DVD authoring,copy,edit questions + misc :)

Hello Folks,

Some of you might be aware I'm currently developing some DVD-Video copy, edit, 
create programs. The DVD-Video code to create DVD-Video images in mkisofs are 
now a integrated part of cdrtools as of version 1.11a27. 

Anyways I now have my eyes and hacking fingers on more elaborate tasks such as 
chapter extraction, DVD-9 split to two DVD-5, etc.. and I have some questions 
in regards to this.

Chapter extraction:
It's not hard to figure out start cell and end cell of a chapter. However when 
I started to analyze the cell information in the "cell playback information 
table entry" I came to a halt. The cells start and endcells simply doesn't 
match. 

No I don't want to just extract a certain playback sequence I simply want to 
have a chunk of data from sector Y to sector X. 

Cell:   2
Start sector: 00002387
End   sector: 0001ecdd

Cell:   3
Start sector: 0000273c
End   sector: 0001f09e

Here it's relatively easy just extract the data between sector 00002387 and 
sector 0001f09e - I'm assuming the sector is relative to the VTS_XX_1.VOB 
start sector, please correct me if I wrong.

The tricky part is when it looks like this:
Cell:   1 
        Start sector: 0036d4d7  
        End   sector: 0036d4db  
Cell:   2 
        Start sector: 002db177  
        End   sector: 002dec78  
Cell:   3 
        Start sector: 0036d4dc  
        End   sector: 0036d4e0  

What should I do?  Extract 002db177  to 002dec78  and then 0036d4d7  to 
0036d4e0?

DVD-9 to two DVD-5:
Lets say that I just ignore all other titles sets on the DVD and I just deal 
with the main feature film. Merging the VTS_XX_0.IFO with some plain vanilla 
IFO or just edit the one I have. Anyways my question is what to do when I 
encounter problems like the "tricky part" above. This could very well be a 
part of the end of the main feature referencing back to a cell in the very 
beginning. 

As for a general question in splitting a title_set, I would like to know if 
you guys and girls has some bright algos where it should be done. E.g. is 
there a easy way to detect where the second layer beginns.    

I also assume that I have to update all sector references in PCI and DSI 
packets in the title sets I split. However is it also necessary to update VOB 
id - must I start at VOB ID 1 or can I simply start at VOB id 6 for example. 


Misc Notes in regards to mkisofs and DVD-Video:

In order to get DVD-Video support integrated in mkisofs I had to make a very 
cut down version of libdvdread. Joerg the maintainer of cdrtools simply 
didn't want to depend on dvdread since it is not portable in his view. 

Hence I stole and wrote some new code in order to subsitute functions that I 
needed from libdvdread. I hope I haven't stepped on anyones toes doing this. 

Maybe a positive side effect of this is that the bsswap.h macros now have a 
new more portable implementation. It can be worth taking a look at it. 

Ohh, Joerg can sound a bit harsh in his portability comments - but he is 
actually quite nice to work with after the ice has metled. I assume that he 
just want to make every one regardless of OS benefit from improvements in 
mkisofs - hence he holds portability very dearly.

Cheers Olaf