Glossary J-Z
JPEG
Joint Photographic Experts Group. ISO/ITU-T. JPEG is a standard for the data compression of still pictures (intrafield). In particular its work has been involved with pictures coded to the ITU-R 601 standard. JPEG uses DCT and offers data compression of between two and 100 times and three levels of processing are defined: the baseline, extended and "lossless" encoding. See also: Motion-JPEG.
Kbps
Kilobits per second. Refers to transmission speed of 1,000 bits per second.
Keyframe
A set of parameters defining a point in a transition, such as a DVE effect. For example, a keyframe may define a picture size, position and rotation. Any digital effect must have a minimum of two keyframes, start and finish, although more complex moves will use more--maybe as many as 100. Increasingly, more parameters are becoming "keyframeable," meaning they can be programmed to transition between two, or more, states. Examples are color correction to made a steady change of color, and keyer settings, perhaps to made an object slowly appear or disappear.
Layered embedded encoding
The process of compressing data in layers such that successive layers provide more information and thus higher quality reconstruction of the original. That is, a single stream of data can supply a range of compression and thus, in the case of video, a scalable range of video resolution and picture quality. This is particularly useful for a muticast where a single stream is sent out and people are connecting over varying bandwidths. The low bandwidth connection can take just the lower layers while the high-bandwidth connection can take all of the layers for the highest quality.
Letterbox
Image of a widescreen picture on a standard 4:3 aspect ratio television screen, typically with black bars above and below. Used to maintain the original aspect ratio of the source material.
Live-streaming
Streaming media that is broadcast to many people at a set time.
See also: On-demand streaming.p> Lossless compression: Reducing the bandwidth required for transmission of a given data rate without loss of any data.
Lossy compression
Reducing the total data rate by discarding data that is not critical. Both the video and audio for DTV transmission will use lossy compression.
Luminance
The component of a video signal that includes information about its brightness.
See also: Chromininance: The color component of a video signal that includes information about hue and saturation.
Macroblock
In the typical 4:2:0 picture representation used by MPEG-2, a macroblock consists of four eight by eight blocks of luminance data (arranged in a 16 by 16 sample array) and two eight by eight blocks of color difference data which correspond to the area covered by the 16 by 16 section luminance component of the picture. The macroblock is the basic unit used for motion compensated prediction.
Mbps
Megabits per second.
Megabyte (Mbyte)
One million bytes (actually 1,048,576); one thousand kilobytes.
Metadata (side information)
Informational data about the data itself. Typically information about the audio and video data included in the signal´s data stream.
Motion compensation
The use of motion vectors to improve the efficiency of the prediction of pixel values. The prediction uses motion vectors to provide offsets into past and/or future reference frames containing previously decoded pixels that are used to form the prediction and the error difference signal.
Motion estimation
An image compression technique that achieves compression by describing only the motion differences between adjacent frames, thus eliminating the need to convey redundant static picture information from frame to frame. Used in the MPEG standards.
Motion-JPEG
Using JPEG compressed images as individual frames for motion. For example, 30 Motion-JPEG frames viewed in one second will approximate 30-frame per second video.
MOV
The file extension used by MooV format video files on Windows. These MOV files are generated with Apple Computer´s QuickTime and played on Windows systems via QuickTime for Windows.
MPEG
Compression standards for moving images conceived by the Motion Pictures Expert Group, an international group of industry experts set up to standardize compressed moving pictures and audio. MPEG-2 is the basis for ATSC digital television transmission.
Its work follows on from that of JPEG to add interfield compression, the extra compression potentially available through similarities between successive frames of moving pictures. Four MPEG standards were originally planned, but the accommodation of HDTV within MPEG-2 has meant that MPEG-3 is now redundant. MPEG-4 is intended for unrelated applications, however, can be used to display ATSC formats on a PC. The main interest for the television industry is in MPEG-1 and MPEG-2. A group of picture blocks, usually four, which are analyzed during MPEG coding to give an estimate of the movement between frames. This generates the motion vectors that are then used to place the macroblocks in decoded pictures.
MPEG-1
A group of picture blocks, usually four, which are analyzed during MPEG coding to give an estimate of the movement between frames. This generates the motion vectors that are then used to place the macroblocks in decoded pictures. This was designed to work at 1.2 Mbps, the data rate of CD-ROM, so that video could be played from CDs. However the quality is not sufficient for TV broadcast.
MPEG-2
This has been designed to cover a wide range of requirements from "VHS quality" all the way to HDTV through a series of algorithm "profiles" and image resolution "levels." With data rates of between 1.2 and 15 Mbps, there is intense interest in the use of MPEG-2 for the digital transmission of television--including HDTV--applications for which the system was conceived. Coding the video is very complex, especially as it is required to keep the decoding at the reception end as simple and inexpensive as possible. MPEG-2 is the compression used by the ATSC and DVB standards.
MPEG can offer better quality pictures at high compression ratios than pure JPEG compression, but with the complexity of decoding and especially coding and the 12-long group of pictures (GoP), it is not an ideal compression system for editing. If any P or B frames are used then even a cut will require the re-use of complex, and not perfect, MPEG coding. However, MPEG Splicers are beginning to appear to alleviate this difficulty.
Of the six profiles and four levels creating a grid of 24 possible combinations, 12 have already been implemented. The variations these define are so wide that it would not be practical to build a universal coder or decoder. Interest is now focused on the Main profile, Main level, sometimes written as MP@ML, which covers broadcast television formats up to 720 pixels x 576 lines at 30 frames per second. These figures are quoted as maximums so 720 x 486 at 30 frames are included, as are 720 x 576 at 25 frames. As the coding is intended for transmission the economy of 4:2:0 sampling is used.
A recent addition to MPEG-2 is the studio profile. Designed for studio work its sampling is 4:2:2. The studio profile is written as 422P@ML. To improve the picture quality, higher bit rates are used. The first applications for this appear to be in electronic news gathering (ENG), and with some video servers.
See also: B frames, Compression, GoP, I frames, JPEG, P frames.
MPEG-4
The third standard developed by MPEG. Started in July 1993 MPEG-4 has benefited from the huge R&D investments made by participating companies and provides a harmonised range of responses to the diverse needs of the digital audio-visual industry, including compatibility with other major standards such as H.263 and VRML.
MPEG 4:2:2
Also referred to as Studio MPEG, Professional MPEG and 442P@ML. Sony´s Betacam SX is based on MPEG 4:2:2. See: MPEG-2.
MPEG-7
A standardized description of various types of multimedia information. This description will be associated with the content itself, to allow fast and efficient searching for material that is of interest to the user. MPEG-7 is formally called "Multimedia Content Description Interface." The standard does not comprise the (automatic) extraction of descriptions/features. Nor does it specify the search engine (or any other program) that can make use of the description. It is not a new compression standard, but an attempt to manage motion imaging and multimedia technology.
MPEG-21
The Motion Picture Experts Group´s attempt to get a handle on the overall topic of content delivery. By defining a Multimedia Framework from the viewpoint of the consumer, they hope to understand how various components relate to each other and where gaps in the infrastructure might benefit from new standards. A technical report on the MPEG-21 framework is scheduled for mid-2000.
MPEG IMX
Sony´s trademark for a family of devices, such as DVTRs, that are I frame-only 50 Mbps MPEG-2 streams using Betacam style cassettes. Plays Digital Betacam, Betacam SX, Betacam SP, Betacam, and, MPEG IMX, outputting 50 Mbps MPEG I-frame on SDTI-CP regardless of the tape being played. It can also handle other (lower) input and output data rates, but the recordings are 50 Mbps I-frame in any case.
Multicast
1. Data flow from single source to mutiple destinations; a multicast may be distinguished from a broadcast in that number of destinations may be limited. 2. Aterm often used incorrectly to describe digital television program multiplexing.
Noise
Unwanted and unmodulated energy that is always present to some extent within any signal.
Nonlinear
A term used for editing and the storage of audio, video and data. Information (footage) is available anywhere on the media (computer disk or laser disc) almost immediately without having to locate the desired information in a time linear format.
Nonlinear editing
Nonlinear distinguishes editing operation from the "linear" methods used with tape. Nonlinear refers to not having to edit material in the sequence of the final program and does not involve copying to make edits. It allows any part of the edit to be accessed and modified without having to re-edit or re-copy the material that is already edited and follows that point. Nonlinear editing is also non-destructive--the video is not changed but the list of how that video is played back is modified during editing.
NTSC
National television system committee. The organization that developed the analog television standard currently in use in the U.S., Canada, and Japan. Now generally used to refer to that standard. The NTSC standard combines blue, red, and green signals modulated as an AM signal with an FM signal for audio. See also: PAL and SECAM. H.320 A recommendation of the ITU-T based on Discrete Cosine Transform, CCM and motion compensation techniques. It can be a video system´s sole compression method or supplementary algorithm, used instead of a proprietary algorithm when two dissimilar codecs have need to interoperate. H.320 includes a number of individual recommendations for coding, framing, signaling and establishing connections. It also includes three audio algorithms, G.721, G.722 and G.728.
On-demand streaming
Streaming media content that is transmitted to the client upon request.
PAL
Phase alternate line. The television broadcast standard throughout Europe (except in France and Eastern Europe, where SECAM is the standard). This standard broadcasts 625 lines of resolution, nearly 20 percent more than the U.S. standard, NTSC, of 525.
Pan and Scan
The technique used to crop a widescreen picture to conventional 4:3 television ratio, while panning the original image to follow the on-screen action.
Pillarbox
Describes a frame that the image fails to fill horizontally (a 4:3 image on a 16:9 screen), in the same way that a letterbox describes a frame that the image fails to fill vertically (a 16:9 image on a 4:3 screen) See also: Letterbox and side panels.
Pixel
A shortened version of "Picture cell" or "Picture element." The name given to one sample of picture information. Pixel can refer to an individual sample of R, G, B luminance or chrominance, or sometimes to a collection of such samples if they are co-sited and together produce one picture element.
Point-to-multipoint
An arrangement, either permanent or temporary, in which the same data flows or is transferred from a single origin to multiple destinations; the arrival of the data at all the destinations is expected to occur at the same time or nominally the same time.
Progressive
Short for progressive scanning. A system of video scanning whereby lines of a picture are transmitted consecutively, such as in the computer world.
QCIF
See CIF.
QuickTime
Apple Computer´s system-level software architecture supporting time-based media, giving a seamless integration of video, sound, and animation. For Macintosh and Windows computers.
Real-Time
The processing of information that returns a result so rapidly that the interaction appears to be instantaneous. Telephone calls and videoconferencing are examples of real-time applications. These kinds of real-time information not only need to be processed almost instantaneously, but it needs to arrive in the exact order it´s sent. A delay between parts of a word, or the transmission of video frames out of sequence, makes the communication unintelligible. The telephone network is designed for real-time communication.
RealVideo
Popular software for streaming audio and video over the Internet. made by RealNetworks of Seattle, Washington.
Resolution
1. Detail. In digital video and audio, the number of bits (four, eight, 10, 12, etc.) determines the resolution of the digital signal. Four bits yields a resolution of one in 16. Eight bits yields a resolution of one in 256. Ten bits yields a resolution of one in 1,024. Eight bits is the minimum acceptable for broadcast television. 2. A measure of the finest detail that can be seen, or resolved, in a reproduced image. While influenced by the number of pixels in an image (for high definition approximately 2,000 x 1,000, broadcast NTSC TV 720 x 487, broadcast PAL TV 720 x 576), note that the pixel numbers do not define ultimate resolution but merely the resolution of that part of the equipment. The quality of lenses, display tubes, film process and film scanners, etc., used to produce the image on the screen must all be taken into account. This is why a live broadcast of the Super Bowl looks better than a broadcast recorded and played off of VHS, while all are NTSC or PAL.
Resolution independent
Term used to describe the notion of equipment that can operate at more than one resolution. Dedicated TV equipment is designed to operate at a single resolution although some modern equipment, especially that using the ITU-R 601 standard, can switch between the specific formats and aspect ratios of 525/60 and 625/50.
By their nature, computers can handle files of any size, so when applied to imaging, they are termed resolution independent. As the images get bigger so the amount of processing, storage and data transfer demanded increases--in proportion to the resulting file size. So, for a given platform, the speed of operation slows. Other considerations when changing image resolution may be reformatting disks, checking if the RAM is sufficient to handle the required size of file, allowing extra time for RAM/disk caching and how to show the picture on an appropriate display.
RGB
The abbreviation for the red, green and blue signals, the primary colors of light (and television). Cameras and telecines have red, blue and green receptors, the TV screen has red, green and blue phosphors illuminated by red, green and blue guns. Much of the picture monitoring in a production center is in RGB. RGB is digitized with 4:4:4 sampling which occupies 50 percent more data than 4:2:2.
Ringing
An oscillatory transient on a signal occurring as a result of bandwidth restrictions and/or phase distortions. A type of ringing causes ghosting in the video picture.
SDI: See Serial digital interface (SDI)
The standard based on a 270 Mbps transfer rate. This is a 10-bit, scrambled, polarity independent interface, with common scrambling for both component ITU-R 601 and composite digital video and four channels of (embedded) digital audio. Most new broadcast digital equipment includes SDI which greatly simplifies its installation and signal distribution. It uses the standard 75 ohm BNC connector and coax cable as is commonly used for analog video, and can transmit the signal over 600 feet (200 meters) depending on cable type.
SECAM
Sequential couleur avec mmoire. The television broadcast standard in France, the Middle East, and most of Eastern Europe, SECAM provides for sequential color transmission and storage in the receiver. The signals used to transmit the color are not transmitted simultaneously but sequentially line for line. SECAM processes 625 lines, a maximum of 833 pixels per line and 50 Hz picture frequency. SECAM is used as a transmission standard and not a production standard (PAL is typically used).
Serial digital data interface (SDDI)
A way of compressing digital video for use on SDI-based equipment proposed by Sony. Now incorporated into Serial digital transport interface. See: Serial digital transport interface.
Serial digital interface (SDI)
The standard based on a 270 Mbps transfer rate. This is a 10-bit, scrambled, polarity independent interface, with common scrambling for both component ITU-R 601 and composite digital video and four channels of (embedded) digital audio. Most new broadcast digital equipment includes SDI which greatly simplifies its installation and signal distribution. It uses the standard 75 ohm BNC connector and coax cable as is commonly used for analog video, and can transmit the signal over 600 feet (200 meters) depending on cable type.
Server (video)
A storage system that provides audio and video storage for a network of clients. While there are some analog systems based on optical disks, most used in professional and broadcast applications are based on digital disk storage.
Aside from those used for video on demand (VOD), video servers are applied in three areas of television operation: transmission, post production and news. Compared to general purpose file servers, video severs must handle far more data, files are larger and must be continuously delivered.
There is no general specification for video servers and so the performance between models varies greatly according to storage capacity, number of channels, compression ratio and degree of access to store material--the latter having a profound influence.
Store sizes are very large, typically up to 500 Gigabytes or more. Operation depends entirely on connected devices, edit suites, automation systems, secondary servers, etc., so the effectiveness of the necessary remote control and video networking is vital to success.
Set-top box (STB)
These receivers (named because they typically sit on top of a television set) convert and display broadcasts from one frequency or type--analog cable, digital cable, or digital television) to a standard frequency (typically channel 3 or 4) for display on a standard analog television set.
Side converting
The process which changes the number of pixels and/or frame rate and/or scanning format used to represent an image by interpolating existing pixels to create new ones at closer spacing or by removing pixels. Side converting is done from standard resolution to standard resolution and high definition to high definition. See also: Down converting, Up converting.
Side panels
Image of a standard 4:3 picture on a widescreen 16:9 aspect ratio television screen, typically with black bars on the side. Used to maintain the original aspect ratio of the source material. See also: Letterbox, Pillarbox.
SMPTE
1. Society of Motion Picture and Television Engineers, a professional organization that sets standards for American television. 2. An informal name for a color difference video format that uses a variation of the Y, R-Y, and B-Y signal set.
Stream
1. To transmit multimedia files that begin playing upon arrival of the first packets, without needing to wait for all the data to arrive. 2. To send data in such a way as to simulate real-time delivery of multimedia.
Streaming media
Multimedia content--such as video, audio, text, or animation--that is displayed by a client as it is received from the Internet, broadcast network, or local storage.
Sub-pixel
A spatial resolution smaller than that of pixels. Although digital images are composed of pixels it can be very useful to resolve image detail to smaller than pixel size, i.e., sub-pixel. For example, the data for generating a smooth curve on television needs to be created to a finer accuracy than the pixel grid itself, otherwise the curve will look jagged. Again, when tracking an object in a scene or executing a DVE move, the size and position of the manipulated picture must be calculated, and the picture resolved, to a far finer accuracy than the pixels, otherwise the move will appear jerky. See also: Pixel.
Sweetening
Electronically improving the quality of an audio or video signal, such as by adding sound effects, laugh tracks, and captions.
Table 3 Compression Format Constraints: See: ATSC.
TCP/IP
Transmission control protocol/internet protocol. An Internet protocol suite developed by the U.S. Department of Defense in the 1970s. TCP governs the exchange of sequential data. IP routes outgoing and recognizes incoming messages.
Temporal aliasing
A defect in a video picture that occurs when the image being sampled moves too fast for the sampling rate. A common example occurs when the rapidly rotating spokes of a wagon´s wheels appear to rotate backwards because of video scanning that moves more slowly than the spokes.
Temporal resolution
The ability of the display to reproduce adequate detail to allow the visual system to distinguish the separate parts or components of an object that is moving through the display.
Time code
1. Vertical interval time code (VITC). This is SMPTE time code that is recorded as video signals in the vertical interval of the active picture. It has the advantage of being readable by a VTR in still or jog. Multiple lines of VITC can be added to the signal allowing the encoding of more information than can be stored in normal LTC. 2. Linear time code (LTC). Time code recorded on a linear analog track (typically an audio channel) on a videotape. Also called longitudinal time code. Time code can be drop frame (59.94 Hz) that matches actual elapsed time by dropping occasional frames or non-drop frame (60 Hz) that runs continuously although it does not exactly match actual elapsed time.
Transcode
The process of converting a file or program from one format or resolution to another.
Up converting (up-rezing)
The process which increases the number of pixels and/or frame rate and/or scanning format used to represent an image by interpolating existing pixels to create new ones at closer spacing. Despite its name the process does not increase the resolution of the image. Up converting is done from standard definition to high definition.
Variable bit rate reduction: See: Compression.
Video for Windows
Microsoft´s system-level Windows software architecture that is similar to Apple Computer´s QuickTime.
Video-on-demand (VOD)
When video can be requested at any time and is available at the discretion of the end-user, it is then video-on-demand.
Wavelet-based compression
An asymmetrical image compression technique that is scalable and can provide high quality. The drawback is that it becomes more computationally expensive as the picture resolution and frame rates go up. The encode and decode are asymmetrical in that one side is a lot more expensive computationally than the other. The ImMix Cube and TurboCube used wavelet-based compression.
Widescreen
Term given to picture displays that have a wider aspect ratio than normal. For example, TV´s normal aspect ratio is 4:3 and widescreen is 16:9. Although this is the aspect ratio used by HDTV, widescreen is also used with normal definition systems.
Windows Media Player
Delivers the most popular streaming and local audio and video formats, including ASF, WAV, AVI, MPEG, Quick-Time, and more. Windows Media Player can play anything from low-bandwidth audio to full-screen video.
YUV
A color model used chiefly for video signals in which colors are specified according to their luminance--the Y component--and their hue saturation--the U and V components.
