opt_image_format(arg);
static void opt_format(const char *arg){    /* compatibility stuff for pgmyuv */    if (!strcmp(arg, "pgmyuv")) {        pgmyuv_compatibility_hack=1;        opt_image_format(arg);        arg = "image2";    }    file_iformat = av_find_input_format(arg);    file_oformat = guess_format(arg, NULL, NULL);    if (!file_iformat && !file_oformat) {        fprintf(stderr, "Unknown input or output format: %s\n", arg);        exit(1);    }}