static void conv444to422 _ANSI_ARGS_((unsigned char *src, unsigned char *dst));
static void conv422to420 _ANSI_ARGS_((unsigned char *src, unsigned char *dst));
static void conv444to422 _ANSI_ARGS_((unsigned char *src, unsigned char *dst));
static void conv422to420 _ANSI_ARGS_((unsigned char *src, unsigned char *dst));