There were that chips to create OSD that can do pretty neat gfx tricks in low resolution and compose the data into existing video signal, while requiring really little computational power.

When projecting a display, please think in terms 24x72 characters which is about the smallest "common" terminal screen size (25x80, IBM standard preferred)) Smallest readable font I know is 5x5px plus 1px break (a hack to leave every 6th pixel blank to save cycles i.e. for IO is possible then)
Also note in 1bit color depth, 24x72x5x5/8=5400 bytes of Video RAM at 120x360 resolution.

By the way, which input do the links describe? The "Composite video"? Because standard antenna input is more complex than that (the above is overlaid with a carrier wave).