Heather, the definition of a "short portion" was purposefully left vague.  I'm pasting in below the applicable section from the Recommendation of the Register of Copyrights that was accepted by the Librarian of Congress.  It's on the web at http://www.copyright.gov/1201/2010/initialed-registers-recommendation-june-11-2010.pdf and this section starts on page 53.

Hope that helps!

c. The meaning of a “portion” of a work
The proponents of classes of works related to DVDs relied only on activities involving the
use of portions of DVDs192 “for the purpose of extracting clips for inclusion in noncommercial
videos that do not infringe copyright,”193 or “for the purpose of making compilations of portions
of those works for educational use in the classroom by media studies or film professors.”194 The
Copyright Office sought clarification for the contours of a “portion” in questions after the
hearing, inquiring whether specific quantitative limitations would be advisable.195 Proponents and
opponents both generally opposed quantifying a “portion” in relation to a maximum length or
percentage. Although delineation of what amount or percentage of a work would, at its outer
limits, constitute a “portion” was generally said to be impossible, all of the specific evidence
introduced into the record to illustrate vids or documentaries demonstrate that, generally, a
relatively small percentage (quantitatively) of the motion picture is needed for the creation of a
vid.196 The Register agrees that the use of some portion of a motion picture for a transformative purpose may qualify as a fair use.
The opposition to any form of delineation of a portion in regard to time-length or
percentage of the overall work was, broadly speaking, two-fold. First, proponents argued that a
precise limit would raise a host of questions, such as, what would the percentage specifically
apply to: the contents of a DVD or a component work on the DVD? Second, both proponents and
opponents stated that since the amount of the use was only one factor in the fair use analysis,
delineating a particular amount in an exemption to the prohibition on circumvention might
mislead the public. On one hand, opponents argued that the public might interpret the exemption
to indicate that any use of such a “portion” is necessarily noninfringing. On the other hand,
proponents argued that some uses in excess of the articulation of a “portion” might be a fair use
under the totality of the fair use analysis, but would be precluded by the exemption. While it was
not the Copyright Office’s intention to suggest that any temporal limitation set forth in the
definition of the class should be interpreted as drawing the line between a fair use and an unfair
use, the Register recognizes that any attempt to determine precisely how large an excerpted
portion could be without violating the prohibition on circumvention would be problematic. An
amount that might be reasonable in one context might be excessive in another. Moreover, a
regulation defining how large an excerpted portion of a work could be for purposes of the
exemption from the prohibition on circumvention could well mislead the public into a false belief
that the regulation was, for all practical purposes, defining the quantitative limits of fair use.
Nevertheless, the Register concludes that some characterization of the quantitative amount
of the use for purposes of criticism or comment is appropriate. No commenter or witness has
persuasively argued that designation of a class of works is warranted in order to permit the use of
extensive excerpts of motion pictures. Virtually all of the evidence of noninfringing uses of
motion pictures for criticism or comment has involved short portions of motion pictures in order
to make a pedagogical point or to use a work for criticism or comment in a documentary film or
noncommercial vid. There was concern expressed that qualification of a “portion” in some way
might raise questions about the cumulative amount of a work used in a transformative work, or
the cumulative amount used within a semester of classes. While these concerns have some merit,
the Register finds that the benefit of some qualification of the term “portion”outweighs the costs.
The inclusion of the phrase “short portions of the works” in the description of the class will make
it clearer that a case that extensive use of a motion picture is a noninfringing use has not been
established in the record, and that such uses disqualify a user from the benefit of the designation
of this class of works. Likewise, if a film class focused on a particular film over the course of a
semester, the fact that most (or all) of the work was cumulatively used during the semester would
not prevent the application of the exemption to short portions incorporated into a number of
compilations of clips for use in individual classes.
The use of the phrase “short portions of the works” highlights the evidentiary record that
forms the basis of this recommendation. The proponents’ justification for the need for designating
a class of works has not established that relief is needed to permit circumvention for the purpose
of making more than a short portion of a work. This is not to suggest that the use of a long portion
cannot be a noninfringing use in a particular circumstance. However, noninfringing uses may be
accomplished in various ways without circumvention, as the record in this rulemaking
demonstrates. The harm to copyright owners’ interests that could result from a generalized
perception that any amount, or large portions, of a motion picture can be reproduced through
circumvention warrants a balancing of the interests in this case. Those interests can best be
balanced by limiting the class to permit the use of short portions of motion pictures.

Sarah E. McCleskey
Head of Access Services
Acting Director, Film and Media Library
112 Axinn Library
Hofstra University
Hempstead, NY 11549-1230
[log in to unmask]
516-463-5076 (o)
516-463-4309 (f)

-----Original Message-----
From: ARLIS/NA List [mailto:[log in to unmask]] On Behalf Of Gendron, Heather Hope
Sent: Tuesday, July 27, 2010 4:17 PM
To: [log in to unmask]

Subject: Re: [ARLIS-L] [District Dispatch] Librarian of Congress heeds LCA’s requests, broadens exceptions to Digital Millennium Copyright Act

This is a great move forward.  Does anyone know how a "clip" is defined here?

Heather Gendron
Art Librarian
Sloane Art Library
UNC Chapel Hill
102 Hanes Art Center
CB#3405
Chapel Hill, NC 27599-3405
Phone: 919.962.1061
Homepage: http://www.lib.unc.edu/art/index.html
Facebook: http://www.facebook.com/pages/Chapel-Hill-NC/Sloane-Art-Library/113315877644



-----Original Message-----
From: ARLIS/NA List [mailto:[log in to unmask]] On Behalf Of Lawson, Roger
Sent: Tuesday, July 27, 2010 1:44 PM
To: [log in to unmask]
Subject: [ARLIS-L] FW: [District Dispatch] Librarian of Congress heeds LCA’s requests, broadens exceptions to Digital Millennium Copyright Act

Forwarded on behalf of the ARLIS/NA Public Policy Committee.

Roger C. Lawson
Administrative Librarian
National Gallery of Art
Washington, DC

-----Original Message-----
[District Dispatch] Librarian of Congress heeds LCA’s requests, broadens exceptions to Digital Millennium Copyright Act


> To: [log in to unmask]
> From: <[log in to unmask]>
> Date: Tue, 27 Jul 2010 10:21:26 -0500 (CDT)
> Subject: [District Dispatch] Librarian of Congress heeds LCA’s
 requests, broadens exceptions to Digital Millennium Copyright Act
>
> FULL POST: http://bit.ly/981Nea
--
District Dispatch has posted a new item, 'Librarian of Congress heeds LCA’s requests, broadens exceptions to Digital Millennium Copyright Act’

The following is a release issued today by the Library Copyright Alliance.

For Immediate Release:
July 27, 2010

LCA applauds Librarian of Congress for broadening exceptions to Section 1201 of the Digital Millennium Copyright Act

The Library Copyright Alliance (LCA) applauds yesterday’s decision issued by the Librarian of Congress to significantly broaden the exemption for the creation of film clip compilations for classroom and educational use to all college and university faculty, regardless of academic discipline.

According to Section 1201 (a) (1) of the Digital Millennium Copyright Act (DMCA), the Librarian of Congress is allowed once every three years to adopt exceptions to the anti-circumvention provisions that place technological protections on copyrighted works. In this latest round of exemptions, the Librarian of Congress, acting on the Register of Copyright’s recommendations, ruled in accordance to the requests
(http://www.librarycopyrightalliance.org/submissions/domestic/circumvention.shtml)
made by Library Copyright Alliance members – the American Library Association (ALA), the Association of College and Research Libraries, and the Association of Research Libraries (ARL).

The DMCA established a provision that prohibited disabling passwords, scrambling systems, or other technological protection measures without the prior authorization of the rightsholder. At the same time, the DMCA also established a mechanism to periodically check if this provision prevented users of copyrighted works from making lawful uses of works, such as fair uses.

As a result of yesterday’s decision on exemptions, college and university faculty in all disciplines can lawfully circumvent the Content Scrambling System (CSS) typically used on DVDs for teaching purposes. Prior to this rulemaking, only faculty who taught film or media studies could exercise such an exemption. The LCA in its comments demonstrated that the use of film clips for educational purposes is in fact common and valuable in many disciplines. In today’s classroom, the inclusion of media resources is standard. The new rule also applies to university film and media students. In addition, circumvention can be performed for the incorporation of short portions into new works for the purpose of criticism or comment, not just the assembly of clip compilations for in-class screening purposes. The Librarian further expanded this exemption to documentary filmmaking and noncommercial videos.

LCA also is gratified by the Librarian of Congress’s renewal of the exemption to circumvent protections that block the read-aloud/screen-reader function on e-books.

For a full report on this and other exemptions, see the U.S. Copyright website (http://www.copyright.gov/1201/).

###

The Library Copyright Alliance (LCA) consists of three major library associations—the American Library Association, the Association of Research Libraries, and the Association of College and Research Libraries. These three associations collectively represent over 300,000 information professionals and thousands of libraries of all kinds throughout the United States and Canada http://librarycopyrightalliance.org/.

You may view the latest post at
http://www.wo.ala.org/districtdispatch/?p=5177

You received this e-mail because you asked to be notified when new updates are posted.

Best regards,
Jacob Roberts
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