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[/code]