Fair use rights are extremely complicated, and even copying entire works are not always seen as violating copyright.

Breaking encryption is specifically prohibited by the DMCA, but fair rights use predate it, and there are laws and court cases that allow certain types of copying for personal use in the US. Look up the Betamax time shifting case and the Home Audio Recording Act.

There is one section (1201) of the DMCA which disallows circumvention, but Section 1201c also states: (c) Other Rights, Etc., Not Affected.—

(1) Nothing in this section shall affect rights, remedies, limitations, or defenses to copyright infringement, including fair use, under this title

The anti-circumvention section of the DMCA has not been challenged on the basis of individual, non-commercial use, either for making backups or for format shifting. The media companies don't seem eager to bring this sort of thing to court either.
I'm not sure how the courts would rule on it.

Owning the physical media shouldn't really matter. This isn't just a discussion of dvds. If you buy the video online, you should still have the right to view it as you see fit, even if that means breaking the drm that is added so you can change the format to play on all your media players.