libavformat/matroskadec.c:721: error: Uninitialized Value
  The value read from length was never initialized.

libavformat/matroskadec.c:721:28: 
719.     case EBML_FLOAT: res = ebml_read_float (pb, length, data);  break;
720.     case EBML_STR:
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)
