If you're going to use the 4051, you will need a video amp after it.

I actually tried it once. And was NOT happy with the results.
Like sinoteq said, the ON resistance is too high.
With a 1V p-p signal, I ended up with .8v p-p. Picture gets darker, and sync isn't great either.
Not to mention the Cross-Talk, ... really bad.

Maxim, has some very nice analog multiplexors and cross-point switches. Many are even less than 1 ohm ON resistance. No Amp required.

http://www.maxim-ic.com/products/switches/

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