Thanks for the tips, ended up doing most of what you suggested.
I had sent a dual layer master originally, since i didn't know there was the DDP format. This was all new to me so made a few blunders but the discs came back and so far they seem fine.
The press came back asking for new masters, after receiving the dual layer version, so figured out the DDP format, had to rebuild and reformat. The problem is I couldn't 'play' the DDP files (to preview) so the disc name got screwed up and the DVD_ROM contents ended up in the main directly instead of a DVD_ROM folder. Hopefully that won't cause playback problems in some players.
The DVDSP manual says very little about these DDP/CMF formats. DVD-BOY suggested using version 2.0 but my logic might have lead me to use 2.1 (can't remember what i did use...). Still don't know the specifics of the actual recordable dimension of LAYER0 on normal media and an officially pressed disc.
Finding an accurate split point turned out to be a horror, but eventually found a help suggestion in the tucows forums. they suggest doing a temp build where you put in as many chapter markers as you can, then when you do the format you can see which markers fall into a practice split point. Then you rebuild with the markers removed except for one which falls into your desired area. Thought the short chapters would make for places to assign the split but since the disc was backed tight, ended up having to add a new marker for the split. Turns out there was just a 15 second window to place the split without rebuilding with different bitrates or moving content between VTSs.
Also phucked up on the cover art, had set up for the font to be clear to the silver disc surface, but checked off the wrong box so they put in a white back surface which filled in the transparency. Pissed off about that...
Turns out even though my contact was in Australia (www.dualplover.com) the disc were manufactured in Taiwan. (http://www.tsti.com.tw/)
If anyone wants one, send a pm.
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