【Linux系统编程应用】Linux音频编程实战（一）_linux音频开发

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/soundcard.h>
 
#define LEN 3 /*存储秒数*/
#define RATE 8000 /*采样频率*/
#define SIZE 8  /*量化位数*/
#define CHANNELS 1 /*声道数目*/
 
unsigned char buf[LEN * RATE * SIZE * CHANNELS / 8];
 
int main(void)
{
    int fd = -1;
    int ret = -1;
    int setting = 0x10000;
    int args;
 
    fd = open("/dev/dsp", O_RDWR);
    if (-1 == fd)
    {
        perror("open"); 
        goto err0;
    }
 
    //设置量化位数
    args = SIZE;
    ret = ioctl(fd, SOUND_PCM_WRITE_BITS, &args);
    if (-1 == ret)
    {
        perror("ioctl"); 
        goto err0;
    }
 
    //设置声道数
    args = CHANNELS;
    ret = ioctl(fd, SOUND_PCM_WRITE_CHANNELS, &args);
    if (-1 == ret)
    {
        perror("ioctl"); 
        goto err0;
    }
 
    //设置采样频率
    args = RATE;
    ret = ioctl(fd, SOUND_PCM_WRITE_RATE, &args);
    if (-1 == ret)
    {
        perror("ioctl"); 
        goto err0;
    }
 
    while(1)
    {
        printf("开始录音.....\n"); 
        //录音
        ret = read(fd, buf, sizeof(buf));
        if (ret != sizeof(buf))
        {
            perror("read"); 
        }
        
        //放音
        printf("you say: \n");
        ret = write(fd, buf, sizeof(buf));
        {
            perror("write"); 
        }
 
        //在继续录音之前等待回放结束 
        ret = ioctl(fd, SOUND_PCM_SYNC, 0);
        if (-1 == ret)
        {
            perror("ioctl"); 
        }
    
    }
 
 
    close(fd);
 
    return 0;
err0:
    return -1;
}

/*
 * mixer.c
 */
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/soundcard.h>
/* 用来存储所有可用混音设备的名称 */
const char *sound_device_names[] = SOUND_DEVICE_NAMES;
int fd;                  /* 混音设备所对应的文件描述符 */
int devmask, stereodevs; /* 混音器信息对应的位图掩码 */
char *name;
/* 显示命令的使用方法及所有可用的混音设备 */
void usage()
{
    int i;
    fprintf(stderr, "usage: %s <device> <left-gain%%> <right-gain%%>\n"
            "       %s <device> <gain%%>\n\n"
            "Where <device> is one of:\n", name, name);
    for (i = 0 ; i < SOUND_MIXER_NRDEVICES ; i++)
        if ((1 << i) & devmask) /* 只显示有效的混音设备 */
            fprintf(stderr, "%s ", sound_device_names[i]);
    fprintf(stderr, "\n");
    exit(1);
}
int main(int argc, char *argv[])
{
    int left, right, level;  /* 增益设置 */
    int status;              /* 系统调用的返回值 */
    int device;              /* 选用的混音设备 */
    char *dev;               /* 混音设备的名称 */
    int i;
    name = argv[0];
    /* 以只读方式打开混音设备 */
    fd = open("/dev/mixer", O_RDONLY);
    if (fd == -1) {
        perror("unable to open /dev/mixer");
        exit(1);
    }
 
    /* 获得所需要的信息 */
    status = ioctl(fd, SOUND_MIXER_READ_DEVMASK, &devmask);
    if (status == -1)
        perror("SOUND_MIXER_READ_DEVMASK ioctl failed");
    status = ioctl(fd, SOUND_MIXER_READ_STEREODEVS, &stereodevs);
    if (status == -1)
        perror("SOUND_MIXER_READ_STEREODEVS ioctl failed");
    /* 检查用户输入 */
    if (argc != 3 && argc != 4)
        usage();
    /* 保存用户输入的混音器名称 */
    dev = argv[1];
    /* 确定即将用到的混音设备 */
    for (i = 0 ; i < SOUND_MIXER_NRDEVICES ; i++)
        if (((1 << i) & devmask) && !strcmp(dev, sound_device_names[i]))
            break;
    if (i == SOUND_MIXER_NRDEVICES) { /* 没有找到匹配项 */
        fprintf(stderr, "%s is not a valid mixer device\n", dev);
        usage();
    }
    /* 查找到有效的混音设备 */
    device = i;
    /* 获取增益值 */
    if (argc == 4) {
        /* 左、右声道均给定 */
        left  = atoi(argv[2]);
        right = atoi(argv[3]);
    } else {
        /* 左、右声道设为相等 */
        left  = atoi(argv[2]);
        right = atoi(argv[2]);
    }
 
    /* 对非立体声设备给出警告信息 */
    if ((left != right) && !((1 << i) & stereodevs)) {
        fprintf(stderr, "warning: %s is not a stereo device\n", dev);
    }
 
    /* 将两个声道的值合到同一变量中 */
    level = (right << 8) + left;
 
    /* 设置增益 */
    status = ioctl(fd, MIXER_WRITE(device), &level);
    if (status == -1) {
        perror("MIXER_WRITE ioctl failed");
        exit(1);
    }
    /* 获得从驱动返回的左右声道的增益 */
    left  = level & 0xff;
    right = (level & 0xff00) >> 8;
    /* 显示实际设置的增益 */
    fprintf(stderr, "%s gain set to %d%% / %d%%\n", dev, left, right);
    /* 关闭混音设备 */
    close(fd);
    return 0;
}