int avfilter_process_command(AVFilterContext *filter, const char *cmd, const char *arg, char *res, int res_len, int flags) { if(!strcmp(cmd, "ping")){ av_strlcatf(res, res_len, "pong from:%s %s\n", filter->filter->name, filter->name); return 0; }else if(!strcmp(cmd, "enable")) { return set_enable_expr(filter, arg); }else if(filter->filter->process_command) { return filter->filter->process_command(filter, cmd, arg, res, res_len, flags); return AVERROR(ENOSYS);