Video Overlay for SMPTE 292m

Video Overlay for SMPTE 292m

I'm trying to find a way to add an overlay to SMPTE 292 video as it is
being transmitted.
I've never really worked with video so I'm trying to avoid making
assumptions that will ruin my day in the future.
The system is essentially like this:
A device(let's say a laptop) generates the video and sends it out on a
wire. Another device is connected at the end(a monitor) that shows the
video. The device I'm looking at making will cut into that wire and
attempt to add an overlay to the video. To be clear, I don't have access
to the source device or the receiving device, so I'll just be playing man
in the middle and manipulating the video after it has been sent out.
Now, in my mind the easiest way to do this would be to read in one frame
of the video, add on the overlay, and send the frame out.
Is this an overly naive approach? The things I've read so far seem to
indicate that video is more complicated than that, and I can understand
that on the lowest levels that it can be more complicated, but are there
software libraries that can be used to accomplish this? I'd prefer
libraries for any high level language like C++, Java, C#, etc but it
doesn't really make a difference.
Also, is there better terminology that I can use to learn more about this?
My only search terms right now are video and overlay which are pretty
ambiguous.