Is it possible to set a global transition effect for all frames instead of specifying the effect again for each frame?
Short answer: no.
The longer answer is that the way the
frame environment is set up in
beamer deliberately resets the transitions and buries this deeply within the code. That reflects the original author's position that transitions should be used sparingly and for single frames only. Altering this behaviour would require a significant rewrite of parts of
As a workaround similar to the one provided in Is it possible to define transduration for frames created with allowframebreaks?, you can add the transition effect to the
background canvas template so that it is reactivated automatically after each reset:
% Add global transition effect \transfade
An other way is to use impressive for your presentations. This software allow you to add transition effect between pages of your pdf.