Simple way to isolate video signal
For composite video you'd need a wideband transformer, as the signal has quite a bit of low frequency information.

Well, I simply googled "composite video transformer" and came up with this.

EDIT:

Composite video bandwidth seems limited to less than 10MHz so I can reuse the research I did to select a SPDIF transformer. So, Murata DA102.



Note transformers don't care about the 75R impedance. They do introcude a discontinuity though, so the length of transmission like from the transformer to the receiver should be kept short.