libavformat/matroskadec.c:723: error: Uninitialized Value
  The value read from length was never initialized.

libavformat/matroskadec.c:723:31: 
721.     case EBML_UTF8:  res = ebml_read_ascii (pb, length, data);  break;
722.     case EBML_BIN:   res = ebml_read_binary(pb, length, data);  break;
723.     case EBML_NEST:  if ((res=ebml_read_master(matroska, length)) < 0)
                                   ^
724.                          return res;
725.                      if (id == MATROSKA_ID_SEGMENT)
