I have. and none of it gave me much to work with. that is why i have renamed this thread on Generating Said Video
Generating video is easy. Sycnronising it isn't.
Perhaps having a look at some of the items in the Parallax Object Library where people use the Propeller to overlay video on composite streams might be a place to start.
When I was a kid I built a genlock to lock an Apple ][ to a composite signal from the back of a tuner and put that into a basic video mixer with fade and wipe. From memory the video effects doo-dad was an old EA project. I recall buying the blank board from RCS by mail order. Anyway, by removing the colour burst oscillator on the Apple ][ it worked in a basic fashion to overlay B&W onto a composite stream, but not very well. As I grew up and met some broadcast engineers I started to understand why.
I also tried to build a Genlock for an old Philips VCR as I had the full service manual with schematics. It was then I started to understand why they used line-stores when genlocking video.
Good times.
Back in the day, before line stores were a twinkle in the eye of their ultimate developers, every source in a TV Studio was genlocked to the local SPG.
In the earliest cases, if they went to an OB, the whole Studio was genlocked to the SPG in the OB van.
To be really "seamless", this entailed setting up the van well in advance, opening up on that source on the day of the OB, & running till close down that way.
Alternatively, they just "went to black" & switched back to the local SPG.
(A quick loss of sync wasn't as obvious when "in black".)
A similar situation occurred, if using video direct off a broadband system.
Not long after that, the link system included a "reverse link" to send Studio blanking & syncs to the OB van, which then locked its SPG to that.(The timing difference from the link distance was undetectable by the viewer.)
That sorted things for OBs, not so much for stuff off the broadband.
Taping off the broadband, for later playback was the easiest answer, in most situations.
Line, & later, frame stores made such things a lot easier.