Extension of Analogue video:-
Analogue values are represented by a signal scaled to the value,
e.g. if a component of a scene is bright, the video signal recorded is
strong. If a component of a scene is dark, the video signal recorded is
weak. When copies are made of an analog signal, degradation is
introduced -- signals aren't recorded at exactly the same strength, and
false signals from the recording process can be introduced which distort the
signal.
Extension of Digital video:-
Digital means that each component of the scene is represented by a number
representing a discrete quantization, e.g. very bright components may be
represented by the number 255, and very dim components by 0. When digital
video is copied, it is nothing more than copying the set of number from one
medium to another. Since each number is discrete and copied exactly, there
is no degradation of the underlying image, and no noise is introduced that
can cause distortion.