libavformat/matroskadec.c:730: error: Uninitialized Value
  The value read from length was never initialized.

libavformat/matroskadec.c:730:22: 
728.     case EBML_PASS:  return ebml_parse_id(matroska, syntax->def.n, id, data);
729.     case EBML_STOP:  *(int *)data = 1;      return 1;
730.     default:         url_fskip(pb, length); return 0;
                          ^
731.     }
732.     if (res == AVERROR_INVALIDDATA)
