linux下用alsa播放pcm 44100声音的问题

[liZZZAAA]

我的接口为什么一直提示 under run呢，谁会的帮指导一下。 代码如下：

/*
*
* 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, 0);
//rc = snd_pcm_open(&handle, "plughw:0,0",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 =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 * 8;/* 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 = 5000000 / val;
FILE *fp = fopen("./pcm44100.pcm", "rb");
//while (loops-- > 0) {
while (1) {
//loops--;
// rc = read(0, buffer, size)
rc = fread(buffer, 1, size, fp);
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) {
/* 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);
}
}

snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);

return 0;
}

[liZZZAAA]

为什么没人啊

[fly 100%]

估计是没有写进去

[qq446065469]

写太快了，加个条件： if(snd_pcm_wait(handle, 50)){ rc = snd_pcm_writei(handle, buffer, frames); ... }