I'm trying to understand what you are saying.
Is it in your opinion that the DM's VPFE may be missing super frames because it needs the vertical blanking period to do some processing while the input is ignored? The vertical blanking by itself is useless to me.
Can anything be done to tune the TVP5158's registers to make it behave better with the DM368?
How is it possible that the VPFE is losing super-frames if it receives them in 25 fps with 625 lines configuration from two PAL inputs?
Is it not possible that the TVP5158 is losing lines from the original frames?
BR,
Gadi