If you have built a video transmitter a 40KHz oscillator should be a piece of cake. What do you need a micro controller for?

When the IR receiver receives an input, that could then start the 40KHz oscillator via transistor to an IR LED to extend the range.

Again, if you have built the video components, why do you have to ask about IR?

Or, have you got a bunch of stuff pre-built and ran a few cables?