if (soundyyopenal != -1) || (is_playing_fmod != false)
{
    show_message_async("Error: a sound is already playing, please click 3.");
    exit;
}
soundfmod = FMODGMS_Snd_LoadStream(working_directory+"bgm.at9");
//soundfmod = FMODGMS_Snd_LoadSound(working_directory+"bgm.at9");
//as mentioned by FMOD Docs, AT9 is useful for music, so LoadStream.
FMODGMS_Snd_PlaySound(soundfmod,channel);
is_playing_fmod = true;
show_message_async("Played bgm.at9 using FMOD!"); // ^-^