static void gray_to_monoblack(AVPicture *dst, AVPicture *src,
static void gray_to_monoblack(AVPicture *dst, const AVPicture *src,
static void gray_to_monoblack(AVPicture *dst, AVPicture *src,                              int width, int height){    gray_to_mono(dst, src, width, height, 0x00);}