AVFormatContext * _ctx = NULL;avformat_open_input(&_ctx, _filePath, 0, 0);

    int fill_iobuffer(void * opaque,uint8_t *buf, int bufsize){          if(!feof(fp_open)){              int true_size=fread(buf,1,bufsize,fp_open);              return true_size;          }else{              return -1;          }      }AVFormatContext * _ctx = NULL;unsigned char* _iobuffer = (unsigned char*)av_malloc(32768);AVIOContext* _avio = avio_alloc_context(_iobuffer , 32768 , 0 , NULL,fill_iobuffer,NULL,NULL);_ctx->pb = _avio;fp_open=fopen(_filename,"rb+");  if ((ret = avformat_open_input(&_ctx, "nothing", 0, 0)) < 0) {	printf( "Could not open input file.");}