4:2:0 Color—moderately compressed video color subsampling similar to 4:1:1. Standard color for MPEG.

4:2:2 Color—mildly compressed video color subsampling in which the luminance channel is not subsampled, but the chrominance channel has half the resolution. Commonly used in professional video formats, such as BetaCamSP.

Analog-to-Digital Converter (A/D)—chip that converts analog video signals to digital signals. A-to-D converters are used by video capture cards to convert video into a format that the computer can manipulate and store.

ASF—Active Streaming Format—standard file format of Windows Media files.

Codec—compressor/decompressor. A software component that translates video or audio between its uncompressed form and the compressed form in which it is stored. Sorenson Video and Cinepak are common QuickTime video codecs. Also called a "compressor."

Data Rate—amount of information per second used to represent a movie. A 2X speed CD-ROM movie is about 200 KBps. The data rate of uncompressed NTSC video is about 27 Megabytes per second.

Deinterlace—to remove the interlacing artifacts caused by the two-fields-per-frame nature of video.

Delta Frames—frames that contain only changes from previous frame. Delta frames are created by codecs that use temporal compression. Also called "difference frames."

Encode—in multimedia, this term means compressing a file.

FireWire—Apple's trademarked name for the IEEE 1394 standard, which is a very fast external bus, often used to connect DV cameras to computers. Some other companies use different names to describe their 1394 products, including "I-Link".

Flattening—final pass applied to a QuickTime movie, ensures movie data is laid out in a completely linear fashion, and all external references are removed.

FPS—frames per second—measure of the frame rate of video or film. NTSC video is 29.97 fps, PAL video is 25 fps, and film is 24 fps.

Frame Rate—number of frames per second of a movie.

Http Streaming—see "Progressive Download."

Indeo—several codecs developed by Intel that allow temporal and spatial compression as well as data rate limiting.

Inline—within the browser page, as opposed to needing to be viewed with an external application. Example: you normally view Flash movies "inline" on a page versus in a "viewer."

Keyframe—spatially compressed frame that contains the complete video image and is the basis for the following delta frames. Also called an "Intraframe."

Live Video—video that is captured, compressed, and distributed in real time. This is the opposite of "On-Demand" video. Live video systems must use fairly "symmetric" codecs to compress the video in real time.

MPEG-1—format that produces high- quality video and audio streams at approximately 2X CD-ROM data rates. Standard MPEG-1 is full frame rate (24—30 fps, depending on the source) with a quarter size image (352x240).

MPEG-2—format that produces high data rate, full broadcast quality files. MPEG-2 playback requires an extremely fast computer and video card, or a hardware accelerator card. MPEG-2 is the format for DVD-Video and many home satellite dish systems. Standard MPEG-2 is full frame rate (24—30 fps) and full screen resolution (720x480).

MPEG Layer-2 audio—generally used for high bandwidth MPEG audio at near CD quality. Used for audio with both MPEG-1 and MPEG-2.

MPEG Layer-3 Audio (MP3)—MPEG audio format. Generally used in audio-only files (.mp3 files). A lower-bandwidth format than MPEG Layer-2 audio, but still not ideal for modem streaming.

On-Demand—video that is not broadcast "live" as it is filmed, but is compressed and made available on a server for people to watch when they wish. A Webcast would be "live," while an online movie trailer would be "on demand." Most audio and video on the Web is "on demand."

Progressive Download—term referring to online media that users may watch as it downloads. Also called "HTTP Streaming" because standard HTTP Web servers can deliver progressive download files, and no special protocols are needed.

QuickTime—Apple Computer's cross-platform multimedia architecture.

RAM File—RealVideo reference file that is placed on the HTTP server and gives the RealPlayer the location of the Real movie file on the RealServer.

RealVideo—RealNetworks' streaming media architecture.

RealSystem G2—is the second generation of RealVideo. Also called simply "RealG2." This has now been replaced by Real version 8.

RTSP—RealTime Streaming Protocol—standard used to transmit true streaming media to one or more viewers simultaneously. RTSP provides for viewers randomly accessing the stream.

Sample Rate—number of samples per second used for audio. Higher sample rates yield higher quality audio that is larger than that of lower sample rates. Common sample rates include 11.025 kHz, 22.050 kHz, and 44.100 kHz (CD quality).

Sorenson Video Codec—high-quality, low-bandwidth QuickTime video codec.

Symmetric Codec—codec that encodes and decodes video in roughly the same amount of time. Live streaming systems use fairly symmetric codecs in order to encode video in realtime as it is captured.

True Streaming—refers to technologies that match the bandwidth of the media signal to the viewer’s connection, so that it’s seen in real time. "True" is added to differentiate this type of streaming from "HTTP Streaming" (see "Progressive Download"). Specialized media servers and streaming protocols such as RTSP are required to enable "true streaming."