you want something like this. it has a built in multiplexer so you can add extra cameras if you want and motion detection which reduces your storage requirements hugely. the motion detection is built into the software rather than being at the camera end so no extra hardware needed.
if the field of view of your camera includes things which tend to be in motion a lot (e.g. tree branches) then check if the system you get allows you to mask certain areas against motion detection. if not you'll end up with constant recording which is a huge drain on resources and makes it very difficult to identify incidents, you only want to record when something is actually happening.
http://www.henrys.co.uk/cctv/multicam.htm
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