set_playback_volume_range(master_element, 0, 100);

  /* 取得 Master 是否靜音 */
  snd_mixer_selem_get_playback_switch(master_element, 0, &unmute);
  if (unmute)
      printf("Master is Unmute.\n");
  else
      printf("Master is Mute.\n");

  /* 取得左右聲道的音量 */
  snd_mixer_selem_get_playback_volume(master_element, SND_MIXER_SCHN_FRONT_LEFT, &al);
  snd_mixer_selem_get_playback_volume(master_element, SND_MIXER_SCHN_FRONT_RIGHT, &ar);
  /* 兩聲道相加除以二求平均音量 */
  printf("Master volume is %d\n", (al + ar) >> 1);

  /* 設定 Master 音量 */
  snd_mixer_selem_set_playback_volume(master_element, SND_MIXER_SCHN_FRONT_LEFT, 99);
  snd_mixer_selem_set_playback_volume(master_element, SND_MIXER_SCHN_FRONT_RIGHT, 99);

  /* 將 Master 切換為靜音 */
  for (chn=0;chn<=SND_MIXER_SCHN_LAST;chn++) {
      snd_mixer_selem_set_playback_switch(master_element, chn, 0);
  }

  /* 將 Master 切換為非靜音 */
  for (chn=0;chn<=SND_MIXER_SCHN_LAST;chn++) {
      snd_mixer_selem_set_playback_switch(master_element, chn, 1);
  }
  return 0;
}

compiler :

gcc  t1.c  -o  t1  -lasound

ref :
1. Fred's blog
2. Andes Core