libavformat/matroskadec.c:834: error: Uninitialized Value
  The value read from length was never initialized.

libavformat/matroskadec.c:834:29: 
832.     case EBML_PASS:  return ebml_parse_id(matroska, syntax->def.n, id, data);
833.     case EBML_STOP:  return 1;
834.     default:         return avio_skip(pb,length)<0 ? AVERROR(EIO) : 0;
                                 ^
835.     }
836.     if (res == AVERROR_INVALIDDATA)
