> Most modern systems (and computers) are sending digital signals where entire frames need to be constructed and reconstructed in a buffer before they can be displayed.

HDMI and DVI-D are a digital representation of a tv signal --- there's all the blanking and porches and stuff (audio data is often interleaved into the blanking periods). You could process that in realtime, even though most displays don't (including CRT HDTVs; I trust your maybe one doesn't).