NBC sound with libao and C

nbc.c

/*
 *
 * nbc.c
 *
 *     Modified by DJ Heaney - August 2013
 *     Original code (public domain) by Stan Seibert - July 2001
 *
 * Legal Terms:
 *
 *     This source file is released into the public domain.  It is
 *     distributed without any warranty; without even the implied
 *     warranty * of merchantability or fitness for a particular
 *     purpose.
 *
 * Function:
 *
 *     Plays the famous NBC thing.
 *
 * Compilation:
 *
 *     gcc -lao -ldl -lm -o nbc nbc.c
 *
 */

#include <stdio.h>
#include <ao/ao.h>
#include <math.h>
#include <string.h>

#define BUF_SIZE 4096

int main(int argc, char **argv)
{
  ao_device *device;
	ao_sample_format format;
	int default_driver;
	char *buffer;
	int buf_size;
	int sample;
	float freqs[3] = { 261.6, 440.0, 349.2 };
	int i, j;

	/* -- Initialize -- */

	ao_initialize();

	/* -- Setup for default driver -- */

	default_driver = ao_default_driver_id();

        memset(&format, 0, sizeof(format));
	format.bits = 16;
	format.channels = 2;
	format.rate = 44100;
	format.byte_format = AO_FMT_LITTLE;

	/* -- Open driver -- */
	device = ao_open_live(default_driver, &format, NULL /* no options */);
	if (device == NULL) {
		fprintf(stderr, "Error opening device.\n");
		return 1;
	}

	/* -- Play some stuff -- */
	buf_size = format.bits/8 * format.channels * format.rate;
	buffer = calloc(buf_size,
			sizeof(char));

	for(j = 0; j <  3; j++) {
		for (i = 0; i < format.rate; i++) {
			sample = (int)(0.75 * 32768.0 *
				sin(2 * M_PI * freqs[j] * ((float) i/format.rate)));

			/* Put the same stuff in left and right channel */
			buffer[4*i] = buffer[4*i+2] = sample & 0xff;
			buffer[4*i+1] = buffer[4*i+3] = (sample >> 8) & 0xff;
		}

		ao_play(device, buffer, buf_size);

	}

	/* -- Close and shutdown -- */
	ao_close(device);

	ao_shutdown();

  return (0);
}