Well, not the best solution to that problem. Keep in mind, these DCPs can cause issues on real servers. No trouble if you create them for your own, but I would not let a 16:9 container into the wild. That said, 16:9 containers are probably a bit less risky, since a lot of ads used to be converted into 16:9.
ISDCF is currently preparing a document that constraints SMPTE allowed DCP options into a 'best mastering practice' recommendation. Among it, only flat or scope containers. Full container only for testing purposes, not to play to the public.
Not sure if I understand that scaling issue at all. When playing a bluray, these subs are laid out to fit the 1920/1080 raster. When we create a DCP, we should use the 1920/1080 source with the subs inserted exactly the same way, then pad to 1998 with black. If we don't want to pad, but zoom to a full 1998*1080, the placement of the sub bitmaps doesn't need to change? I guess I need to do my own tests to see the issue. Again, admitted, I personally see general subtitles as a clumsy aid to help understanding, and am not inclined to see any beauty in their appearance, as long as I can read them. So, forgive my ignorance there...
- Carsten
