sdl_audio_test.c

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <SDL/SDL.h>
#ifdef EMSCRIPTEN
#include <emscripten.h>
#else
#include <unistd.h>
#endif

#define NUM_FRAMES 1024
#define NUM_CHANNELS 2
#define NUM_SAMPLES (NUM_FRAMES * NUM_CHANNELS)
#define FREQ_MUL 4

Sint16 buffer[NUM_SAMPLES];

void fill_buffer(void) {
    int i, j;
    Sint16 *p = &buffer[0];
    for (i = 0; i < NUM_SAMPLES / NUM_CHANNELS; i++) {
        Sint16 val = (Sint16)(sin(((double)i * FREQ_MUL / NUM_FRAMES)
                                  * M_PI * 2) * 30000);
        for (j = 0; j < NUM_CHANNELS; j++) {
            *(p++) = val;
        }
    }
}

void audio_callback(void *udata, Uint8 *stream, int len) {
    if (len != sizeof(buffer)) {
        printf("Expected len == %i but got %i\n", (int)sizeof(buffer), len);
        abort();
    }
    memcpy(stream, buffer, len);
}

#ifdef EMSCRIPTEN
void main_loop(void) {
}
#endif

int main(void) {
    SDL_AudioSpec wanted;

    fill_buffer();

    SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO);

    /* Set the audio format */
    wanted.freq = 44100;
    wanted.format = AUDIO_S16SYS;
    wanted.channels = NUM_CHANNELS;
    /* Why this difference? */
#ifdef EMSCRIPTEN
    wanted.samples = NUM_FRAMES;
#else    
    wanted.samples = NUM_SAMPLES;
#endif
    wanted.callback = audio_callback;
    wanted.userdata = NULL;

    /* Open the audio device, forcing the desired format */
    if (SDL_OpenAudio(&wanted, NULL) < 0) {
        printf("Couldn't open audio: %s\n", SDL_GetError());
        return(-1);
    }

    SDL_PauseAudio(0);
#ifdef EMSCRIPTEN
    emscripten_set_main_loop(main_loop, 1, 0);
#else
    sleep(100);
#endif

    return 0;
}