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Glossary of Terms
Aspect Ratio - The height to width ratio in PC and TV monitors. In video terms, the display frame can have different rectangular shapes, determined by its recording aspect ratio. Standard television is shown in a ratio of 4:3 (4 units of width to 3 units of height), whereas High Definition displays with a ratio of 16:9. DVD-Video also offers anamorphic and letterbox display formats as options. Not all TV sets offer a 'widescreen' option, and viewing a film using a different aspect ratio shows black bars at the top and the bottom of the screen.
AVI Audio-Video Interleaved - the format specified for Video for Windows (Microsoft), which, as implied, carries video and audio coding in an interleaved stream.
Bandwidth - Originally a range of frequencies, in current computer industry it describes the capacity or amount of traffic (data, voice, video, etc) per unit of time. In computerized communications it is expressed in Mbits/sec. Some of the new microcomputer buses and local buses have bandwidths of about 132 MBytes/sec.
Byte - A Byte is a section of computer data, which is basically the smallest unit of measure in data storage terms. A byte consists of 8 bits (a bit is a 1 or a 0, binary data), so, for example, 2 bytes actually can contain up to 16 bits. Many data storage devices sometimes store data incompletely in a byte, (for example, they store 14 bits in a 2 byte range), which after some time can lead to fragmentation, or empty gaps between the bytes. All data devices, such as floppies, hard drives, CDs and DVDs all record data in terms of bytes.
Capacity of CD-ROM - In general, the term capacity refers to the capacity of a standard 12cm CD, in megabytes of user data. Currently, there are CD-ROM media that can hold 74 or 80 minutes of data (80 min. is the maximum designed capacity). Originally, the maximum was only 74 minutes (of 640 MB of data), which is approximately the length of Beethoven's Ninth Symphony. The user data capacity of the CD-ROM is the number of user bytes per sector, times 75 sectors (user data) per second, times the total time recorded in the disc. Furthermore, the total, in Megabytes, will depend on the definition of Megabyte (2 ^20, or Million bytes). Therefore, for a 60 min. CD-ROM, we arrive to the figure of true 527 Megabytes. Obviously, this figure will be much higher for an 80-minute CD-ROM. Moreover, with multimedia CD-ROMs, capacities have the ability to record in "Mode 2", which allows more space for user data (2336 bytes/sector). It is therefore possible to produce a 74- minute disc, in Mode 2, with about 741 true Megabytes of user data in it--within the ISO 9660 specifications. Using millions to mean megabytes (or billions to mean Gigabytes), the figures will obviously be slightly larger--and this practice has become more common. Users must take these variables into account when discussing CD capacities.
Capacity of DVD - The DVD specifications emphasize the 12cm disc, which involves single and dual-layer, as well as single and double- sided discs, as shown in the following chart. The generic designations are: DVD-5, DVD-9, DVD-10 and DVD-18. DVD-R is implemented with a capacity of 3.95GB, and DVD-RAM with a capacity of 2.66GB--although now DVD-Rs are 4.7 GB and DVD-RAMs match that in Type II. Incidentally, we should also note that the DVD specifications include the much-less common 8cm format, with the same layer and side options of the 12cm disc--their corresponding capacities are shown below. The playing time of a DVD Video depends on the average video stream, which depends on the quality of video and audio output. An average video stream of 4.7 Mbits/sec leads to 133 minutes playing time per single layer--a figure often used to mean much more than that.
|12cm.||4.7 GB||8.5 GB|
|8cm.||1.4 GB||2.6 GB|
|12cm.||9.4 GB||17.0 GB|
|8cm||2.9 GB||5.3 GB|
New media coming out now has dual layer (8.4 GB of storage capacity)… however it should be noted that this is brand new and will not work on a majority of set-top DVD players.
CD - The Compact Disc was first implemented commercially for storing digital audio data (CD-Digital Audio). The physical specifications for the 12cm disc, since known as CD have become an international standard. The CD is made up of a polycarbonate substrate, a thin reflective metallic layer (the mirror-like material is aluminum), and a lacquer coating. The encoded data track is a continuous spiral track of about 1.6 to 2.2 microns wide, and the pits are about 0.6 microns wide.
CD-Recordable - CD-Recordable technology allows production of CD-ROMs on the desktop ('one-offs'). It requires a PC, a CD-R recorder or drive, appropriate software, and 'recordable' media. The 'one- off' is very different from replicated CDs. It is sold pre-grooved, in 74 or 80 minute capacities, and it involves a layered structure--with a sensitive chemical recording layer. Once recorded, the CD-R disc (one-off) is read in the same way as the replicated CDs.
CD-ROM - The Compact Disc-Read Only Memory is the standard 12cm CD formatted according to the ISO 9660. Although the physical characteristics and track structure of a CD-ROM are the same as that of CD-Audio, a CD-ROM is used to store computer data (text, graphics). The logical volume and file structure of CD-ROM, specified in the ISO 9660 allows it to be used in the computer arena. Therefore, a CD with computer data that is not structured according to the ISO 9660 is not a standard CD-R.
Compression - The large file size of audio, graphics and video files for CD-ROM applications reinforced the development of hardware and software compression-decompression procedures. Most compression algorithms are designed with specific types of files in mind (text, audio, video, graphics, etc).
CSS - Content Scrambling System, 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 or on an add-in board in the PC, 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).
DAT - Digital Audio Tape, generally high-quality 4mm magnetic tape in a cassette, with capacities up to over 1 Gigabyte, that has been used in the computer industry (where it is referred to as DDS) mainly as an archival and back-up medium. For CD-ROM, it is used as a transfer medium. For DVD, which deals in gigabytes, DAT has been replaced by Digital Linear Tape (DLT).
DLT (Digital Linear Tape) and SDLT (Super Digital Linear Tape) - DLT is the standard for replication and transfer of DVDs because they offer a higher storage capacity than do DDS (DAT tapes specifically made for computer data) tapes. DLT tapes can range in storage from 10 to 40 GB. The new SDLT format allows double that capacity, up to 80 GB with compression (see compression). DLT is the standard for use in making DVD stampers, however, many replicators can now make stampers from DVD-R media as well.
Digital Bin - In cassette production, a digital audio playback device replaying sound representing both sides of a cassette repeatedly at high speed.
Digitization - Digitization generally refers to the process of converting data and information (in paper, analog sound tracks, graphics, etc..) into binary coded files for use in computers. Text can be typed or OCR'd, graphics are scanned, analog video signals are digitized, sound is sampled and quantized, and so on.
DVD - stands for Digital Versatile Disc, since it can be used with Video, Audio or computer data. DVD is also used generically as the defined "Orange Book" standard for a disc that can be used in a DVD Player or DVD-ROM computer drive. A disc must be setup only in this way in order to receive a "DVD" logo stamp on it.
DVD-R - DVD - Recordable. DVD-R has a capacity of up to 4.7 GB per side, and uses dye polymer technology (same as CD-R). New to the market are 'dual-layer' DVD-Rs, which have a total data capacity of 8.4 GB. Although the new media will read in many conventional DVD-ROM computer drives, most set-top players will not recognize them.
DVD-Audio - An extension of the DVD specification, which applies to audio-only discs of much higher capacity. DVD-Audio discs can only be played in players that specifically support this format. It is useful for creating or archiving large volumes of audio work (such as the complete symphonies of Mozart), but users need to be aware that not all players will read and playback DVD-Audio unless the players specifically states it on the front of the unit.
Encoding - In the computer industry, programmers and users see and work with higher level languages, but the processors deal with machine languages and binary code. To use optical technology, it was necessary to develop an encoding scheme that would produce an effective optical code of pits and lands (pits are the data and the lands are the gaps between each pit)--one that can be decoded easily to produce the 8-bit code used by the PC. The resulting optical encoding scheme, uses a 14-bit byte (see Byte)--in which the 1s represent the transitions between lands and pits, and the 0s represent the run-lengths. In addition, there are various other sets of system and error detection and correction bits that are encoded so that the technology works as designed--but the user does not deal with these. The mastering machines do the encoding, and, when reading the disc, the controller card of the drive does all the decoding. For video compression, as in MPEG encoding or decoding, these terms refer to the creation of codes (frequency coefficients) that are used to represent the 'compressed' video stream, and to the decompression or 'decoding' that is performed to produce the video frame on the user's screen.
Frame Rate - Commonly, frame rates are used to imply video display speeds, and the higher the frame rate (video speed) the better the motion (up to 30 frames/sec). But, users must be aware that a video clip involves two frame rates: a compression frame rate and a display frame rate, and these can be different due to hardware, type of video, and other variables.
Full-motion Video - In general terms, it implies video display of continuous movement, at a frame rate that minimizes delays between frames (jerkiness of movement in the picture). More and more, however, it is used to mean full-screen video that plays at 29.97 frames/sec in NTSC format, or 25 frames/sec in PAL format.
Injection Molding - This is a common industrial process to produce plastic products of all shapes. The injection molding machines fitted with appropriate stampers, stamp or press the molten polycarbonate. Thus, the replicate is allowed to cool before it is then metallized and given a coat of protective lacquer.
Jewel Case - This is the clear plastic shipping and storage case for CD/DVDs. The disc sits on a transparent or opaque plastic tray with plastic 'fingers' in the center to secure the disc from moving excessively.
JPEG - A versatile and popular color graphics compression specification adopted by the Joint Photographic Experts Group. JPEG images are popular on the web because the compression that they use allows them to be made very small, so they are easy to transfer and take up small space on a web server, CD-ROM, etc. Many scanners for computers can now scan an image directly to a JPEG image (for emailing, storage, etc.)
MPEG - A codec adopted by ISO's Motion Pictures Expert Group for compression and playback of full-motion video and audio streams. There are many different versions of the MPEG codec, the most popular are the MPEG-1 format, commonly used to encode video to CDs, MPEG-2 which is used to encode DVD video, and MPEG-4 which is an updated version of MPEG-2 and widely used by broadcasters to compress and stream video.
Multimedia - This is the exciting and still growing arena of applications that use CD-ROM and DVD-ROM. Multimedia applications include text, sound, and motion video in what are mostly new categories of informational, educational, and entertainment products--and which have also helped define the new arena of 'infotainment.' Multimedia uses CD-ROM as its main file storage device, however DVD-ROM is gaining popularity also. Since video files can be very large, multimedia has led to the growth of specialized software, efficient hardware, and compression solutions.
NTSC - The National Television Standards Committee supports the NTSC signal and display technology used in the TV industries of North America, Japan, and a many other countries. It specifies 525 lines/screen, and 29.97 frames/sec.
PAL - Phase Alternating Line, a television standard that is used by European, Asian and some Latin American Countries. It specifies 625 lines/screen running at a frame rate of 25 frames/second.
Replication - In optical technology, replication refers to mass replication of optical discs (CD/DVD). See injection molding.
ROM - Read Only Memory. The term originally applied to read-only memory chips used in computers. With the growth of optical storage, the term read-only now includes compact disc products (CD-ROM, CD-I, CD-ROM XA, CD-Recordable, etc) as well as DVD disc products (DVD-R, DVD-RW, DVD+R, DVD+RW, and DVD-RAM)
SECAM - The television standard for France as well as some African and Russian stations. The color is actually recorded in the vertical interval, unlike PAL and NTSC which record in the horizontal 'blanking area' SECAM stands for Sequential Coleur avec Memoire and has a video specification of 625 lines/frame and 25 frames/second. All broadcast formats (for example, HDCAM, Betacam SP and Digital Betacam) do not support SECAM; instead a PAL tape must be made, with a standards conversion taking place at the time of airing.
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/sec is the top usable limit. But, MPEG-2 implements variable bit rate encoding (often called variable rate bitstream encoding), because it helps optimize quality in the program video stream while providing for maximum compression. Essentially, the sequences with high degree of motion are allowed higher data rates than the sequences with lower degrees of motion. It uses track buffers, intermittent reads, and even a complex '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 maximum of 9.8 Mbits/sec (higher rates up to the 11.08 Mbits/sec will not play in DVD-drives and players). An average 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 layer disc (capacity up to 4.7 gigabytes of data).
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