In 2010 exemptions were made to the anti-circumvention provisions of the Digital Millenium Copyright Act which allows professors and students to be able to decrypt and excerpt copyrighted video content for lectures and class projects as long as they are non-commercial. Check out the Recut Reframe Recycle website of the Center for Media & Social Impact at American University for examples.
You can read more about inserting short clips from copyrighted works into lectures here:
http://www.insidehighered.com/news/2010/07/28/copyright