static void opt_input_file(void *optctx, const char *arg)
{
    if (input_filename) {
        av_log(NULL, AV_LOG_ERROR,
                "Argument '%s' provided as input filename, but '%s' was already specified.\n",
                arg, input_filename);
        exit_program(1);
    }
    if (!strcmp(arg, "-"))
        arg = "pipe:";
    input_filename = arg;
}
static void opt_input_file(void *optctx, const char *arg)
{
    if (input_filename) {
        av_log(NULL, AV_LOG_ERROR,
                "Argument '%s' provided as input filename, but '%s' was already specified.\n",
                arg, input_filename);
        exit_program(1);
    }
    if (!strcmp(arg, "-"))
        arg = "pipe:";
    input_filename = arg;
}