AVClass* avcl = ptr; if(!avcl || !avcl->class_name) avcl = &av_null_class;
AVClass* avc= ptr ? *(AVClass**)ptr : NULL;
static void av_log_default_callback(void* ptr, int level, const char* fmt, va_list vl){    static int print_prefix=1;    AVClass* avcl = ptr;    if(!avcl || !avcl->class_name)	avcl = &av_null_class;    if(level>av_log_level)	return;#undef fprintf    if(print_prefix) {	    fprintf(stderr, "[%s:%s @ %p]", avcl->class_name, avcl->item_name(avcl), avcl);    }#define fprintf please_use_av_log            print_prefix= strstr(fmt, "\n") != NULL;            vfprintf(stderr, fmt, vl);}