我正在linux平台上使用ALSA进行音频捕获。
我可以使用下面的代码捕获音频，我将"默认"设备传递到参数中，它将把音频数据转储到in.pcm文件中。
然而，当我尝试播放in.pcm文件时，我只听到噪音。我正在尝试使用以下命令播放音频：
ffplay -autoexit -f f32le -ac 1 -ar 44100 in.pcm
代码：
#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>
main (int argc, char *argv[])
{
int i;
int err;
char *buffer;
int buffer_frames = 128;
unsigned int rate = 44100;
snd_pcm_t *capture_handle;
snd_pcm_hw_params_t *hw_params;
snd_pcm_format_t format = SND_PCM_FORMAT_FLOAT;
// snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
if ((err = snd_pcm_open (&capture_handle, argv[1], SND_PCM_STREAM_CAPTURE, 0)) < 0) {
fprintf (stderr, "cannot open audio device %s (%s)n",
argv[1],
snd_strerror (err));
exit (1);
}
fprintf(stdout, "audio interface openedn");
if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
fprintf (stderr, "cannot allocate hardware parameter structure (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params allocatedn");
if ((err = snd_pcm_hw_params_any (capture_handle, hw_params)) < 0) {
fprintf (stderr, "cannot initialize hardware parameter structure (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params initializedn");
if ((err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
fprintf (stderr, "cannot set access type (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params access settedn");
if ((err = snd_pcm_hw_params_set_format (capture_handle, hw_params, format)) < 0) {
fprintf (stderr, "cannot set sample format (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params format settedn");
if ((err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, &rate, 0)) < 0) {
fprintf (stderr, "cannot set sample rate (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params rate settedn");
if ((err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 2)) < 0) {
fprintf (stderr, "cannot set channel count (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params channels settedn");
if ((err = snd_pcm_hw_params (capture_handle, hw_params)) < 0) {
fprintf (stderr, "cannot set parameters (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params settedn");
snd_pcm_hw_params_free (hw_params);
fprintf(stdout, "hw_params freedn");
if ((err = snd_pcm_prepare (capture_handle)) < 0) {
fprintf (stderr, "cannot prepare audio interface for use (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "audio interface preparedn");
buffer = malloc(128 * snd_pcm_format_width(format) / 8 * 2);
fprintf(stdout, "buffer allocatedn");
FILE *fp = fopen("in.pcm", "a+");
//for (i = 0; i < 10; ++i) {
i = 0;
while(++i) {
snd_pcm_wait(capture_handle, 1000);
if ((err = snd_pcm_readi (capture_handle, buffer, buffer_frames)) != buffer_frames) {
fprintf (stderr, "read from audio interface failed (%s)n",
snd_strerror (err));
exit (1);
}
fwrite(buffer, 1, buffer_frames, fp);
fprintf(stdout, "read %d donen", i);
}
fclose(fp);
free(buffer);
fprintf(stdout, "buffer freedn");
snd_pcm_close (capture_handle);
fprintf(stdout, "audio interface closedn");
exit (0);
}
有人能告诉我问题出在哪里吗？
提前谢谢。
我通过更改写函数的缓冲区大小来解决这个问题，并附上我的工作代码：
#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>
main (int argc, char *argv[])
{
int i;
int err;
char *buffer;
int buffer_frames = 128;
unsigned int rate = 44100;
snd_pcm_t *capture_handle;
snd_pcm_hw_params_t *hw_params;
snd_pcm_format_t format = SND_PCM_FORMAT_FLOAT;
// snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
if ((err = snd_pcm_open (&capture_handle, argv[1], SND_PCM_STREAM_CAPTURE, 0)) < 0) {
fprintf (stderr, "cannot open audio device %s (%s)n",
argv[1],
snd_strerror (err));
exit (1);
}
fprintf(stdout, "audio interface openedn");
if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
fprintf (stderr, "cannot allocate hardware parameter structure (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params allocatedn");
if ((err = snd_pcm_hw_params_any (capture_handle, hw_params)) < 0) {
fprintf (stderr, "cannot initialize hardware parameter structure (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params initializedn");
if ((err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
fprintf (stderr, "cannot set access type (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params access settedn");
if ((err = snd_pcm_hw_params_set_format (capture_handle, hw_params, format)) < 0) {
fprintf (stderr, "cannot set sample format (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params format settedn");
if ((err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, &rate, 0)) < 0) {
fprintf (stderr, "cannot set sample rate (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params rate settedn");
if ((err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 2)) < 0) {
fprintf (stderr, "cannot set channel count (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params channels settedn");
if ((err = snd_pcm_hw_params (capture_handle, hw_params)) < 0) {
fprintf (stderr, "cannot set parameters (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "hw_params settedn");
snd_pcm_hw_params_free (hw_params);
fprintf(stdout, "hw_params freedn");
if ((err = snd_pcm_prepare (capture_handle)) < 0) {
fprintf (stderr, "cannot prepare audio interface for use (%s)n",
snd_strerror (err));
exit (1);
}
fprintf(stdout, "audio interface preparedn");
buffer = malloc(128 * snd_pcm_format_width(format) / 8 * 2);
fprintf(stdout, "buffer allocated %dn", snd_pcm_format_width(format) / 8 * 2);
int fd = open("in.pcm", O_CREAT | O_RDWR, 0666);
//for (i = 0; i < 10; ++i) {
i = 0;
while(++i) {
//snd_pcm_wait(capture_handle, 1000);
if ((err = snd_pcm_readi (capture_handle, buffer, buffer_frames)) != buffer_frames) {
fprintf (stderr, "read from audio interface failed (%s)n",
snd_strerror (err));
exit (1);
}
write(fd, buffer, 128 * snd_pcm_format_width(format) / 8 * 2);
fprintf(stdout, "read %d donen", i);
}
close(fd);
free(buffer);
fprintf(stdout, "buffer freedn");
snd_pcm_close (capture_handle);
fprintf(stdout, "audio interface closedn");
exit (0);
}