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A Short Glossary Of Terms For Video Compression And Production

4:1:1 sampling is used in 525/59.94 (“NTSC”) DV and DVCAM, and in both 525/59.94 and 625/50 (“PAL”) DVCPRO.  4:1:1 has 50% less chrominance bandwidth than 4:2:2. This reduced bandwidth increases noise and decreases chrominance dependent tasks (such as chromakeying).   The color data are sampled half as frequently as in 4:2:2, resulting in 180 color samples per scanline. The U and V samples are considered to be co-sited with every fourth luminance sample.

4:2:2 sampling is used in ITU-R BT601, D-1, D-5, Ampex DCT, Digital Betacam, Digital-S, and DVCPRO50 formats.  The color is sampled at half the rate of the luminance, with both color-difference samples co-sited (located at the same place) as the alternate luminance samples. Thus you have 360 color samples (in each of R-Y and B-Y) per scanline.

Anti-aliasing is why 640 x 480 looks good on TV and not on your PC.  Anti-aliasing smooths the jaggies from the edges of objects.

Aspect ratio is the ratio of video height to video width. The standard is 3:4, letter box is 16:9.

Chroma The color information in a video signal, consisting of hue and saturation.

Clipping is used to remove the unwanted portions of a frame from the edges of video.  This is one method of converting 4:3 to 16:9 and vice Versa

De-Interlacing takes two interlaced frames and creates one standard frame.

Interlacing produces one field of picture composed of alternate scanning lines, approximately every 1/60 of a second in NTSC. Two fields comprise one television frame resulting in the NTSC television frame rate of approximately 30 fps.

Inverse Telecline is the conversion of tape to film (30 fps to 24 fps) or the process of extracting the 24 original frames per second of a video that has been teleclined.

N.T.S.C. National Television Standards Committee created this first international television system for use in the U.S. and other countries. It produces pictures by creating 525 alternating lines across the TV screen for each frame of video.

After Effects: The most popular software for creating high-end 2D graphics effects in video. In structure After Effects permits separating image components into various layers. It also allows for extremely precise movement of these layers, precise synchronization between various elements, and rendering of the final output into a wide variety of digital formats.

Aspect Ratio: The relationship of width and height. When an image is displayed on different screens, the aspect ratio must be kept the same to avoid “stretching” in either the vertical or horizontal direction. The traditional aspect ratio for video is 4 horizontal units to 3 vertical units. Expressed in terms of pixels, a video signal would translate to an image 640 pixels wide by 480 units high. By contrast a 35mm slide has an aspect ratio of 3 horizontal units to 2 vertical units.

Assemble Edit: An analog edit process where one shot is linked to another like assembling the cars on a train. In assemble editing you can only put a shot after the last existing shot on your edit tape.

Analog Video: Analog is a continuously variable single, as opposed the discreet sampled information of a digital signal. In video this usually refers to video as stored on VHS or other more traditional tape formats. Most cameras also generate analog video. Video is usually converted from analog to digital format for editing or processing.

AVI: Audio Video Interleaved. File format for digital video and audio under Windows. File format is cross-platform compatible, allowing *.AVI video files to be played under other operating systems.

B-Roll: Footage shot to provide illustration of a concept, situation, or process. Also used to cover transitions and edits. Good B-Roll can enhance the message of a video by providing a visual interpretation of the verbal information.

Bandwidth: A term which usually refers to the size of the data stream supported in a digital enviroment. This relates directly to the size and resolution of the video information which can be supported. Bandwidth is usually expressed in terms of data per second. For example a hard drive may support a bandwidth of 10 MB/second, a CD-ROM could support a bandwidth of 300 KB/second, and a 56k Modem a bandwidth of 25KB/second.

Betacam-SP: A very high quality tape format develop by Sony Corporation where an analog video signal is stored in component format on a half inch tape. Betacam format is ideal for editing and digital conversion because there is very little loss in copying or transmission. Betacam is sometimes confused with Betamax, which was the original half inch video recording format.

Betamax: Sony’s original half-inch video format, used for home recording and tape distribution. Betamax tapes are about the size of a paperback book. This format rivaled VHS format for several years but by the late 1980’s was declining in popularity.

Blue Screen: Sometimes used as a alternate term to Chromakey. This refers to the blue background used behind foreground object in the Chomakey process.

Chromakey: Electronically matting or inserting an image from one camera into the picture produced by another Also called “keying.” The subject to be inserted is shot against a solid color background. Signals from the two sources are merged through a special effects generator.

CODEC: Literally, “Compression – Decompression”. An uncompressed video signal requires approximately 25 MB of information per second. Codecs allow the compression of this data into a smaller size for efficient playback and storage. There are many different codecs, each is usually optimal for a specific use, such as video editing, or web streaming. Some sample video codecs are M-JPEG, Cinepak, Indeo, MPEG-1, MPEG-2, and Sorenson.

Component Video: Video that has not been converted into a encoded video standard such as NTSC, SECAM, or PAL. This is a very high quality form of video and is excellent for analog-digital conversion. Component video can also be copies from one generation to the next with relatively high quality.

Composit Video: A video signal in which the luminance and chrominance elements have been combined, into an encoded signal such as in NTSC, PAL and SECAM. This is the most common form of how analog video is stored. Because these encoding standards were developed 30-40 years ago they do not offer a high quality alterative for video production. Nevertheless video is often distributed in these formats since most television sets require an encoded signal to display the video.

Control Track: A signal found on all video tape that is roughly analogous to sprocket holes on film. Control track can be used to count frames of video, and if SMPTE time code is not present may be the only way to identify places on a tape. These locations are expressed in time format. Since there is control track has no information it can be lost if the counter is reset.

Digital Video: A video signal expressed in a binary form. Digital video is stored in a file format similar to other computer based data. Some digital video is variable in size and playback speed depending on the specific application that it is used. CD-ROM, web streaming, and video used in editing and graphics are examples of digital video. Some examples of digital video formats that can play back on a television screen are D1, D2, D3, DVcam, miniDV, SDI, and DVpro.

DVD (Digital Video Disc or Digital Versatile Disk): A 12 cm optical disc format designed to function as a data storage medium. When fully implemented it has the potential of replacing other optical media such as the laserdisc, audio CD, and CD-ROM. It also has the potential of replacing VHS tape as a distribution format for movies.

Field: The video signal is divided into individual frames. Functionally speaking there are 30 video frames per second. Each of these frames is divided into two equal fields. An entire video frame has 525 horizontal lines of information. The duration of a video field is 1/60 of a second, and each frame has 262 lines of information.

Frame: A single, complete picture in video or film recording. A video frame consists of two interlaced fields of either 525 lines (NTSC) or 625 lines (PAL/SEACAM), running at 30 frames per second (NTSC) or 25 frames per second (PAL/SEACAM).

HDTV (High Definition Television): There are any number of specifications that could apply to this term. In 1941, our current 525 line system was referred to as HDTV. Today, this name is applied to several expanded resolution systems that are coming into place for our future entertainment and information delivery system(s). Several of the proposed HDTV systems claim to have a picture resolution equal to that of a projected 35 mm film print.

JPEG (Joint Photographics Experts Group): A digital storage format for images, either still or moving, which allows the data to be highly compressed for more efficient storage. The typical JPEG compression ratio is 1 to 10. Digital video uses a variation of this format called M-JPEG.

Kelvin: This is a system or scale used for measuring temperature. Absolute zero is 0° Kelvin or -273° C. The “color” of white light is expressed in terms of degrees Kelvin, the color of light emitted when an ideal object is heated to a particular temperature. Tungsten light is typically warmer in tone and has a Kelvin rating of 3000 to 3200 degrees. Daylight, the light emitted by most computer screens, and fluorescent lamps is much cooler and is rated around 5000 to 10000 degrees Kelvin.

LCD (Liquid Crystal Display): Created by sandwiching an electrically reactive substance between two electrodes, LCDs can be darkened or lightened by applying and removing current. Large numbers of LCDs grouped closely together can act as pixels in a flat-panel display.

Letterbox: The projected aspect ratio of feature films is often wider than our 525 or 625 line video formats. It is becoming common practice to transfer the composed aspect ratio of films to video by placing black boarders at the top and bottom of the film picture in the video. The film picture becomes a “letterbox” within the video

Lossless Compression: Ensures that the original data is exactly recoverable with no loss in image quality.

Lossy Compression: The original data is not completely recoverable. Although image quality may suffer, many experts believe that up to 95 percent of the data in a typical image may be discarded without a noticeable loss in apparent resolution.

Luminance: Brightness; one of the three image characteristics coded in composite television (represented by the letter Y). May be measured in lux or foot-candles.

MPEG (Motion Picture Experts Group): One of the most popular format for video compression, MPEG comes in a variety of forms. MPEG-1 is often used in CD-ROM playback. MPEG-2 is used extensively in DVD storage as well as satellite transmission.

NTSC (National Television Systems Committee) Format: A color television format developed in 1953 having 525 scan lines and a frame rate of 29.97 frames per second. NTSC is the standard for the U.S., Canada, Japan, Central America, ½ of the Caribbean & ½ of South America.

PAL (Phase Alternate Line): This is one of several composite video formats. The name describes something of how it works. PAL, in its many forms is used extensively in Western Europe. PAL is often known as “Peace At Last” because of the many compromises made in the evolution of the system and the fact that there are many forms of PAL.

RGB (Red, Green, & Blue): The basic components of the color television system. They are also the primary colors of light, not to be confused with Cyan, Magenta, and Yellow, the primary pigments.

S-Video: Type of video signal used in Hi8, S-VHS and some laserdisc formats. It transmits luminance and color portions separately, using multiple wires. S-Video avoids composite video encoding, such as NTSC, and the resulting loss of picture quality. Also known as Y-C Video.

Safe Action Area: This amounts to about 90% of the total picture area. It is symmetrically located inside of the picture boarder. Our home sets are over scanned. We don’t see the entire picture, the edges being lost beyond the boarder of the screen. Safe action area is designated as the area of the picture that is “safe” to put action that the viewer needs to see.

Safe Title Area: The area for safe title is inside the safe action area and amounts to about 80% of the total picture area. Titles and text are usually kept within the safe title area to make sure they can be seen in their entirety.

Scalability: A term often applied to web video, which describes the ability of the video stream to increase or decrease in direct proportion to the bandwidth available. A scalable video signal is far more resistant to frame dropping, stutter, and the other types of artifact that can disrupt web video.

Saturation: Practically speaking the amount of color information in a video (or computer image). On the typical television set this can be adjusted by the “Color” knob.

SECAM (“Sequential Couleur A Memoire” – sequential color with memory) Format: Video format used in France, Eastern Europe, F.S.U and other countries. 625 lines of resolution at 25 frames per second.

Telecine is the conversion of Film to Tape (24 fps to 30 fps)

Teleconference: A general term for a meeting not held in person. Usually refers to a multi-party telephone call, set up by the phone company or private source, which enables more than two callers to participate in a conversation. The growing use of video allows participants at remote locations to see, hear, and participate in proceedings, or share visual data (“video conference”).

TIFF: Tagged Image File Format. A bit map file format for describing and storing color and gray-scale images.

Time Code: A frame-by-frame address code time reference recorded on the spare track of a videotape or inserted in the vertical blanking interval. It is an eight-digit number encoding time in hours, minutes, seconds, and video frames (e.g.:02:04:48:26). Time code comes in couple of different formats which were defined by the Society of Motion Picture and Television Engineers (S.M.P.T.E.)

Vector Graphics: A digital file format for graphics where the information is based on a language which describes the form, colors, composition and other image attributes. PostScript is an example of such a language, and PostScript’s EPS format is the most common vector graphic format. Vector based graphics are much smaller than bitmapped, pixel based graphic files, and are ideal for Web use.

Waveform Monitor: A type of oscilloscope which is specifically used to measure the video signal. Waveform monitors are particularly useful for measuring lighting and detecting unwanted artifacts in the video signal.