这里贴上虚拟机ubuntu下alsa的录音程序（capture.c）和播放程序（playback.c）的源码。
首先要测试一下自己的ubuntu是否打开了声音。这个可以打开/系统/首选项/声音 来调节。另外也可以在终端下输入alsaMixer 来调节，之前我的耳机就是只能放音不能录音，因为没有打开一些设置，在进入alsamixer界面后，按F4也就是capture选项，把声音调大就可以录音了。其中有两种模式测验，一种是使用fread和fwrite以读写文件的方式操作，把声卡里的采集到的frame通过dma发送到应用程序的缓存中，先./capture 录音再./playback 放音。另一种是read和write来操作，把输入输出重定向到标准输入和标准输出，下面的程序就可以用./capture > sound.wav 把输出定向到sound.wav文件中，然后./playback < sound.wav 把声音文件传输到playback的输入端。
另外playback只能播放原始的wav文件。不能播放如MP3类型的编码过的音频文件。
capture.c
/*
This example reads from the default PCM device
and writes to standard output for 5 seconds of data.
*/
/* Use the newer ALSA API */
#include <stdio.h>
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>
int main() {
long loops;
int rc,i = 0;
int size;
FILE *fp ;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val,val2;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
if( (fp =fopen("sound.wav","w")) < 0)
printf("open sound.wav fial ");
/* Open PCM device for recording (capture). */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_CAPTURE, 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. */
snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params,
SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params,
SND_PCM_FORMAT_S16_LE);
/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, 2);
/* 44100 bits/second sampling rate (CD quality) */
val = 44100;
snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);
/* Set period size to 32 frames. */
frames = 32;
snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr, "unable to set hw parameters: %s/n",
snd_strerror(rc));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params, &frames, &dir);
size = frames * 4; /* 2 bytes/sample, 2 channels */
printf("size = %d ",size);
buffer = (char *) malloc(size);
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params, &val, &dir);
loops = 10000000 / val;
while (loops > 0) {
loops--;
rc = snd_pcm_readi(handle, buffer, frames);
printf("%d ",i++);
if (rc == -EPIPE) {
/* EPIPE means overrun */
fprintf(stderr, "overrun occurred/n");
snd_pcm_prepare(handle);
} else if (rc < 0) {
fprintf(stderr,
"error from read: %s/n",
snd_strerror(rc));
} else if (rc != (int)frames) {
fprintf(stderr, "short read, read %d frames/n", rc);
}
//rc = fwrite( buffer,1, size,fp);
rc = write(1,buffer,size);
if (rc != size)
fprintf(stderr, "short write: wrote %d bytes/n", rc);
else printf("fwrite buffer success ");
}
/******************打印参数*********************/
snd_pcm_hw_params_get_channels(params, &val);
printf("channels = %d ", val);
snd_pcm_hw_params_get_rate(params, &val, &dir);
printf("rate = %d bps ", val);
snd_pcm_hw_params_get_period_time(params,
&val, &dir);
printf("period time = %d us ", val);
snd_pcm_hw_params_get_period_size(params,
&frames, &dir);
printf("period size = %d frames ", (int)frames);
snd_pcm_hw_params_get_buffer_time(params,
&val, &dir);
printf("buffer time = %d us ", val);
snd_pcm_hw_params_get_buffer_size(params,
(snd_pcm_uframes_t *) &val);
printf("buffer size = %d frames ", val);
snd_pcm_hw_params_get_periods(params, &val, &dir);
printf("periods per buffer = %d frames ", val);
snd_pcm_hw_params_get_rate_numden(params,
&val, &val2);
printf("exact rate = %d/%d bps ", val, val2);
val = snd_pcm_hw_params_get_sbits(params);
printf("significant bits = %d ", val);
//snd_pcm_hw_params_get_tick_time(params, &val, &dir);
printf("tick time = %d us ", val);
val = snd_pcm_hw_params_is_batch(params);
printf("is batch = %d ", val);
val = snd_pcm_hw_params_is_block_transfer(params);
printf("is block transfer = %d ", val);
val = snd_pcm_hw_params_is_double(params);
printf("is double = %d ", val);
val = snd_pcm_hw_params_is_half_duplex(params);
printf("is half duplex = %d ", val);
val = snd_pcm_hw_params_is_joint_duplex(params);
printf("is joint duplex = %d ", val);
val = snd_pcm_hw_params_can_overrange(params);
printf("can overrange = %d ", val);
val = snd_pcm_hw_params_can_mmap_sample_resolution(params);
printf("can mmap = %d ", val);
val = snd_pcm_hw_params_can_pause(params);
printf("can pause = %d ", val);
val = snd_pcm_hw_params_can_resume(params);
printf("can resume = %d ", val);
val = snd_pcm_hw_params_can_sync_start(params);
printf("can sync start = %d ", val);
/*******************************************************************/
snd_pcm_drain(handle);
snd_pcm_close(handle);
fclose(fp);
free(buffer);
return 0
}
playback.c
/*
This example reads standard from input and writes
to the default PCM device for 5 seconds of data.
*/
/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>
#include <stdio.h>
int main() {
long loops;
int rc,j = 0;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val,val2;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
FILE *fp ;
if( (fp = fopen("sound.wav","r")) < 0)//南拳妈妈 - 你不像她.wav
printf("open sound.wav fial ");
//if(fseek(fp,0,SEEK_SET) < 0)
// printf("put fp start to first error ");
/* Open PCM device for playback. */
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. */
snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params,
SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params,
SND_PCM_FORMAT_S16_LE);
/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, 2);
/* 44100 bits/second sampling rate (CD quality) */
val = 44100;
snd_pcm_hw_params_set_rate_near(handle, params,
&val, &dir);
/* Set period size to 32 frames. */
frames = 16; //设置的值没有反应
snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir); //
printf("frames is %d ",(int)frames);
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr, "unable to set hw parameters: %s/n", snd_strerror(rc));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params, &frames,
&dir);
size = frames * 4; /* 2 bytes/sample, 2 channels */
buffer = (char *) malloc(size);
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params, &val, &dir);
/* 5 seconds in microseconds divided by * period time */
loops = 10000000 / val;
while (loops > 0) {
loops--;
//rc = fread(buffer,1, size,fp);
rc = read(0,buffer,size);
//printf("%d ",j++);
if (rc == 0) {
fprintf(stderr, "end of file on input ");
break;
} else if (rc != size) {
fprintf(stderr, "short read: read %d bytes ", rc);
}
//else printf("fread to buffer success ");
rc = snd_pcm_writei(handle, buffer, frames);
if (rc == -EPIPE) {
/* EPIPE means underrun */
fprintf(stderr, "underrun occurred ");
snd_pcm_prepare(handle);
} else if (rc < 0) {
fprintf(stderr, "error from writei: %s ",
snd_strerror(rc));
} else if (rc != (int)frames) {
fprintf(stderr, "short write, write %d frames ", rc);
}
}
/******************打印参数*********************/
snd_pcm_hw_params_get_channels(params, &val);
printf("channels = %d ", val);
snd_pcm_hw_params_get_rate(params, &val, &dir);
printf("rate = %d bps ", val);
snd_pcm_hw_params_get_period_time(params,
&val, &dir);
printf("period time = %d us ", val);
snd_pcm_hw_params_get_period_size(params,
&frames, &dir);
printf("period size = %d frames ", (int)frames);
snd_pcm_hw_params_get_buffer_time(params,
&val, &dir);
printf("buffer time = %d us ", val);
snd_pcm_hw_params_get_buffer_size(params,
(snd_pcm_uframes_t *) &val);
printf("buffer size = %d frames ", val);
snd_pcm_hw_params_get_periods(params, &val, &dir);
printf("periods per buffer = %d frames ", val);
snd_pcm_hw_params_get_rate_numden(params,
&val, &val2);
printf("exact rate = %d/%d bps ", val, val2);
val = snd_pcm_hw_params_get_sbits(params);
printf("significant bits = %d ", val);
//snd_pcm_hw_params_get_tick_time(params, &val, &dir);
printf("tick time = %d us ", val);
val = snd_pcm_hw_params_is_batch(params);
printf("is batch = %d ", val);
val = snd_pcm_hw_params_is_block_transfer(params);
printf("is block transfer = %d ", val);
val = snd_pcm_hw_params_is_double(params);
printf("is double = %d ", val);
val = snd_pcm_hw_params_is_half_duplex(params);
printf("is half duplex = %d ", val);
val = snd_pcm_hw_params_is_joint_duplex(params);
printf("is joint duplex = %d ", val);
val = snd_pcm_hw_params_can_overrange(params);
printf("can overrange = %d ", val);
val = snd_pcm_hw_params_can_mmap_sample_resolution(params);
printf("can mmap = %d ", val);
val = snd_pcm_hw_params_can_pause(params);
printf("can pause = %d ", val);
val = snd_pcm_hw_params_can_resume(params);
printf("can resume = %d ", val);
val = snd_pcm_hw_params_can_sync_start(params);
printf("can sync start = %d ", val);
/*******************************************************************/
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buf);
fclose(fp);
return 0;
}