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\n");
/* 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(&params);  
/* 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\n",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\n",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\n");
}  
/******************打印参数*********************/
snd_pcm_hw_params_get_channels(params, &val);  
printf("channels = %d\n", val);  
snd_pcm_hw_params_get_rate(params, &val, &dir);  
printf("rate = %d bps\n", val);  
snd_pcm_hw_params_get_period_time(params,  
&val, &dir);  
printf("period time = %d us\n", val);  
snd_pcm_hw_params_get_period_size(params,  
&frames, &dir);  
printf("period size = %d frames\n", (int)frames);  
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);  
snd_pcm_hw_params_get_rate_numden(params,  
&val, &val2);  
printf("exact rate = %d/%d bps\n", val, val2);  
val = snd_pcm_hw_params_get_sbits(params);  
printf("significant bits = %d\n", val);  
//snd_pcm_hw_params_get_tick_time(params,  &val, &dir);  
printf("tick time = %d us\n", val);  
val = snd_pcm_hw_params_is_batch(params);  
printf("is batch = %d\n", val);  
val = snd_pcm_hw_params_is_block_transfer(params);  
printf("is block transfer = %d\n", val);  
val = snd_pcm_hw_params_is_double(params);  
printf("is double = %d\n", val);  
val = snd_pcm_hw_params_is_half_duplex(params);  
printf("is half duplex = %d\n", val);  
val = snd_pcm_hw_params_is_joint_duplex(params);  
printf("is joint duplex = %d\n", val);  
val = snd_pcm_hw_params_can_overrange(params);  
printf("can overrange = %d\n", val);  
val = snd_pcm_hw_params_can_mmap_sample_resolution(params);  
printf("can mmap = %d\n", val);  
val = snd_pcm_hw_params_can_pause(params);  
printf("can pause = %d\n", val);  
val = snd_pcm_hw_params_can_resume(params);  
printf("can resume = %d\n", val);  
val = snd_pcm_hw_params_can_sync_start(params);  
printf("can sync start = %d\n", 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\n");
//if(fseek(fp,0,SEEK_SET) < 0)
// printf("put fp start to first error\n ");


/* 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(&params);  
/* 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\n",(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\n",j++); 
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);  


}  
//else printf("fread to buffer success\n");
rc = snd_pcm_writei(handle, buffer, frames);  


if (rc == -EPIPE) {  
/* EPIPE means underrun */  
fprintf(stderr, "underrun occurred\n");  
snd_pcm_prepare(handle);  
} 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);  
}  
}  
/******************打印参数*********************/
snd_pcm_hw_params_get_channels(params, &val);  
printf("channels = %d\n", val);  
snd_pcm_hw_params_get_rate(params, &val, &dir);  
printf("rate = %d bps\n", val);  
snd_pcm_hw_params_get_period_time(params,  
&val, &dir);  
printf("period time = %d us\n", val);  
snd_pcm_hw_params_get_period_size(params,  
&frames, &dir);  
printf("period size = %d frames\n", (int)frames);  
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);  
snd_pcm_hw_params_get_rate_numden(params,  
&val, &val2);  
printf("exact rate = %d/%d bps\n", val, val2);  
val = snd_pcm_hw_params_get_sbits(params);  
printf("significant bits = %d\n", val);  
//snd_pcm_hw_params_get_tick_time(params,  &val, &dir);  
printf("tick time = %d us\n", val);  
val = snd_pcm_hw_params_is_batch(params);  
printf("is batch = %d\n", val);  
val = snd_pcm_hw_params_is_block_transfer(params);  
printf("is block transfer = %d\n", val);  
val = snd_pcm_hw_params_is_double(params);  
printf("is double = %d\n", val);  
val = snd_pcm_hw_params_is_half_duplex(params);  
printf("is half duplex = %d\n", val);  
val = snd_pcm_hw_params_is_joint_duplex(params);  
printf("is joint duplex = %d\n", val);  
val = snd_pcm_hw_params_can_overrange(params);  
printf("can overrange = %d\n", val);  
val = snd_pcm_hw_params_can_mmap_sample_resolution(params);  
printf("can mmap = %d\n", val);  
val = snd_pcm_hw_params_can_pause(params);  
printf("can pause = %d\n", val);  
val = snd_pcm_hw_params_can_resume(params);  
printf("can resume = %d\n", val);  
val = snd_pcm_hw_params_can_sync_start(params);  
printf("can sync start = %d\n", val);  
/*******************************************************************/
snd_pcm_drain(handle);  
snd_pcm_close(handle);  
free(buf);

fclose(fp);

return 0;

}