You don't actually need any of these modules or video processor chips. Those options are manufactured for technicians and hobbyists that are clueless in video theory and can't do it otherwise (quite apart from the fact that one of those chips on their own probably costs more than the rest of all the other components combined!).

1. What you DO need is a sync separator chip... anything cheap and cheerful that you can get your hands on... LM1881 springs to mind but it doesn't have to be. That chip will provide the Line and Frame timing signals from your Video Input so the PIC knows (a) the Start of the Display Page (Frame), and (b) where it is on the Page (Line) and (c) if the video is being interlaced.

2. Then all you need is a method of mixing the signal generated by the PIC back with the incoming video, to produce a combined Video Out. A 1 cent Transistor and a small splattering of Resistors is about as simple as I can figure it...

The rest is all done in software, with only one exception... if you have a large alphabet of characters, you may need an external EEPROM to hold the character pattern (font) for the display unless you chose a PIC with a sizeable memory in which to build the font table.

Melanie