Each title has a table (VTS_PTT - Video Title Set Part-of-Title Table) that contains 2 pieces of information.
This is the PGCN (ProGram Chain Number) and PGN (ProGram Number) where the chapter starts. Please note - we said the
Program number, not the CELL.
Now we move to the PGC, in it is a list of programs.
Each program begins on a CELL.
Chapter (PTT) -> PGC/Program -> CELL