var _bpf = bpm / 60 / game_get_speed(gamespeed_fps);
var _spb = 1 / (bpm / 60);
if (snd_is_playing(global.currentsong[1]) && inSync == true)
{
    beat = audio_sound_get_track_position(global.currentsong[1]) / _spb;
    beat = frac(beat);
}
else
{
    inSync = false;
    beat += _bpf;
    if (beat >= 1)
        beat -= 1;
}
image_index = beat * (image_number * loopsPerBeat);