bttv_buffer_activate_vbi
bttv_buffer_activate_vbi(btv, NULL);
bttv_buffer_activate_vbi(btv, new);
bttv_buffer_activate_vbi(btv, NULL);
bttv_buffer_activate_vbi(btv, btv->cvbi);
int bttv_buffer_activate_vbi(struct bttv *btv,