Managing Your Work Environment > Setting Preferences > Timeline Preferences >
Transitions

Use these preferences when creating transitions.

(a) Transition Alignment box(b) Curve Type box(c) Dissolve Render Mode box

Transition Alignment box
  Set the default alignment for dissolves, wipes, axis, and custom transitions to Centred, From Cut, or Up To Cut.
Dissolve Duration field
  Set the default duration for dissolves.
Curve Type box
  Select Bézier or linear as the default curve type for dissolves.
Dissolve Render Mode box
  Use to set the default rendering type for dissolves created in the timeline. Note that you can change this when you create a dissolve.