Streaming Sound

Introduction

This guide focuses on streaming sound on the Sega Dreamcast. Unlike sound effects, streamed sound is not uploaded all-at-once to the Dreamcast AICA RAM. Instead, a small buffer of up to 65536 bytes (per channel) is allocated and refilled while sound plays. Streamed sound can be mono or stereo and supports 16-bit uncompressed PCM, 8-bit PCM, or 4-bit Yamaha ADPCM. You can have up to 4 sound streams playing simultaneously, which doesn't impact sound effects.

Common libraries used to stream sound are libmp3, libogg, and libtremor from kos-ports. These libraries handle most of the work described in the API section, allowing you to skip the API details if you prefer and dive into the code examples.

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API

The KOS reference manual has more details on each function, with most functions implemented in snd_stream.c.

Initialize Sound System

int snd_stream_init();

Stream Callback

typedef void*(* snd_stream_callback_t)(snd_stream_hnd_t hnd, int smp_req, int *smp_recv);

Allocate Sound Stream

snd_stream_hnd_t snd_stream_alloc(snd_stream_callback_t callback, int bufsize);

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Code Example

Below is a sample code demonstrating sound streaming using libtremor for .ogg files. For more details and resources, see the Github repository.

Note: This code may not work in Sega Dreamcast emulators.

#include <kos.h>
#include <oggvorbis/sndoggvorbis.h>

#define LEFT 0
#define CENTER 128
#define RIGHT 255

#define LOOP 1
#define SHAKER_VOL 200
#define INITIAL_CRY 128
#define LOUDEST_CRY 240

static void draw_instructions(uint8_t volume);

static cont_state_t* get_cont_state();
static int button_pressed(unsigned int current_buttons, unsigned int changed_buttons, unsigned int button);

int main(int argc, char **argv) {
    uint8_t baby_volume = INITIAL_CRY;
    uint8_t shake_volume = SHAKER_VOL;

    uint64_t start_time = timer_ms_gettime64();
    uint64_t end_time = start_time;

    cont_state_t* cond;

    vid_set_mode(DM_640x480, PM_RGB555);
    snd_stream_init();
    sndoggvorbis_init();

    sfxhnd_t shake1 = snd_sfx_load("/rd/shake-1.wav");
    sfxhnd_t shake2 = snd_sfx_load("/rd/shake-2.wav");

    sndoggvorbis_volume(baby_volume);
    sndoggvorbis_start("/rd/baby-whining-01.ogg", LOOP);

    unsigned int current_buttons = 0;
    unsigned int changed_buttons = 0;
    unsigned int previous_buttons = 0;

    for(;;) {
        cond = get_cont_state();
        current_buttons = cond->buttons;
        changed_buttons = current_buttons ^ previous_buttons;
        previous_buttons = current_buttons;

        if(button_pressed(current_buttons, changed_buttons, CONT_X)) {
            snd_sfx_play(shake1, shake_volume, LEFT);
            if(baby_volume > 40)
                baby_volume -= 10;
        }
        if(button_pressed(current_buttons, changed_buttons, CONT_Y)) {
            snd_sfx_play(shake2, shake_volume, RIGHT);
            if(baby_volume > 40)
                baby_volume -= 10;
        }
        if(button_pressed(current_buttons, changed_buttons, CONT_A)) {
            if(!sndoggvorbis_isplaying()) {
                baby_volume = INITIAL_CRY;
                sndoggvorbis_volume(baby_volume);
                sndoggvorbis_start("/rd/baby-whining-01.ogg", LOOP);
            }
        }
        if(button_pressed(current_buttons, changed_buttons, CONT_B)) {
            baby_volume = 0;
            sndoggvorbis_stop();
        }
        if(button_pressed(current_buttons, changed_buttons, CONT_START))
            break;

        end_time = timer_ms_gettime64();
        if((end_time - start_time) >= 1000) {
             baby_volume += 15;
             start_time = end_time;
        }

        if(baby_volume > LOUDEST_CRY) {
            baby_volume = LOUDEST_CRY;
        }

        if(baby_volume <= 40) {
            baby_volume = 0;
            sndoggvorbis_stop();
        } else {
            sndoggvorbis_volume(baby_volume);
        }

        draw_instructions(baby_volume);
    }

    snd_sfx_unload_all();
    sndoggvorbis_stop();
    sndoggvorbis_shutdown();
    snd_stream_shutdown();

    return 0;
}

static void draw_instructions(uint8_t baby_volume) {
    int x = 20, y = 20+24;
    int color = 1;
    char baby_status[50];
    memset(baby_status, 0, 50);

    if(baby_volume == 0) {
        snprintf(baby_status, 50, "%-50s", "Baby is asleep!!! Finally...");
    }
    else if(baby_volume > 40 && baby_volume <= 90) {
        snprintf(baby_status, 50, "%-50s", "Baby is almost asleep. Keep rattling!!");
    }
    else if(baby_volume > 90 && baby_volume <= 180) {
        snprintf(baby_status, 50, "%-50s", "You can do better than that!");
    }
    else if(baby_volume > 180 && baby_volume <= LOUDEST_CRY) {
        snprintf(baby_status, 50, "%-50s", "Are you even rattling!?!?!");
    }

    bfont_draw_str_vram_fmt(x, y, true, 
        "Press X and/or Y to play rattle sounds to calm\n"
        "down the baby so it can go to sleep\n"     
        "Press A to wake the baby up\n"
        "Press B to force baby asleep\n"
        "Press Start to exit program\n\n"
        "%s");
    y += 72;
    bfont_draw_str(vram_s + y*640+x, 640, color, baby_status);
}

static cont_state_t* get_cont_state() {
    maple_device_t* cont;
    cont_state_t* state;

    cont = maple_enum_type(0, MAPLE_FUNC_CONTROLLER);
    if(cont) {
        state = (cont_state_t*)maple_dev_status(cont);
        return state;
    }

    return NULL;
}

static int button_pressed(unsigned int current_buttons, unsigned int changed_buttons, unsigned int button) {
    if(changed_buttons & button) {
        if(current_buttons & button)
            return 1;
    }

    return 0;
}

This example demonstrates the use of libtremor to play .ogg files, as well as handling sound effects.