Possible to sync on external H- and V-sync?

Hi,

I'm currently working on a CRT chassis and would like to implement my own OSD. For that I'd like to either use an Arduino or ESP8266. Instead of generating the H- and V-sync I'd like to sync on the existing signals and generate the characters and use one of the color channels to blank my RGB IC on my CRT chassis.

Do you think that would be possible?