The Federal Copyright Act (Title 17, US code) governs how copyrighted materials may be used. Neither the rental nor the purchase of a DVD carries with it the right to be shown outside the home, unless the site where the video is shown is properly licensed for exhibition. This compliance requirement applies to colleges and universities regardless of whether admission is charged, or whether the institution is commercial or non-profit. Public showings of films without an appropriate license put an institution at risk.
There is an exemption in the code, Section 110(1) which states that it is not an infringement of copyright when a video is displayed by instructors in the course of face-to-face teaching activities of a nonprofit educational institution, in a classroom or similar place devoted to instruction. However, when the University advertises programs as free and open to the public, and invites anyone to attend, this negates application of the classroom exemption.
Some films held by the Clemson University Libraries were purchased with public performance rights, but most were not; public performance rights add significantly to the cost of a film, and most films in the collections are used in ways that don't necessitate securing a public performance license.
Can I show a video in a class? Yes. This is the face-to-face teaching exemption permitted by Section 110(1) of the Copyright Law .
Can I break encryption to make video clips? Yes. Exemption 1201(a)(1) allows college and university professors to circumvent encryption to make clips of short portions of a work for educational use.
Can I show a video at a special event? You will need to secure public performance rights to show a video in a setting outside the classroom (such as a film series). This requires planning ahead, and, frequently, a substantial fee.
Can I tape a video off television and show it in class? Yes, but there are Congressional guidelines saying you can only retain it for 45 days as a teaching tool (there can be some flexibility with this). It's best to try to acquire the content from a commercial vendor.