Glossary
:: Video Glossary
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100Base-T Ethernet
A version of Ethernet that supports a transmission rate of 100 Mbps or megabits per second; it is often called Fast Ethernet because it is ten times faster than Ethernet.
ACC or Active Content Compression
A proprietary video compression algorithm designed for the video security environment that incorporates intraframe, interframe, and video noise immunity compression techniques (see ACC White Paper). Less expensive than MPEG-4, ACC lets you store and send more high quality images at faster update rates over phone lines and networks than any other compression technique.
Analog video signal
A video signal that takes the form of continuous waves and is displayed via a series of scans.
Bandwidth
The capacity for transferring data over a network as measured in bits per second (bps) or some multiple thereof such as kilobits per second (Kbps), mega, or one million bits per second (Mbps), gigabits per second (Gbps) and terabits per second (Tbps). How much information you can send across a network and how fast you can send it is determined by the available bandwidth. A 56K modem, for example, provides a bandwidth of 53.3 Kbps.
CIF or Common Intermediate Format
A commonly used television standard for measuring resolution. One CIF equals 352 x 240 pixels for NTSC and 352 x 288 pixels for PAL. Full resolution is considered 4CIF, which is 704 x 480 pixels (NTSC) and 704 x 576 pixels (PAL). Within the digital video industry, however, a CIF represents an approximation. The actual number of pixels in a CIF may vary slightly as long as they provide the same level of overall picture quality. With Intellex, for instance, 1CIF equals 320 x 240 pixels, 2CIF equals 640 x 240 pixels, and 4CIF equals 640 x 480 pixels.
Computer network
Two or more computers that are connected together to share resources such as hardware, data, and software. Most common are the local area network (LAN) and the wide area network (WAN). A LAN can range from a few computers in a small office to several thousand computers spread throughout dozens of buildings on a school campus or in an industrial park. Expand this latter scenario to encompass multiple geographic locations, possibly on different continents, and you have a WAN.
DHCP
An acronym that stands for Dynamic Host Configuration Protocol, which simplifies the transfer of data by assigning dynamic IP addresses—temporary addresses that are created anew for each transmission—to devices on the network. DHCP keeps track of both dynamic and static IP addresses, saving the network administrator the trouble of manually assigning them each time a new device is added to the network.
Digital signal
A video signal that is comprised from bits of binary data, otherwise known as 1s and 0s. A video signal travels from the point of its inception to the place where it is stored and then on to the place where it is displayed, either as analog or digital. It may be converted from one to the other, once or several times, while en route. Both digital and analog video signals are displayed with light and color intensity on fixed dots called pixels.
Gigabit Ethernet
A version of Ethernet that supports a transmission rate of 1 Gbps or one gigabit per second (the equivalent of 1000 Mbps or megabits per second).
Images per second (ips)
The speed at which images are transmitted. Motion in video, just as with film or cartoons, is conveyed by presenting slightly different images in rapid succession. Images are actually photographs of the same scene shot at split-second intervals, the difference between each revealing any action or change that has transpired since the one preceding it. The number of images per second, or speed at which the individual frames are transmitted, determines how closely the video approximates what you would see if directly viewing the event with your own eyes. The more images per second, the closer to what the human eye perceives.
IP
An acronym that stands for Internet Protocol. This network layer of the TCP/IP protocol used in transmission of data over a computer network such as a LAN, WAN, or the Internet. IP provides features necessary for the delivery of data including: device addressing, type of service specification, fragmentation and reassembly of data, and security.
IP address
A series of numbers that functions similarly to a street address, identifying the location of both sender and recipient for information dispatched over a computer network.
M-JPEG
A digital video compression format developed from JPEG (JPEG stands for Joint Photographic Experts Group and is a compression standard for still images). When JPEG is extended to a sequence of pictures in a video stream, it becomes M-JPEG or Motion-JPEG. Unlike other compression schemes, each frame is an image unto itself. M-JPEG is an intraframe technique that works well with single stream or multiplexed stream data, scales reasonably well, and can be implemented as either constant bit-rate or constant information codecs.
MPEG-4
A digital video compression standard for motion pictures developed along the lines of JPEG. MPEG-4 (MPEG stands for the Motion Picture Experts Group) was originally intended to replace video conferencing standards (H.320) but its usage has expanded to become, as some say, “everything to all people”. Yet it is much more computation and resource intensive than ACC. Other drawbacks include severe latency, significant hardware acceleration requirements, and an inability to scale well to multiple sources or multiplexed data streams.
Resolution
The number of pixels in an image. The more pixels, the higher the resolution. The higher the resolution, the better the picture. (A pixel, by the way, is a colored dot.) —See also CIF.
Switch
A device that splits a network into subsections, allowing users within each subsection to transfer data to one another without entering—and congesting—the rest of the network. A switched network is a network that uses a switch to maintain these subsections.
TCP/IP
An acronym that stands for Transmission Control Protocol/Internet Protocol, a set of protocols that has become the standard for communication between networks, including the Internet. To make transmission more efficient, information is broken down into individual units or packets of data. The Transmission Control Protocol portion of TCP/IP handles the tracking of those packets. —See also IP.
Video encoder
A device that converts an analog video signal to a digital video signal using one of a variety of compression schema.
Wavelet
A popular alternative to JPEG that is attributed with compressing an image more naturally than methods (like JPEG) that use cosine waves; the net effect is an image that gets softer and muddier vs. harsher and blockier. Computationally more expensive than JPEG, it is intraframe-only and performs less effectively than compression methods that use interframe technique (see ACC White Paper). Real time encoding performance, as with MPEG-4, requires hardware acceleration. No standards for wavelet compliance currently exist although the JPEG 2000 standard, which has yet to be widely adopted, includes a wavelet implementation section.