AVFormatContext* fc = (AVFormatContext*) class_ptr;
AVFormatContext* fc = (AVFormatContext*) ptr;
static const char* format_to_name(void* class_ptr){    AVFormatContext* fc = (AVFormatContext*) class_ptr;    if(fc->iformat) return fc->iformat->name;    else if(fc->oformat) return fc->oformat->name;    else return "NULL";}