DVD video discs employ several levels of protection that are mainly controlled by the DVD Copy Control Association (DVD CCA) and a third-party company called Macrovision. This protection typically applies only to DVD-Video discs, not DVD-ROM software.

So, for example, copy protection might affect your ability to make backup copies of The Matrix, but it won't affect a DVD encyclopedia or other software application distributed on DVD-ROM discs.

Note that every one of these protection systems has been broken, so with a little extra expense or the correct software, you can defeat the protection and make copies of your DVDs either to other digital media (hard drive, DVD+RW, CD-R/RW, and so on) or analog media (such as a VHS or other tape format).

A lot of time and money are wasted on these protection schemes, which can't really foil the professional bootleggers willing to spend the time and money to work around them. But they can make it difficult for the average person to legitimately back up his expensive media.

The three main protection systems used with DVD-Video discs are:

• Regional Playback Control (RPC)

• Content Scrambling System (CSS)

• Analog Protection System (APS)

Regional Playback Control

Regional playback was designed to allow discs sold in specific geographical regions of the world to play only on players sold in those same regions. The idea was to allow a movie to be released at different times in different parts of the world and to prevent people from ordering discs from regions in which the movie had not been released yet.

Eight regions are defined in the RPC standard. Discs (and players) usually are identified by a small logo or label showing the region number superimposed on a world globe. Multiregion discs are possible, as are discs that are not region locked. If a disc plays in more than one region, it has more than one number on the globe. The regions are:

• Region Code 1. United States, Canada, U.S. Territories

• Region Code 2. Japan, Europe, South Africa, and the Middle East

• Region Code 3. Southeast Asia and East Asia

• Region Code 4. Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, and the Caribbean

• Region Code 5. Eastern Europe (east of Poland and the Balkans), Indian subcontinent, Africa, North Korea, and Mongolia

• Region Code 6. China and Tibet

• Region Code All. Special international or mobile venues, such as airplanes, cruise ships, and so on

The region code is embedded in the hardware of DVD video players. Most players are preset for a specific region and can't be changed. Some companies who sell the players modify them to play discs from all regions; these are called region-free or code-free players.

Some newer discs have an added region code enhancement (RCE) function that checks to see whether the player is configured for multiple or all regions and then, if it is, refuses to play. Most newer region-free modified players know how to query the disc first to circumvent this check as well.

DVD-ROM drives used in PCs originally did not have RPC in the hardware, placing that responsibility instead on the software used to play DVD video discs on the PC. The player software would usually lock the region code to the first disc that was played and then from that point on, play only discs from that region.

Reinstalling the software enabled the region code to be reset, and numerous patches were posted on Web sites to enable resetting the region code even without reinstalling the software. Because of the relative ease of defeating the region-coding restrictions with DVD-ROM drives, starting on January 1, 2000, all DVD-ROM drives were required to have RPC-II, which embeds the region coding directly into the drive.

RPC-II (or RPC-2) places the region lock in the drive, and not in the playing or MPEG-2 decoding software. You can set the region code in RPC-II drives up to five times total, which basically means you can change it up to four times after the initial setting.

Usually, the change can be made using the player software you are using, or you can download region change software from the drive manufacturer. Upon making the fourth change (which is the fifth setting), the drive is locked on the last region set.

Content Scramble System

The Content Scramble System (CSS) provides the main protection for DVD-Video discs. It wasn't until this protection was implemented that the Motion Picture Association of America (MPAA) agreed to release movies in the DVD format, which is the main reason the rollout of DVD had been significantly delayed.

CSS originally was developed by Matsushita (Panasonic) and is used to digitally scramble and encrypt the audio and video data on a DVD-Video disc. Descrambling requires a pair of 40-bit (5-byte) keys (numeric codes). One of the keys is unique to the disc, whereas the other is unique to the video title set (VTS file) being descrambled.

The disc and title keys are stored in the lead-in area of the disc in an encrypted form. The CSS scrambling and key writing are carried out during the glass mastering procedure, which is part of the disc manufacturing process. You can see this encryption in action if you put a DVD disc into a DVD-ROM drive on a PC, copy the files to your hard drive, and then try to view the files.

The files are usually called VTS_xx_yy.VOB (video object), where xx represents the title number and yy represents the section number. Typically, all the files for a given movie have the same title number and the movie is spread out among several 1GB or smaller files with different section numbers. These .VOB files contain both the encrypted video and audio streams for the movie interleaved together.

Other files with a .IFO extension contain information used by the DVD player to decode the video and audio streams in the .VOB files. If you copy the .VOB and .IFO files onto your hard drive and try to click or play the .VOB files directly, you either see and hear scrambled video and audio or receive an error message about playing copy-protected files.

This encryption is not a problem if you use a CSS-licensed player (either hardware or software) and play the files directly from the DVD disc. All DVD players, whether they are consumer standalone units or software players on your PC, have their own unique CSS unlock key assigned to them.

Every DVD video disc has 400 of these 5-byte keys stamped onto the disc in the lead-in area (which is not usually accessible by programs) on the DVD in encrypted form. The decryption routine in the player uses its unique code to retrieve and unencrypt the disc key, which is then used to retrieve and unencrypt the title keys.

CSS is essentially a three-level encryption that originally was thought to be very secure but has proven otherwise. In October 1999, a 16-year-old Norwegian programmer was able to extract the first key from one of the commercial PC-based players, which allowed him to very easily decrypt disc and title keys.

A now famous program called DeCSS was then written that can break the CSS protection on any DVD video title and save unencrypted .VOB files to a hard disk that can be played by any MPEG-2 decoder program. Needless to say, this utility (and others based on it) has been the cause of much concern in the movie industry and has caused many legal battles over the distribution and even links to this code on the Web. Do a search on DeCSS for some interesting legal reading.

As if that weren't enough, in March 2001, two MIT students published an incredibly short (only seven lines long!) and simple program that can unscramble CSS so quickly that a movie can essentially be unscrambled in real-time while it is playing. They wrote and demonstrated the code as part of a two-day seminar they conducted on the controversial Digital Millennium Copyright Act, illustrating how trivial the CSS protection really is.

Because of the failure of CSS, the DVD forum is now actively looking into other means of protection, especially including digital watermarks, which consists essentially of digital noise buried into the data stream, which is supposed to be invisible to normal viewing.

Unfortunately, when similar technology was applied to DIVX (the discontinued proprietary DVD standard), these watermarks caused a slight impairment of the image—a raindrop or bullet-hole effect could be seen by some in the picture. Watermarks also might require new equipment to play the discs.

Analog Protection System

APS (also called CopyGuard by Macrovision) is an analog protection system developed by Macrovision and is designed to prevent making VCR tapes of DVD-Video discs. APS requires codes to be added to the disc, as well as special modifications in the player.

APS starts with the creation or mastering of a DVD, where APS is enabled by setting predefined control codes in the recording. During playback in an APS-enabled (Macrovision-enabled) player, the digital-to-analog converter (DAC) chip inside the player adds the APS signals to the analog output signal being sent to the screen.

These additions to the signal are designed so that they are invisible when viewed on a television or monitor but cause copies made on most VCRs to appear distorted. Unfortunately, some TVs or other displays can react to the distortions added to create a less-than-optimum picture.

APS uses two signal modifications called automatic gain control and colorstripe. The automatic gain control process consists of pulses placed in the vertical scan interval of the video signal, which TVs can't detect but which cause dim and noisy pictures, loss of color, loss of video, tearing, and so on on a VCR.

This process has been used since 1985 on many prerecorded video tapes to prevent copying. The colorstripe process modifies colorburst information that is also transparent on television displays but produces lines across the picture when recorded on a VCR.

Note that many older players don't have the licensed Macrovision circuits and simply ignore the code to turn on the APS signal modifications. Also, various image stabilizer, enhancer, or copyguard decoder units are available that can plug in between the player and VCR to remove the APS copyguard signal and allow a perfect recording to be made.