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A Minimal ALSA Loopback Program
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <alsa/asoundlib.h> | |
#define BUF_BYTES 128 | |
int main (int argc, char *argv[]) { | |
int err; | |
unsigned char buf[BUF_BYTES]; | |
snd_pcm_t *playback_handle; | |
snd_pcm_t *capture_handle; | |
char* device = "default"; | |
if (argc > 1) device = argv[1]; | |
unsigned int rate = 8000; | |
unsigned int nchannels = 2; | |
snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE; | |
unsigned int buf_frames = BUF_BYTES / nchannels / 2; | |
if ((err = snd_pcm_open (&playback_handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) { | |
fprintf (stderr, "cannot open audio device %s (%s)\n", device, snd_strerror (err)); exit (1); | |
} | |
if ((err = snd_pcm_set_params(playback_handle, format, SND_PCM_ACCESS_RW_INTERLEAVED, nchannels, rate, 1, 500000)) < 0) { /* 0.5sec */ | |
fprintf(stderr, "Playback open error: %s\n", snd_strerror(err)); exit(1); | |
} | |
if ((err = snd_pcm_open (&capture_handle, device, SND_PCM_STREAM_CAPTURE, 0)) < 0) { | |
fprintf (stderr, "cannot open audio device %s (%s)\n", device, snd_strerror (err)); exit (1); | |
} | |
if ((err = snd_pcm_set_params(capture_handle, format, SND_PCM_ACCESS_RW_INTERLEAVED, nchannels, rate, 1, 500000)) < 0) { /* 0.5sec */ | |
fprintf(stderr, "capture open error: %s\n", snd_strerror(err)); exit(1); | |
} | |
while(1) { | |
if ((err = snd_pcm_readi (capture_handle, buf, buf_frames)) != buf_frames) { | |
fprintf (stderr, "read from audio interface failed (%s)\n", snd_strerror (err)); exit (1); | |
} | |
if ((err = snd_pcm_writei (playback_handle, buf, buf_frames)) != buf_frames) { | |
fprintf (stderr, "write to audio interface failed (%s)\n", snd_strerror (err)); exit (1); | |
} | |
} | |
fprintf (stderr, "close handles\n"); | |
snd_pcm_close (playback_handle); | |
snd_pcm_close (capture_handle); | |
return 0; | |
} |
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