1. Display Some PCM Types and Formats
2. Opening PCM Device and Setting Parameters
/* This example opens the default PCM device, sets
some parameters, and then displays the value
of most of the hardware parameters. It does not
perform any sound playback or recording. */ /* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API /* All of the ALSA library API is defined
* in this header */
#include <alsa/asoundlib.h> int main() {
int rc;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val, val2;
int dir;
snd_pcm_uframes_t frames; /* Open PCM device for playback. */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_PLAYBACK, );
if (rc < ) {
fprintf(stderr,
"unable to open pcm device: %s\n",
snd_strerror(rc));
exit();
} /* 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, ); /* 44100 bits/second sampling rate (CD quality) */
val = ;
snd_pcm_hw_params_set_rate_near(handle,
params, &val, &dir); /* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < ) {
fprintf(stderr,
"unable to set hw parameters: %s\n",
snd_strerror(rc));
exit();
} /* Display information about the PCM interface */ printf("PCM handle name = '%s'\n",
snd_pcm_name(handle)); printf("PCM state = %s\n",
snd_pcm_state_name(snd_pcm_state(handle))); snd_pcm_hw_params_get_access(params,
(snd_pcm_access_t *) &val);
printf("access type = %s\n",
snd_pcm_access_name((snd_pcm_access_t)val)); snd_pcm_hw_params_get_format(params, &val);
printf("format = '%s' (%s)\n",
snd_pcm_format_name((snd_pcm_format_t)val),
snd_pcm_format_description(
(snd_pcm_format_t)val)); snd_pcm_hw_params_get_subformat(params,
(snd_pcm_subformat_t *)&val);
printf("subformat = '%s' (%s)\n",
snd_pcm_subformat_name((snd_pcm_subformat_t)val),
snd_pcm_subformat_description(
(snd_pcm_subformat_t)val)); 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_close(handle); return ;
}
3. Simple Sound Playback
/* 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> int main() {
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; /* Open PCM device for playback. */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_PLAYBACK, );
if (rc < ) {
fprintf(stderr,
"unable to open pcm device: %s\n",
snd_strerror(rc));
exit();
} /* 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, ); /* 44100 bits/second sampling rate (CD quality) */
val = ;
snd_pcm_hw_params_set_rate_near(handle, params,
&val, &dir); /* Set period size to 32 frames. */
frames = ;
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 < ) {
fprintf(stderr,
"unable to set hw parameters: %s\n",
snd_strerror(rc));
exit();
} /* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params, &frames,
&dir);
size = frames * ; /* 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 = / val; while (loops > ) {
loops--;
rc = read(, buffer, size);
if (rc == ) {
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) {
/* EPIPE means underrun */
fprintf(stderr, "underrun occurred\n");
snd_pcm_prepare(handle);
} else if (rc < ) {
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); return ;
}
编译之后，可以用下面的命令来测试：
./example3 < /dev/urandom
4. Simple Sound Recording
/* This example reads from the default PCM device
and writes to standard output for 5 seconds of data. */ /* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API #include <alsa/asoundlib.h> int main() {
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; /* Open PCM device for recording (capture). */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_CAPTURE, );
if (rc < ) {
fprintf(stderr,
"unable to open pcm device: %s\n",
snd_strerror(rc));
exit();
} /* 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, ); /* 44100 bits/second sampling rate (CD quality) */
val = ;
snd_pcm_hw_params_set_rate_near(handle, params,
&val, &dir); /* Set period size to 32 frames. */
frames = ;
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 < ) {
fprintf(stderr,
"unable to set hw parameters: %s\n",
snd_strerror(rc));
exit();
} /* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params,
&frames, &dir);
size = frames * ; /* 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);
loops = / val; while (loops > ) {
loops--;
rc = snd_pcm_readi(handle, buffer, frames);
if (rc == -EPIPE) {
/* EPIPE means overrun */
fprintf(stderr, "overrun occurred\n");
snd_pcm_prepare(handle);
} else if (rc < ) {
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 = write(, buffer, size);
if (rc != size)
fprintf(stderr,
"short write: wrote %d bytes\n", rc);
} snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer); return ;
}
录音使用下面的命令测试：
./listing4 > sound.raw
./listing3 < sound.raw
5. wav格式文件播放测试
这个例子是我根据例子3修改而来的，用来播放wav格式音频文件，注意wav文件格式必须是44100、16bit, 2通道。
#include <alsa/asoundlib.h> int main(int argc, char *argv[])
{
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;
FILE *fp; fp = fopen(argv[], "rb");
if (!fp) {
fprintf(stderr,
"can't open sound file\n");
exit();
} /* Open PCM device for playback. */
rc = snd_pcm_open(&handle, "default",
SND_PCM_STREAM_PLAYBACK, );
if (rc < ) {
fprintf(stderr,
"unable to open pcm device: %s\n",
snd_strerror(rc));
exit();
} /* 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, ); /* 44100 bits/second sampling rate (CD quality) */
val = ;
snd_pcm_hw_params_set_rate_near(handle, params,
&val, &dir); /* Set period size to 32 frames. */
frames = ;
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 < ) {
fprintf(stderr,
"unable to set hw parameters: %s\n",
snd_strerror(rc));
exit();
} /* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params,
&frames, &dir);
size = frames * ; /* 2 bytes/sample, 2 channels */
buffer = (char *)malloc(size); fseek(fp, , SEEK_SET);
while () {
rc = fread(buffer, , size, fp);
if (rc == ) {
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) {
/* EPIPE means underrun */
fprintf(stderr, "underrun occurred\n");
snd_pcm_prepare(handle);
} else if (rc < ) {
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);
fclose(fp);
free(buffer); return ;
}
