Access Time
Amount of time it takes a CD-ROM or DVD drive to find and display the requested information. Although specified widely, access times must be used with care because there is no measuring standard. It is generally regarded to include radial positioning time (the head moves to the appropriate track), plus settling time (stops vibrating), plus latency (wait for beginning of block with the wanted data), all of which take much more time than the final read and display step. Top

Aspect Ratio
The height to width ratio in PC and TV monitors. In DVD Video, the video display frame can have different rectangular shapes, determined by its recording aspect ratio (4:3 or 16:9). DVD Video also offers panoramic and letter-box display formats (options). Obviously, not all TV sets offer a 'wide screen' option, and viewing a film using the improper aspect ratio leaves dark (unused) areas or bands in the screen. Top

CSS (Content Scrambling System), Macrovision
Implemented by the DVD Consortium, implements the Analog Protection System (APS) and the Data Encryption Standard (DES), to protect the contents of a DVD Video title from being downloaded or dumped and reused. One major option that implements the APS is Macrovision (to degrade the analog stream being copied). The technology involves special DES algorithms to scramble critical sectors of the DVD Video, creation of special 'keys' for guiding the descrambling process by chips in the DVD-player, and use of an APS to prevent an analog signal be diverted or captured 'clear' or at high quality (before it reaches the monitor or TV screen). Matsushita, developers of the CSS, license it for free. Macrovision licenses its APS product for free to hardware manufacturers, and requires royalties from content publishers. Top

Dolby AC3
This is Dolby Digital audio, using AC-3 compression (from a source PCM stream), sampled at 48 kHz, and 16 bits. This is one of the digital audio formats that are included in the DVD Video specifications required for DVD Video titles for NTSC countries. It involves 1 to 5.1 channel surround-sound, and is of higher quality than the CD-Digital Audio. Top

DTS
Dolby Tru-Surround. All DVD players are DTS compatible. They pass the digital audio information onto the audio amplifier which then decodes it. If your DVD player has a DTS decoder built in then this conversion is done inside the DVD player and is output as 6 seperate analogue channels which are then passed to the amplifying equipment. Top

Capacity Of A DVD
The DVD capacities for 12cm and the much forgotten 8cm disc, which involves single and double-layer, as well as single and double sided discs, are shown in the following list below.

• Single Side, Single Layer (aka DVD-5) 8cm=1.4Gb 12cm=4.7Gb
• Single Side, Double Layer (aka DVD-9) 8cm=2.6Gb 12cm=8.5Gb
• Double Side, Single Layer (aka DVD-10) 8cm=2.9Gb 12cm=9.4Gb
• Double Side, Double Layer (aka DVD-18) 8cm=5.3Gb 12cm=17Gb

Laser
Light Amplification by Stimulated Emission of Radiation was demonstrated about half a century ago, with an original ruby laser. Today, lasers are everywhere to suit many diverse technologies and applications. Tests of blue, blue- green, and blue-purple lasers of higher precision, have been carried out which will make possible higher density optical discs. Ultraviolet lasers produce heat and require cooling, just as do the barely visible violet Krypton gas lasers. Cooling and size requirements are key to the implementation of a laser to optical disc technologies. Mastering plants use sophisticated Laser Beam Recorders with low wavelength (@350nm) ultraviolet or argon lasers. Top

Linear PCM
Linear Pulse Control Modulation is a string of sampling codes in a digital audio file, a code for each sample. Linear PCM does not involve any compression techniques, and can be used in DVD as it is, or as base for a compressed format. Top

Mounting
Mounting is the term used for the time taken for a player to recognise what type of disc has been inserted. Mounting times can vary tremendously depending on the type of media on the disc. Mounting times of under 1 second are commonplace for audio CD's in dedicated CD players but DVD's may take up to 20 seconds to mount and start playing. Top

MPEG
A Codec adopted by ISO's Motion Pictures Expert Group for compression and playback of full motion video and audio streams. Often referred to as 'MPEG video.' MPEG-1 is now an open standard which establishes the structure for a standard MPEG file, and specifies a transfer rate of 1.5Mb/sec, with a resolution of 352x240 at 30 fps. Incidentally, CD-I uses MPEG-1, and VCD was promoted as the first MPEG1 optical disc for multiple platforms. DVD implements 'hardware' MPEG 2 and offers higher resolution, uniform quality, different aspect ratios, and more features than MPEG 1. MPEG 2 and AC 3 Audio do the decoding together. In some circles, hardware MPEG 2 is still considered a temporary solution in the wait for a software solution (current software decoders require powerful CPUs, ample RAM, and MMx at least). Top

MPEG Audio
This is a digital multichannel audio format, which uses a source PCM stream to compress it at a sample rate of 48kHz, sample size 16 bits. DVD supports MPEG 1 and MPEG 2 audio formats: 2.0, 5.1, or 7.1 channel audio, at 48 kHz/sec, or Dolby Digital AC 3, 5.1 channel audio at 48 Khz/sec, as well as 16 to 24 bit Linear Pulse Control Modulation (LPCM), at 48 or 96 KHz/sec. Top

NTSC
The National Television Standards Committee supports the NTSC signal and display technology used in the TV industries of North America, Japan, and a few other countries. It specifies 525 lines/screen, and 29-30 frames/sec. Top

PAL
Phase Alternation Line. A television standard that is used by European, Asian and some Latin American Countries. It specifies 768 pixels/line, 576 lines/screen and 25 frames/sec. Top

PCM
Pulse Code Modulation is used to sample analog audio into digital code (generally, 8000 samples/sec), and to structure the analog signal that is produced by the digital-analogue converter of a CD-Audio player. The digital audio string is often referred to as Linear PCM, or also as just PCM. Top

Pits
During optical encoding, pulses of a high power laser beam 'burn' microscopic 'pits' on the recording layer. The untouched spaces between such pits are called 'lands.' During the read process, the laser light focuses on the spinning spiral track, and since the pits reflect light less intensely, the read head detects the changes in reflectivity, and those transitions are processed as is to produce a binary data stream. In CD-ROM, the track pitch is 1.6 microns, and the pits are .83 microns wide. In DVD, the track pitch is 0.74 microns, and the pits are 0.4 microns wide. Maximum pit lengths are 10 times pit width. Top

Pixel
A Picture Element, used mainly in graphics and video circles, is the smallest unit of display that can be given colour and intensity values or codes. The larger the number of bits per pixel, the higher the range of colors that can be displayed. Top

Protective Coating
Optical discs are given a clear plastic or lacquer coat that protects the metallic layer. Even with this coating, small scratches, pressure, dirt and other markings can make the disc unreadable. It is only designed to protect the disc under careful handling conditions. The coating also prevents air from reaching and oxidizing the metallized layer which would render the disc unreadable. Top

RCE
Regional Coding Enhancement allows the disc to detect if a player is region specific (as required by the CSS licensing agreement), or if it has been altered to be "region free" (i.e. region 0). If the player is "region free" the RCE will not allow the disc to be played. It will instead display a message on the television advising the consumer that the machine is not authorized to play the DVD in question.

• Current RCE Titles (Affects Region 1 Only)
  • 6th Day
  • All The Pretty Horses
  • The Brothers
  • Charlie's Angels
  • Finding Forester
  • Joe Dirto Hollow Man
  • A Knight's Tale
  • The Patriot
  • Saving Silverman
  • Snatch
  • South Park : Chefs Experience
  • South Park : Xmas in South Park
  • Thomas Tank & Magic Railroad
  • Tomcats
  • Urban Legend Final Cut
• 
  (Last Updated 25/10/01) Top

Region Code Areas
Also referred to as Country Codes, or Zone Locks, these are optional codes that the movie industry imposed on DVD-Video specifications. Players are generally coded by region, and these players will not play DVDs coded for a different region. DVDs with no regional codes will be played by any DVD player. Players that are auto or selectable Multi-Region (rather than Region Free) are reputed to play any DVD from any region.

Region code areas are divided into 6 (at the moment) areas throughout the world. These are

• Region 1 - Canada, U.S., U.S. Territories
• Region 2 - Japan, Europe, South Africa, Middle East (including Egypt)
• Region 3 - Southeast Asia, East Asia (including Hong Kong, Taiwan)
• Region 4 - Australia, New Zealand, Pacific Islands, Central America, Mexico, S. America, Caribbean
• Region 5 - Former Soviet Union, Indian subcontinent, Africa (Also N. Korea, Mongolia)
• Region 6 - China

Sampling
Sampling is part of analog to digital conversion. Essentially, the analog signal is sampled at an specific rate and quantized, which means a numerical value is matched to each sample, and that value is convened to binary code. Although the frequency of sampling is important for continuity, the size of the sample (in bits) is important for depth of quality. Top

Scart Socket
Scart sockets and their respective leads are used to make a quick and effective connection between AV equipment and TV's/Video's. They have 21 pins in total and their respective jobs are listed thus:

1. Audio Output (1) Right channel 0.5V RMS
2. Audio Input (1) Right Channel 0.5V RMS
3. Audio Output (2) Left Channel 0.5V RMS
4. GND (Audio)
5. GND
6. Audio Input (2) Left Channel 0.5V RMS
7. RGB Input, BLUE (B)
8. Switch Signal Video (status)
9. GND
10. Clock Signals
11. RGB Input, GREEN (G)
12. Remote Control
13. GND
14. GND Switch Signal RGB
15. RGB Input, RED (R)
16. Switch Signal RGB
17. GND (Video)
18. GND
19. Video Output 1V p-p
20. Video Input 1V p-p
21. Shield

Title (DVD)
In DVD Video, a title is an independent or self-contained program, usually a whole movie or TV program episode. A DVD can contain more than one title. Obviously the amount of titles on any given DVD depends on the size of the titles. Top

TOC
Table Of Contents generally implies a list of the files and addresses of a CD-ROM application. The TOC is in the lead-in area of a CD, and can hold 99 addresses (which is therefore the number of tracks that a CD can have). In current multisession applications, each session involves its own table of contents and the application scans the disc and begins to read the last table of contents first. Top

Variable Bit Rate
DVD specifies a Constant Linear Velocity (CLV) of 3.49 m/s, giving a transfer rate of 11.08 Mbits/sec, although 9.8 Mbits/see is the top usable limit. But MPEG-2 implements variable bit rate encoding (often called variable rate bitstream encoding), because it helps to optimize quality in the program video stream while catering for maximum compression. Essentially, the sequences with high level of motion are allowed higher data rates than the sequences with low levels of motion. It uses track buffers, intermittent reads, and even a complete double pass process to achieve a high quality data stream within the allocated bandwidth (variable bit rate decoding for the video, the audio streams, and the subtitles). Obviously, the average bit rate in DVD-Video depends on the complexity of the video application, and can be anywhere up to the top limit. In the literature, a bit rate of 4.7 Mbits/sec is generally used along with 133 minutes of high quality video to describe DVD Video performance from a single sided, single layer disc. Top

(VCD)Video CD
A Video CD uses a format that is rarely seen nowadays. It looks the same as a music CD or a CD-ROM, except that instead of music or software, it holds movies, using compressed MPEG-1 video files. VCD has a resolution of 352x288 (PAL) or 352x240 (NTSC), and has a quality which is roughly comparable to VHS. Top