Restrictions
DVD-Video has four complementary systems designed to restrict the DVD user in various ways: Macrovision, Content Scramble System (CSS), region codes, and disabled user operations (UOPs). There are also anti-ripping techniques intended to foil ripping software.
Content Scramble System
Many DVD-Video titles use Content Scramble System (CSS) encryption, which is intended to discourage people from copying the disc. Usually, users need to install software provided on the DVD or downloaded from the Internet such as WinDVD, PowerDVD, MPlayer, or VLC to be able to view the disc in a computer system.
CSS does not make it more difficult to copy the digital content, nor possible to distinguish between legal and illegal copies of a work, but it does restrict the playback software that may be used.
CSS has caused major problems for the inclusion of DVD players in any open source operating systems, since open source player implementations are not officially given access to the decryption keys or license to the patents involved in CSS. Proprietary software players were also difficult to find on some platforms. However, a successful effort has been made to write a decoder by reverse engineering, resulting in DeCSS. This has led to long-running legal battles and the arrest of some of those involved in creating or distributing the DeCSS code, through the use of the controversial U.S. Digital Millennium Copyright Act (DMCA), on the grounds that such software could also be used to facilitate unauthorized copying of the data on the discs.
The DMCA currently affects only the United States, however many other countries are signatories to the similar WIPO Treaty. In some countries it is not illegal to use de-scrambling software to bypass the DVD restrictions. A number of software programs have since appeared on the Web to view DVDs on a number of different platforms.
Other measures such as anti-ripping, as well as U.S. and non-U.S. copyright law, may be used to prevent making unauthorized copies of DVDs. CSS decrypting software, or ripping software, such as DVD Decrypter, AnyDVD, and DVD Shrink allows a disc to be copied to hard disk unscrambled. Some DeCSS applications also remove Macrovision, region codes, and disabled user operations (UOPs).
Anti-ripping
After DeCSS ripping software became available, companies developed techniques to introduce errors in DVD-Video discs that don't normally affect playback and navigation of a disc, but can cause problems in software that attempts to copy the entire disc. These approaches, which are not part of the official DVD-Video specification, include Sony ARccOS, Macrovision RipGuard, X-protect, ProtectDisc SecureBurn, Anaho , Fortium, and others. All of these methods have been circumvented (as might have been expected, since all standard DVD players naturally circumvent them to play and navigate the discs normally.)
Disabled user operations
Main article: User operation prohibition
DVD-Video allows the disc to specify whether or not the user may perform any operation, such as selecting a menu, skipping chapters, forwarding or rewinding—essentially any function on the remote control. This is known as User Operation Prohibitions, or Prohibited User Operations (UOPs or PUOs). Most DVD players respect these commands (e.g., by preventing skipping or fast-forwarding through a copyright message or an advertisement at the beginning of a disc). However, grey market players ignore UOPs and some DVD "re-authoring" software packages allow the user to produce a copy without these restrictions. The legality of these activities varies by jurisdiction and is the subject of debate.