Combine 2 DVD titles into 1 DVD-R

I have two DVD titles:

Disc 1: Have two titles and menu of the movie. Title 1 shows Chapter 1 to Chapter 15, but only Chapter 1-8 have contents, Chapter 9-15 are empty. Title 2 contains Extras.

Disc 2: Have two titles. Title 1 contains the remaining Chapter 9-15, with Chapter 1-8 being empty. Title 2 is empty as Extras are already in Disc 1.

How can I combine Chapter 9-15 in Disc 2 to Disc 1’s Chapter 9-15 empty positions so that I can transcode the combined files to one DVD-R?

Please help


I’m not aware of any simple soultion other than to transcode/encode each disk down to 1/2 a dvdr size, extract the menus manually from the disks and then reauthor them in some authoring software, like DVDLab, Maestro, etc. The main problem seams to be linking one menu to the other.