Returns the value from the siTimeControlExtrapolationType
enum that corresponds to how a clip contributes to the animation
before the frames on which it is defined.
On the Time Control property editor, this appears on the
Extrapolation tab under Before as the Type parameter. The value of
this property determines what kind of value will be considered for
the ExtrapolationBeforeValue. For example, if
ExtrapolationBeforeType is set to 2 ('Cycle'), then the
ExtrapolationBeforeValue will read from the 'Cycles' parameter.