Audio & Video mixer, spliter

[firewalker]

I want to transfer audio and video signal from a security camera through only one coaxial cable. I had seen somewhere such a device (consisted of two parts). One with two inputs for audio and video signal and one output for the mixed signal and one with one input for the mixed signal and two outputs for audio and video. I can't remember where... Any help? Even for a make it your self project. Thanks you very much.