ALSA【一】
ALSA是Advanced Linux Sound Architecture 的缩写，目前已经成为了linux的主流音频体系结构。
在内核设备驱动层，ALSA提供了alsa-driver，同时在应用层，ALSA为我们提供了alsa-lib，应用程序只要调用alsa-lib提供的API，即可以完成对底层音频硬件的控制。
实现录音功能代码：
/*
This example reads from the default PCM device
and writes to standard output for 5 seconds of data.
*/
#include
#include
#define BUFFERSIZE 4096
#define PERIOD_SIZE 1024
#define PERIODS 2
#define SAMPLE_RATE 16000
#define CHANNELS 2
#define FSIZE 2*CHANNELS
/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API
int main(int argc, char *argv[]) {
long loops; //define the record time.
int rc; //return code.
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
int err;
char *file;
int fd;
if(argc ==2)
{
file = argv[1];
}
else
{
file = "output.raw";
}
fd = open(file,O_WRONLY|O_CREAT,0777);
if( fd ==-1)
{
printf("open file:%s fail.\n",file);
exit(1);
}
/* Open PCM device for recording (capture). */
err = snd_pcm_open(&handle, "default",SND_PCM_STREAM_CAPTURE, 0);
if (err < 0) {
fprintf(stderr,"unable to open pcm device: %s\n",
snd_strerror(err));
exit(1);
}
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(¶ms);
/* Fill it in with default values. */
err=snd_pcm_hw_params_any(handle, params);
if (err < 0) {
fprintf(stderr, "Can not configure this PCM device: %s\n",
snd_strerror(err));
exit(1);
}
/* Set the desired hardware parameters. */
/* Interleaved mode */
err=snd_pcm_hw_params_set_access(handle, params,SND_PCM_ACCESS_RW_INTERLEAVED);
if (err < 0) {
fprintf(stderr,
"Failed to set PCM device to interleaved: %s\n",
snd_strerror(err));
exit(1);
}
/* Signed 16-bit little-endian format */
err=snd_pcm_hw_params_set_format(handle, params,SND_PCM_FORMAT_S16_LE);
if (err < 0) {
fprintf(stderr,
"Failed to set PCM device to 16-bit signed PCM: %s\n",
snd_strerror(err));
exit(1);
}
/* One channels (mono) */
err=snd_pcm_hw_params_set_channels(handle, params, CHANNELS);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to mono: %s\n",
snd_strerror(err));
exit(1);
}
/* 16000 bits/second sampling rate (CD quality) */
val = SAMPLE_RATE;
err=snd_pcm_hw_params_set_rate_near(handle, params,&val, &dir);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to sample rate =%d: %s\n",
val,snd_strerror(err));
exit(1);
}
/* Set buffer time 500000. */
unsigned int buffer_time,period_time;
snd_pcm_hw_params_get_buffer_time_max(params, &buffer_time, 0);
if ( buffer_time >500000)
buffer_time = 500000;
period_time = buffer_time / 4;
err = snd_pcm_hw_params_set_buffer_time_near(handle, params, &buffer_time, 0);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to buffer time =%d: %s\n",
buffer_time,snd_strerror(err));
exit(1);
}
err = snd_pcm_hw_params_set_period_time_near(handle, params, &period_time, 0);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to period time =%d: %s\n",
period_time,snd_strerror(err));
exit(1);
}
/* Write the parameters to the driver */
err = snd_pcm_hw_params(handle, params);
if (err < 0) {
fprintf(stderr,"unable to set hw parameters: %s\n",
snd_strerror(err));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params,&frames, &dir);
size = frames * FSIZE; /* 2 bytes/sample, 1 channels */
buffer = (char *) malloc(size);
printf("period size = %d frames\n", (int)frames);
printf("read buffer size = %d\n",size);
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params,&val, &dir);
printf("period time is: %d\n",val);
loops = 100;
/*print alsa config parameter*/
snd_pcm_hw_params_get_buffer_time(params, &val, &dir);
printf("buffer time = %d us\n", val);
snd_pcm_hw_params_get_buffer_size(params, (snd_pcm_uframes_t *) &val);
printf("buffer size = %d frames\n", val);
snd_pcm_hw_params_get_periods(params, &val, &dir);
printf("periods per buffer = %d frames\n", val);
while (loops > 0) {
loops--;
rc = snd_pcm_readi(handle, buffer, frames);
if (rc == -EPIPE) {
// EPIPE means overrun
fprintf(stderr, "overrun occurred\n");
err=snd_pcm_prepare(handle);
if( err <0){
fprintf(stderr, "Failed to recover form overrun : %s\n",
snd_strerror(err));
exit(1);
}
}
else if (rc < 0) {
fprintf(stderr,"error from read: %s\n",snd_strerror(rc));
exit(1);
}
else if (rc != (int)frames) {
fprintf(stderr, "short read, read %d frames\n", rc);
}
rc = write(fd, buffer, size);
if (rc <0){
perror("fail to write to audio file\n");
}
}
close(fd);
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
return 0;
}
实现播放声音代码：
#define ALSA_PCM_NEW_HW_PARAMS_API
//#include "alsahead.h"
#include
#include
#define BUFFERSIZE 4096
#define PERIOD_SIZE 1024
#define PERIODS 2
#define SAMPLE_RATE 16000
#define CHANNELS 2
#define FSIZE 2*CHANNELS
/*
*Usage: play audio.raw
*
*/
int main(int argc, char *argv[]) {
long loops;
int rc;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
char *inFile;
int fd;
int err;
if(argc ==2)
{
inFile = argv[1];
}
else
{
inFile = "output.raw";
}
fd = open(inFile,O_RDONLY);
rc = snd_pcm_open(&handle, "default",SND_PCM_STREAM_PLAYBACK, 0);
if (rc < 0) {
fprintf(stderr,"unable to open pcm device: %s\n",snd_strerror(rc));
exit(1);
}
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(¶ms);
/* Fill it in with default values. */
err=snd_pcm_hw_params_any(handle, params);
if (err < 0) {
fprintf(stderr, "Can not configure this PCM device: %s\n",
snd_strerror(err));
exit(1);
}
/* Set the desired hardware parameters. */
/* Interleaved mode */
err=snd_pcm_hw_params_set_access(handle, params,SND_PCM_ACCESS_RW_INTERLEAVED);
if (err < 0) {
fprintf(stderr,
"Failed to set PCM device to interleaved: %s\n",
snd_strerror(err));
exit(1);
}
/* Signed 16-bit little-endian format */
err=snd_pcm_hw_params_set_format(handle, params,SND_PCM_FORMAT_S16_LE);
if (err < 0) {
fprintf(stderr,
"Failed to set PCM device to 16-bit signed PCM: %s\n",
snd_strerror(err));
exit(1);
}
/* One channels (mono) */
err=snd_pcm_hw_params_set_channels(handle, params, CHANNELS);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to mono: %s\n",
snd_strerror(err));
exit(1);
}
/* 16000 bits/second sampling rate (CD quality) */
val = SAMPLE_RATE;
err=snd_pcm_hw_params_set_rate_near(handle, params,&val, &dir);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to sample rate =%d: %s\n",
val,snd_strerror(err));
exit(1);
}
/*
frames = PERIOD_SIZE;
snd_pcm_hw_params_set_period_size_near(handle,params, &frames, &dir);
*/
/*
snd_pcm_hw_params_get_buffer_time_max(params, &buffer_time, 0);
period_time = buffer_time / 4;
err=snd_pcm_hw_params_set_period_time_near(handle, params,&period_time, 0);
if (err < 0) {
fprintf(stderr,"Failed to set PCM device to period time =%u: %s\n",
period_time,snd_strerror(err));
exit(1);
}
*/
unsigned int buffer_time,period_time;
snd_pcm_hw_params_get_buffer_time_max(params, &buffer_time, 0);
if ( buffer_time >500000)
buffer_time = 500000;
period_time = buffer_time / 4;
err = snd_pcm_hw_params_set_buffer_time_near(handle, params, &buffer_time, 0);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to buffer time =%d: %s\n",
buffer_time,snd_strerror(err));
exit(1);
}
err = snd_pcm_hw_params_set_period_time_near(handle, params, &period_time, 0);
if (err < 0) {
fprintf(stderr, "Failed to set PCM device to period time =%d: %s\n",
period_time,snd_strerror(err));
exit(1);
}
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr,"unable to set hw parameters: %s\n",snd_strerror(rc));
exit(1);
}
snd_pcm_hw_params_get_period_size(params, &frames,&dir);
size = frames * FSIZE;
buffer = (char *) malloc(size);
printf("period size = %d frames\n", (int)frames);
printf("read buffer size = %d\n",size);
snd_pcm_hw_params_get_period_time(params,&val, &dir);
printf("period time is: %d\n",val);
loops = 100;
snd_pcm_hw_params_get_buffer_time(params,
&val, &dir);
printf("buffer time = %d us\n", val);
snd_pcm_hw_params_get_buffer_size(params,
(snd_pcm_uframes_t *) &val);
printf("buffer size = %d frames\n", val);
snd_pcm_hw_params_get_periods(params, &val, &dir);
printf("periods per buffer = %d frames\n", val);
while (loops > 0) {
loops--;
rc = read(fd, buffer, size);
if (rc == 0) {
fprintf(stderr, "end of file on input\n");
break;
}
else if (rc != size) {
fprintf(stderr,"short read: read %d bytes\n", rc);
}
rc = snd_pcm_writei(handle, buffer, frames);
if (rc == -EPIPE) {
fprintf(stderr, "underrun occurred\n");
err=snd_pcm_prepare(handle);
if( err <0){
fprintf(stderr, "can not recover from underrun: %s\n",snd_strerror(err));
}
}
else if (rc < 0) {
fprintf(stderr,"error from writei: %s\n",snd_strerror(rc));
}
else if (rc != (int)frames) {
fprintf(stderr,"short write, write %d frames\n", rc);
}
}
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
close(fd);
return 0;
}