Simple alsa recorder example

/// This work is free. You can redistribute it and/or modify it under the
/// terms of the Do What The Fuck You Want To Public License, Version 2,
/// as published by Sam Hocevar. See http://www.wtfpl.net/ for more details.
// gcc -o alsa_record alsa_record.c -lasound
#include <assert.h>
#include <alsa/asoundlib.h>
#include <math.h>
#define FRAMES 100
short buffer[FRAMES*2]; // stereo
int main(int argc, char *argv[]) {
  const char *pcmname = argc == 2 ? argv[1] : "default";
  snd_pcm_t *pcm;
  assert( snd_pcm_open(&pcm, pcmname, SND_PCM_STREAM_CAPTURE, 0) == 0 );
  assert(
    snd_pcm_set_params(pcm, SND_PCM_FORMAT_S16_LE, SND_PCM_ACCESS_RW_INTERLEAVED, 1/*channels*/, 48000/*rate*/, 1, 250*1000/*latency*/) == 0 ||
    snd_pcm_set_params(pcm, SND_PCM_FORMAT_S16_LE, SND_PCM_ACCESS_RW_INTERLEAVED, 2/*channels*/, 48000/*rate*/, 1, 250*1000/*latency*/) == 0
  );

  // Need to set start_threshold
  // PCM reads into readi() buffer and never starts if sizeof(buffer) < start_threshold:
  snd_pcm_sw_params_t *swparams;
  snd_pcm_sw_params_alloca(&swparams);
  assert( snd_pcm_sw_params_current(pcm, swparams) == 0 );
  snd_pcm_uframes_t start_threshold = -1;
  assert( snd_pcm_sw_params_get_start_threshold(swparams, &start_threshold) == 0 );
  fprintf(stderr, "[start_threshold=%d]\n", (int)start_threshold);
  start_threshold = 1;
  assert( snd_pcm_sw_params_set_start_threshold(pcm, swparams, start_threshold) == 0 );
  assert( snd_pcm_sw_params(pcm, swparams) == 0 );

  int i;
  for (i = 0; i < 144000; ) {
    snd_pcm_sframes_t r = snd_pcm_readi(pcm, buffer, FRAMES);
    fprintf(stderr, "snd_pcm_readi(%d)=%d\n", FRAMES, (int)r);
    if (r < 0)
      fprintf(stderr, "snd_pcm_recover()=%d\n", (int)snd_pcm_recover(pcm, r, 1));
    else if (r > 0)
      i += r;
  }
  assert( snd_pcm_close(pcm) == 0 );
  return 0;
}