#1 Burning Software

Just to make sure I understand your answer to (3) ...

The reason I would need to update the total size during the callbacks is so I know when I've added too many files ... but if I do that update during callbacks, and then compare it with the value I get back from GetSize() (after calling Build), they should give the same answer?

The thing is, I don't need to know when I've added too many files (to fit on the disc), all I need to know is, given the options the user has selected in my program, will their files fit or not? So for me, I think I can build my whole tree, call GetSize(), add 2M and either 15M or 30M, and then if the answer is too large, tell the user they gotta pick different options, and then go back and re-create the tree.

Thinking more about (3) ...

If I add a whole bunch of really small files to the disc, will the file system overhead still be only 2M? It seems like to be careful, I would need to use a more complicated calculation, one that included # of files and # of folders?

No, the reason is - when you add too many files you can ask user to stop doing this (I'm talking about something like "green-yellow-red" slider at the bottom of "disc compilation" f.e. Nero shows to the user). So user would be asked to remove some files himself from compilation. I'd recommend you doing the same.

Yes, you're correct. Files would be padded to the sector size (2KB) each so true size would be a bit larger then just file size itself. You can easily hovever padd file size yourself after receiving "file add" callback.