DVD Encoding
DVD-Video can be encoded to either MPEG-1 or MPEG-2, as summarised in the table below:

Variable bit rate (VBR) encoding allows higher image quality at a lower average bit rate by using more data to encode those parts of a video sequence which are more complex and do not compress well. Using constant bit rate (CBR) encoding, the video data rate must be high enough to encode all the video well.

Early DVD-ROM drives used one of two strategies for delivering MPEG-2 video. Some used a technique called analogue overlay, also referred to as video overlay or simply overlay. Others employed the VGA-inlay approach, sometimes referred to as VideoInlay. Both methods display video in a window or at full screen, but they take different approaches. VideoInlay relies on the PC's graphics adapter to scale the video and output it to a monitor. Overlay boards, by contrast, provide their own hardware scaling and output the video themselves, overlaying it with graphics output passed through from the VGA card. With these boards, an included cable runs from the VGA connect of the display adapter to an input on the bracket of the decoder board.

The major drawback of the VGA-inlay approach is the load it places on a system. While pushing 30 frames of video per second might not saturate the PCI bus, it does keep bus utilisation high. When playing scenes encoded at a high bit rate, VGA-inlay boards can overwhelm older, slower display adapters with too much data, requiring a reduction in horizontal resolution to produce an acceptable picture.

Requiring a bit more work to install and configure than VGA-inlay boards, video-overlay boards demand less of a system and tolerate a wider variety of hardware. While video output may be less sharp than that displayed by VGA-inlay boards, the video-overlay approach has the advantage of being capable of decent performance with just about any video card.

The original audio encoding format specification for European DVD discs was MPEG-2 surround sound, creating a degree of confusion since Dolby Digital AC3 had become established as a mainstream format with the rest of the DVD world. The situation was clarified in January 1998 when the DVD Forum agreed on a dual standard which allowed both encoding formats.

The launch of DVD-Video has been severely impacted by technical issues, and not least those concerning encryption. DVD-Video players finally came to market in Japan in November 1996 and in the USA in March 1997. In Europe, the major launch was delayed until the autumn of 1998. 

DVD Encryption
By the end of 2000, there were six forms of DVD copy protection in use or planned:

• Analogue CPS (Macrovision): The general term is APS (Analogue Protection System). The system is designed to prevent copying onto consumer VCRs. The producer of the disc decides what amount of copy protection to enable and then pays Macrovision royalties accordingly. Just as with videotapes, some DVDs are Macrovision-protected and some aren't.
• CGMS: This is a 'serial' copy generation management system (SCMS) designed to prevent copies or copies of copies. The CGMS information is embedded in the outgoing video signal. For CGMS to work, the equipment making the copy must recognise and respect the CGMS.
• CSS: 'Content Scrambling System' is a form of data encryption to discourage reading media files directly from the disc. The system requires that DVD-ROM drives and video decoder hardware or software incorporate a decryption circuit that decodes data before displaying it.
• CPPM: 'Content Protection for Pre-recorded Media' replaces CSS for DVD-Audio. Keys are stored in the lead-in area, but there are no title keys in the sector headers. The disc key is replaced by an "album identifier."

• CPRM: The 'Content Protection for Recordable Media' mechanism - supported by all DVD recorders released after 1999 - ties a recording to the media on which it is recorded. It associates an encryption code with the unique 64-bit disc ID etched into the BCA of blank recordable DVDs when protected content is recorded onto the disc.
• DTCP: 'Digital Transmission Content Protection' is the frontrunner of a number of 'digital copy protection systems' (DCPS) under consideration. A draft proposal (called the 5CP, for 'five-company proposal') was made by Intel, Sony, Hitachi, Matsushita, and Toshiba in February 1998 which addresses digital connections between components via IEEE 1394. Content is marked with standard CGMS flags of 'copy never' or 'copy once'. Devices that are digitally connected, such as a DVD player and a digital TV, will exchange keys and authentication certificates to establish a channel. Products using DTCP are not expected before 2001 at the earliest.

Regional coding
Motion picture studios want to control the home release of movies in different countries because cinema releases aren't simultaneous (a movie may come out on video in the U.S. when it's just hitting screens in Europe). Also, studios sell distribution rights to different foreign distributors and would like to guarantee an exclusive market. Therefore they have required that the DVD standard include codes that can be used to prevent playback of certain discs in certain geographical regions. Each player is given a code for the region in which it's sold. The player will refuse to play discs that are not allowed in that region. This means that discs bought in one country may not play on players bought in another country.

Regional codes are entirely optional for the maker of a disc. Discs without codes will play on any player in any country. It's not an encryption system, it's just one byte of information on the disc, which recognises eight different DVD worldwide regions, that the player checks:

Region-2 coding standards proved more complicated to finalise than was originally expected, due to huge variations in censorship laws and the number of different languages spoken across the region, and was one of the main reasons for DVD taking so long to become established. It's impossible to include films coded for every country in Region-2 on a single disc. This led the DVDF to split the region into several sub-regions, and this, in turn, caused delays in the availability of Region-2 discs. By the autumn of 1998 barely a dozen Region-2 discs had been released, compared to the hundreds of titles available in the US. This situation led to many companies selling DVD players that had been reconfigured to play discs from any region.

With hindsight, the attempt at regional segregation was probably doomed to failure from the very start. The games console manufacturers (Nintendo, Sega and Sony) have been trying to stop owners from playing games imported from other countries for several years now. Generally, whenever such regional standards were implemented, it only took someone a few weeks to work out a way around it, whether it be a cartridge adapter or a modification to the machine itself. In real terms, all regional DVD coding has cost the DVD Forum a lot of money, delayed market up-take and allowed third-party companies to make a great deal of money bypassing it.

Ultimately, DVD will prevail as there's simply far too much heavyweight support behind it. In the US, even the die-hard LaserDisc collectors are being forced to adopt DVD as the movie studios cut down their LaserDisc production and ramp up their DVD output. With the increasing availability of DVD-ROM drives in notebook PCs and the availability of software-based MPEG-2 decoders capable of delivering significantly better results than older hardware-based solutions, it appears likely that DVD will make significant market inroads in the second half of 1998.

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