2.9. Graphical display of chapters in different PGCs

Following are excerpts from the Unofficial DVD specifications Guide 2.2 ebook.

...The DVD specifications do not require chapters or PTTs to belong to the same PGC. The above illustration shows four chapters in two separate PGCs. Even though the chapter number is increased sequentially, the program number starts from 1 again for each PGC. Different PGCs may point to the same cells physically located on a DVD disc. In this scenario, both PGCs point to the same cells 6 and 7. Most authoring programs assign different labels to differentiate the same cells in different PGCs. Since the cells are uniquely identified by their vob id and cell id, PGCs have only pointers to these cells so actually no video, audio or other stream data are duplicated. Commercial DVDs usually have a large number of PGCs in order to...