[Linux_音频]_0_0_使用alsa的API,设置和获得声音

只是一个使用alsa的API,设置和获得声音的入门例子,

之后的事情就参考API自己玩吧.

api网址:http://www.alsa-project.org/alsa-doc/alsa-lib/group___simple_mixer.html

也可以参考alsa-unit的程序代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <stdarg.h>
#include <ctype.h>
#include <math.h>
#include <errno.h>
#include <assert.h>
#include <alsa/asoundlib.h>
#include <sys/poll.h>
#include <stdint.h>
#include "amixer.h"
//使用 amixer scontrols,中的选项
char * sctrlstr = "Digital Input";
int main()
{
	setCapVal();
	return 0;
}


//一个简单使用的例子
int setCapVal()
{
    long volMin, volMax, leftVal, rightVal;
	volMin = 0;  //声音范围
	volMax = 0;
	leftVal = 0;  //左右声道音量
	rightVal = 0;
	int err;
	static snd_mixer_t *handle = NULL;
	snd_mixer_elem_t *elem;
	snd_mixer_selem_id_t *sid;
	snd_mixer_selem_id_alloca(&sid);
	
	
	//打开混音器设备
	if ((err = snd_mixer_open(&handle, 0)) < 0) {
		printf("snd_mixer_open Err\n");
		return err;
	}
	
	snd_mixer_attach(handle, "default");
	snd_mixer_selem_register(handle, NULL, NULL);
	snd_mixer_load(handle);
    //循环找到自己想要的element
	elem = snd_mixer_first_elem(handle);
	while(elem)
	{
		//比较element名字是否是我们想要设置的选项
		if ( strcmp( sctrlstr, snd_mixer_selem_get_name (elem)) == 0)
		{
			printf( "elem name : %s\n", snd_mixer_selem_get_name (elem) );
			break;
		}
		//如果不是就继续寻找下一个
	    elem = snd_mixer_elem_next(elem);
	}
	
	if (!elem) {
		printf("snd_mixer_find_selem Err\n");
		snd_mixer_close(handle);
		handle = NULL;
		return -ENOENT;
	}
	
	//输出elem的名字
	printf( "elem name : %s\n", snd_mixer_selem_get_name (elem) );
	
	snd_mixer_selem_get_capture_volume_range(elem, &volMin, &volMax);
	printf("音量范围: %ld -- %ld\n", volMin, volMax);
	
	snd_mixer_handle_events(handle);
	snd_mixer_selem_get_playback_volume(elem, SND_MIXER_SCHN_FRONT_LEFT, &leftVal);
	snd_mixer_selem_get_playback_volume(elem, SND_MIXER_SCHN_FRONT_RIGHT, &rightVal);
	printf("当前音量: leftVal = %ld, rightVal = %ld\n", leftVal, rightVal);
	
	
	//判断是不是单声道
	if( snd_mixer_selem_is_playback_mono( elem) )
	{
		//单声道
		snd_mixer_selem_set_playback_volume(elem,SND_MIXER_SCHN_FRONT_LEFT, 45);
		printf("单声道: 45\n");
	}
	else
	{
		//左音量
		snd_mixer_selem_set_playback_volume(elem,SND_MIXER_SCHN_FRONT_LEFT, 45);
		//右音量
		snd_mixer_selem_set_playback_volume(elem,SND_MIXER_SCHN_FRONT_RIGHT, 67);
		printf("双声道: 45,  67\n");
	}
	
	
	
	//关闭混音器设备
	snd_mixer_close(handle);
	handle = NULL;
}