声音设备接口

声音设备接口

      1. 系统环境

       

　　2. 安装音频库

            ubuntu环境下,旧的/dev/dsp接口没有了. 录/放音乐需要先安装音频库文件. 如下:

       

　　3. 声音设备应用举例

例1 : 播放.wav文件

        pacat-simple.c

/***
  http://www.freedesktop.org/software/pulseaudio/doxygen/pacat-simple_8c-example.html

  This file is part of PulseAudio.
  PulseAudio is free software; you can redistribute it and/or modify
  it under the terms of the GNU Lesser General Public License as published
  by the Free Software Foundation; either version 2.1 of the License,
  or (at your option) any later version.
  PulseAudio is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details.
  You should have received a copy of the GNU Lesser General Public License
  along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
***/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <pulse/simple.h>
#include <pulse/error.h>

#define BUFSIZE 1024

int main(int argc, char* argv[]) 
{
#if 1
    /* The Sample format to use */
    static const pa_sample_spec ss = {
        .format = PA_SAMPLE_S16LE,
        .rate = 44100,
        .channels = 2
    };

    pa_simple *s = NULL;
    int ret = 1;
    int error;
    /* replace STDIN with the specified file if needed */
    if (argc > 1) {
        int fd;
        if ((fd = open(argv[1], O_RDONLY)) < 0) {
            fprintf(stderr, __FILE__": open() failed: %s\n", strerror(errno));
            goto finish;
        }
        if (dup2(fd, STDIN_FILENO) < 0) {
            fprintf(stderr, __FILE__": dup2() failed: %s\n", strerror(errno));
            goto finish;
        }
        close(fd);
    }
    /* Create a new playback stream */
    if (!(s = pa_simple_new(NULL, argv[0], PA_STREAM_PLAYBACK, NULL, "playback", &ss, NULL, NULL, &error))) {
        fprintf(stderr, __FILE__": pa_simple_new() failed: %s\n", pa_strerror(error));
        goto finish;
    }
    for (;;) {
        uint8_t buf[BUFSIZE];
        ssize_t r;
#if 0
        pa_usec_t latency;
        if ((latency = pa_simple_get_latency(s, &error)) == (pa_usec_t) -1) {
            fprintf(stderr, __FILE__": pa_simple_get_latency() failed: %s\n", pa_strerror(error));
            goto finish;
        }
        fprintf(stderr, "%0.0f usec    \r", (float)latency);
#endif
        /* Read some data ... */
        if ((r = read(STDIN_FILENO, buf, sizeof(buf))) <= 0) {
            if (r == 0) /* EOF */
                break;
            fprintf(stderr, __FILE__": read() failed: %s\n", strerror(errno));
            goto finish;
        }
        /* ... and play it */
        if (pa_simple_write(s, buf, (size_t) r, &error) < 0) {
            fprintf(stderr, __FILE__": pa_simple_write() failed: %s\n", pa_strerror(error));
            goto finish;
        }
    }
    /* Make sure that every single sample was played */
    if (pa_simple_drain(s, &error) < 0) {
        fprintf(stderr, __FILE__": pa_simple_drain() failed: %s\n", pa_strerror(error));
        goto finish;
    }
    ret = 0;
finish:
    if (s)
        pa_simple_free(s);
    return ret;
#else
    return  0;

#endif
}

  编译链接执行, 输出如下:

可以听到扬声器中发出的音乐了.

其中用到多个动态库文件, 上面的命令链接动态库的顺序有要求, 否则会报错:

hr@huarain:/opt/study/homework/alsa$ gcc -g -o pacat-simple -lpulse -lpulsecommon-4.0 -lpulse-simple pacat-simple.c
/tmp/cc2t4mNL.o：在函数‘main’中：
/opt/study/homework/alsa/pacat-simple.c:58：对‘pa_simple_new’未定义的引用
/opt/study/homework/alsa/pacat-simple.c:59：对‘pa_strerror’未定义的引用
/opt/study/homework/alsa/pacat-simple.c:87：对‘pa_simple_drain’未定义的引用
/opt/study/homework/alsa/pacat-simple.c:81：对‘pa_simple_write’未定义的引用
/opt/study/homework/alsa/pacat-simple.c:82：对‘pa_strerror’未定义的引用
/opt/study/homework/alsa/pacat-simple.c:88：对‘pa_strerror’未定义的引用
/opt/study/homework/alsa/pacat-simple.c:94：对‘pa_simple_free’未定义的引用
collect2: error: ld returned 1 exit status
hr@huarain:/opt/study/homework/alsa$

 

或

hr@huarain:/opt/study/homework/alsa$ gcc -g -o pacat-simple -lpulse -lpulsecommon-4.0 pacat-simple.c -lpulse-simple
/usr/bin/ld: /tmp/cc4aOF4H.o: undefined reference to symbol 'pa_strerror@@PULSE_0'
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/libpulse.so: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
hr@huarain:/opt/study/homework/alsa$

        例2: 录音

        parec-simple.c

        

/***
  http://www.freedesktop.org/software/pulseaudio/doxygen/parec-simple_8c-example.html  

  This file is part of PulseAudio.
  PulseAudio is free software; you can redistribute it and/or modify
  it under the terms of the GNU Lesser General Public License as published
  by the Free Software Foundation; either version 2.1 of the License,
  or (at your option) any later version.
  PulseAudio is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details.
  You should have received a copy of the GNU Lesser General Public License
  along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
***/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <pulse/simple.h>
#include <pulse/error.h>
#define BUFSIZE 1024
/* A simple routine calling UNIX write() in a loop */
static ssize_t loop_write(int fd, const void*data, size_t size) {
    ssize_t ret = 0;
    while (size > 0) {
        ssize_t r;
        if ((r = write(fd, data, size)) < 0)
            return r;
        if (r == 0)
            break;
        ret += r;
        data = (const uint8_t*) data + r;
        size -= (size_t) r;
    }
    return ret;
}
int main(int argc, char*argv[]) 
{
    /* The sample type to use */
    static const pa_sample_spec ss = {
        .format = PA_SAMPLE_S16LE,
        .rate = 44100,
        .channels = 2
    };
    pa_simple *s = NULL;
    int ret = 1;
    int error;
    /* Create the recording stream */
    if (!(s = pa_simple_new(NULL, argv[0], PA_STREAM_RECORD, NULL, "record", &ss, NULL, NULL, &error))) {
        fprintf(stderr, __FILE__": pa_simple_new() failed: %s\n", pa_strerror(error));
        goto finish;
    }
    for (;;) {
        uint8_t buf[BUFSIZE];
        /* Record some data ... */
        if (pa_simple_read(s, buf, sizeof(buf), &error) < 0) {
            fprintf(stderr, __FILE__": pa_simple_read() failed: %s\n", pa_strerror(error));
            goto finish;
        }
        /* And write it to STDOUT */
        if (loop_write(STDOUT_FILENO, buf, sizeof(buf)) != sizeof(buf)) {
            fprintf(stderr, __FILE__": write() failed: %s\n", strerror(errno));
            goto finish;
        }
    }
    ret = 0;
finish:
    if (s)
        pa_simple_free(s);
    return ret;
}

编译链接运行如下:

暂未验证得到的parec.wav文件内容

4. 参考

http://www.freedesktop.org/software/pulseaudio/doxygen/pacat-simple_8c-example.html

http://www.freedesktop.org/software/pulseaudio/doxygen/parec-simple_8c-example.html
http://www.alsa-project.org/main/index.php/Main_Page