Digital Millenium Copyright Act (DMCA)
It is not permissable to "rip" a DVD and disable copyright protection measures. Refer to 17 U.S.C. § 1201 : US Code - Section 1201
Additional Violations. — (1) No person shall manufacture, import, offer to the public, provide, or otherwise traffic in any technology, product, service, device, component, or part thereof, that —
(A) is primarily designed or produced for the purpose of circumventing protection afforded by a technological measure that effectively protects a right of a copyright owner under this title in a work or a portion thereof;
(B) has only limited commercially significant purpose or use other than to circumvent protection afforded by a technological measure that effectively protects a right of a copyright owner under this title in a work or a portion thereof; or
(C) is marketed by that person or another acting in concert with that person with that person's knowledge for use in circumventing protection afforded by a technological measure that effectively protects a right of a copyright owner under this title in a work or a portion thereof.
(2) As used in this subsection —
(A) to “circumvent protection afforded by a technological measure” means avoiding, bypassing, removing, deactivating, or otherwise impairing a technological measure; and
(B) a technological measure “effectively protects a right of a copyright owner under this title” if the measure, in the ordinary course of its operation, prevents, restricts, or otherwise limits the exercise of a right of a copyright owner under this title.
Showing Videos in Class
Copyright on videos and DVD's does not grant permission for public performance or public showing, unless the site where the video is used is properly licensed for copyright compliant exhibition.
That said, the Librarian of Congress may issue exemptions to Section 1201(a)(1) of the Digital Millennium Copyright Act (DMCA). In July of 2010, an exemption was announced to the following relevant class of work:
"Under the United States Copyright Act, Title 17 of the United States Code, movies may be shown without a separate license in the home to “a normal circle of family and its social acquaintances” because such showings are not considered public. However, only the copyright holder has the right to “perform” a movie outside the sphere of family and friends. A "public performance" is a showing of a motion picture or other program outside of the home. This legal requirement is the same whether the movie or program has been purchased, rented, or borrowed; buying the movie does not grant one the right to perform it in public. Both for-profit organizations and non-profit institutions must secure a public performance license, regardless of whether an admission fee is charged."
If you want to host the public performance of a movie - outside of class - you must obtain a license to do so. Most licenses can be obtained from the Motion Picture Licensing Corporation (MPLC), an "international, independent copyright licensing agency authorized by motion picture copyright holders, such as studios and producers, to issue the MPLC Umbrella License for the public performance of copyrighted motion pictures and other programs."
Obtaining Performance Rights
Performance rights organizations (PRO's) provide intermediary functions, particularly royalty collection, between copyright holders and parties who wish to use copyrighted works publicly in locations such as shopping and dining venues. Below are links to the most prominent US PRO's.
VHS to DVD
It is not OK to copy published works from VHS to DVD. Copyright law does not allow for the transfer of formats (e.g. tape to DVD) without permission of the copyright holder, EXCEPT for the limited provisions of Section 108 of the copyright law (see the Section 108 Working Group website for details).
Section 108 allows replacement copies to be made by libraries and archives in cases where a title is at physical risk of deterioration, or is in an obsolete format, AND the title is not available for replacement at fair market prices. There are strict stipulations about the use and users of such replacement copies; most notably, the copy must be used within the confines of the library only.
Individuals are prevented by copyright from making DVD copies of copyrighted tapes that they own. Use of such copies in the classroom is most definitely illegal.
Items obtained and/or purchased on iTunes are subject to the same copyright laws as those applied to any other audio/visual format, unless otherwise specified by the creator and/or poster. In this regard, think of iTunes not as a different iteration of content with different sharing rules, but simply as content delivered in a different physicalformat requiring a different playback device.
Ex: a VHS, DVD and/or iTunes .mp4 copy of The Godfather are all physical manifestations of the same creative work; that creative work (The Godfather) being the item to which copyright is actually applied.
Note: just as it is not legal to copy a VHS to a DVD (other than for preservation purposes, per 17 USC § 108), it is not ok to burn an iTunes .mp4 file to a DVD or to convert the file to another format.
According to Section 6(C) of the YouTube Terms of Service, as a YouTube content provider:
... retain all of your ownership rights in your Content. However, by submitting Content to YouTube, you hereby grant YouTube a worldwide, non-exclusive, royalty-free, sublicenseable and transferable license to use, reproduce, distribute, prepare derivative works of, display, and perform the Content... You also hereby grant each user of the Service a non-exclusive license to access your Content through the Service, and to use, reproduce, distribute, display and perform such Content as permitted through the functionality of the Service and under these Terms of Service.
In translation: YouTube content may be freely used, reproduced and "performed" publicly, but only within the YouTube environment. You cannot legally download, copy or in anyway pull content off the YouTube site; you cannot create physical derivatives of a YouTube video (i.e. burn to a DVD) or otherwise take posted content off-line.