All of the things in the world is consist of Timing and Space.
The video world also , but the timing here is the box,and the space is the Color space.

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The Fundamental for video understanding take the video signal as make up of two portion.
.1 the box(Timing define)
    the box is defined by the all kinds of sync signal in video.the horizontal sync , vertical sync is the most
base sync to define a video box of a signal.
.2 the content(Color Space Define)
    all of the video signal is consist of the R,G,B component color to make up a video content.

Later you will find that all kinds of the video siganl typs can be undrstanding by this two portion:
the box and content.
the Hsync Ysync and RGB

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.1 the box define:
The box seems as limited by Hsync and Ysync,then we get some composited sync types.
From Hs,Vs -> Cs(Hs,Vs in one signal line)-> GreenS(Sync on Green) ->YUV (Normally Sync on Y)-> YC (Sync on Y)-> CVBS

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.2 The Content:
The video's content is its color space

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referece:The Philips Trainning document.