KEI has a page that summarizes the minimum terms of protection for copyright and related rights in multilateral treaties. The most binding constraints are those included in the WTO TRIPS Agreement. Those constraints are as follows:
Most literary and artistic works protected by copyright under the Berne would have a minimum copyright term calculated on the basis of the life of the author plus 50 years.
For cinematographic works, or anonymous or pseudonymous works, the minimum term is normally 50 years after a work is made available to the public.
For photographs or a work of applied art, the TRIPS and the Berne have a 25 year minimum term.
For works where the term of protection is calculated on a basis other than the life of a natural person, such as a work-for-hire, the minimum term is 50 years from end of the year of the publication or making of the work.
For all of these works, there can be no requirement for formalities during the period of the minimum term.
Under TRIPS, the minimum term of protection for performers, or producers of phonograms is 50 years from the performance or the fixation of the recording. Countries may require formalities for these rights. The Rome has an elaboration on the type of formalities that are appropriate.
For countries that recognize the broadcasters right (the US and many countries that have not signed the Rome do not), the TRIPS minimum protection is 20 years, and there are no restrictions on formalities.