Things around 10MHz are difficult - things above 100MHz are black art. This means you have to know your "physics", it's no longer "logic".
(1) You have a 74HC4067, haven't you? If not, why not?
(2) Anyhow this chip is more tricky than the 74HC4051, as it has no Vee option....
(3) Most likely your input signal is symmetric around ground. You should check this with an oscilloscop. To not loose the "negative" part you have to offset it, this can look a little bit like Figure 13 in the datasheet (cap plus voltage devider plus another cap) to "tunnel" it through the multiplexer.
(4) Also do a lot of decoupling, avoid ground loops!
(5) Doing video on a breadboard is never HiFi, best use PCBs with a lot of copper...