Well ideally it would be twenty five years from date of publication with extensions of five years upon re-release, up to three times. Meaning you could, at most

Well ideally it would be twenty five years from date of publication with extensions of five years upon re-release, up to three times. Meaning you could, at most, get forty years, but only if you re-released the media in question before the original copyright term or the extensions ends. This means that only the most enduring media will likely get forty full years of protection. Meaning that, had a film come out in 1984 and not been re-released in any form since it's original theatrical run from 1984 to 1985, it's copyright protection would have ended in 2009. But if it got a VHS release in 1988, a DVD release in 2002, and a Blu-Ray release in 2009, it's copyright wouldn't have expired until just this year. To make this work, making sure sub-licensing and syndication do not count as releases (the show appearing on a television channel or a third party streaming service for example) would close some of the loopholes. This would also mean that for the full forty years of protection there has to have been physical media created, providing a protection that the data can't be arbitrarily revoked.