Filter power supply for video signals
The Efields of the SMPS will couple, thru the AIR, into the video circuits. 

Plan to shield the SMPS. Experiment with this, to be sure shields are needed.

Or shield the video circuits from the MCU and the SMPS?

Also you probably need a serious PI input filter, or common-mode choke, into the SMPS, to reduce trash currents that will find your video SOURCE and enter thru the 75 ohm coaxes.

And, as you suggested, use an LC filter between the SMPS output and your video circuits.

Using this mindset (placing inductors in ALL paths out of the SMPS including GND/RTN pins), I've achieved cleaner than 12 bit systems for avionics (air-air missile detection via IR).