A   S t r e a m i n g   M e d i a   P r i m e r :  

G L O S S A R Y

GLOSSARY

adaptive streaming: See MBR.

AVI:  Defi ned by Microsoft,  AVI  stands for Audio 

analog:  The principal feature of analog representa 

Video Interleave. AVI is the standard fi le format for dig 

tions is that they are continuous. For example, clocks 

ital video on the Microsoft  Windows  platform.  AVI 

with hands are analog the hands move continuously 

is not a streaming format; ASF (Advanced Streaming 

around the clock face.  As the minute hand goes around, 

Format) is the Windows Media streaming format.

it not only touches the numbers 1 through 12, but also 

bandwidth:  The data carrying capacity of a network. 

the infi nite number of points in between. Similarly, our 

Bandwidth is the maximum amount of data that can 

experience of the world, perceived in sight and sound, 

travel a communications path in a given time, usually 

is analog. We perceive infi nitely smooth gradations of 

measured in kilobits per second (Kbps). If you think 

light and shadow; infi nitely smooth modulations of 

of the communications path as a pipe, then bandwidth 

sound. Traditional (non digital) video is analog.

represents the width of the pipe, which determines how 

animated GIF:  GIF is a bitmap fi le format often used 

much data can fl ow through it at once. Connections 

on the Web. GIF (which may be correctly pronounced 

of 56 Kbps or lower (typical dial up connection rates) 

as either  giff   with a hard  g  or  jiff  ) stands for 

are considered low bandwidth, aka narrowband. High 

Graphic Interchange Format. Because it applies data 

bandwidth, aka broadband connections are higher than 

compression, GIF is often used for photographic imag 

56 Kbps (e.g., ISDN, DSL, cable modem, T 1).

es. An animated GIF combines several images into a 

bit: The smallest unit of data used by computer 

single GIF fi le. Applications that support the animated 

systems. A bit (short for binary digit) has a value of 

GIF standard (GIF89A) cycle through the images, 

either 0 (nil) or 1. Bits are the  building blocks  of 

creating the impression of motion. The animated GIF 

binary data.

format does not provide as much control and fl exibility 

bit depth: See bitmap.

as other animation formats but, because it is supported 

by nearly every Web browser, has become very popular.

bitmap: Also known as raster, bitmap data comprises 

a set of binary values specifying the color of individual 

architecture: The structure of the software, or the 

pixels that make up an image. Bitmap data is character 

system of software components, responsible for the 

ized by resolution  and  bit depth. Resolution relates to 

creation, storage, and playback of multimedia content. 

the detail in an image, and is expressed in dots per inch 

An architecture may include such things such as encod 

(dpi) or pixels per inch (ppi). The higher the resolution 

ers, compression/decompression support, fi le formats, 

(i.e., the more dots used to describe the image), the 

server software, and browser plug ins. Different multi 

more detail possible. Bit depth defi nes the number of 

media architectures offer different features and options, 

colors the image can display. A high contrast (no grey 

and store data in different fi le  formats.  QuickTime, 

tones) black and white image is 1 bit, meaning it can be 

RealVideo, and Windows Media are examples of stream 

off or on, black or white. As bit depth increases, more 

ing media architectures.

colors become available:

artifact: Visible degradations of an image resulting 

from any of a variety of processes. In digital video, 

  Bit depth               Maximum colors

artifacts usually result from color compression, and 

1                                    2

are most noticeable around sharply contrasting color 

boundaries such as black next to white.

2                                    4

ASF:  Defi ned by Microsoft,  ASF  stands for Advanced 

4                                    16

Streaming Format. ASF is the fi le format in the Windows 

8                                    256

Media architecture.

16                                 32,768

ASP:  An application service provider (ASP) is a third 

party entity that manages and distributes software 

24/32                           16.7 million                              

based services and solutions to customers across a wide 

area network from a central data center.

For image detail and quality, bit depth is as important 

as resolution, since the bit depth determines the colors 

aspect ratio: The ratio of an image's width to its 

available in the palette. When fewer colors are available, 

height. For example, a standard video display has an 

areas that may have shown a subtle shift of tones and 

aspect ratio of 4:3.

hues are rendered instead as single blocks of solid color, 

asynchronous: Not coordinated in time; contrasted 

eliminating image detail. Bitmap data is indispensable 

with synchronous. In a typical synchronous protocol, 

for continuous tone images, such as scanned or digital 

namic Media

each successive transmission of data requires a response 

photographs, and for anti aliased images. However, 

y

to the previous transmission before a new one can be 

bitmap data is consistently larger than vector data. Each 

initiated. An asynchronous protocol allows transmis 

pixel in a bitmap image has to be defi ned. A relatively 

sions to occur independently of one another. In com 

small 150 pixel x 150 pixel graphic requires 22,500 

puter communications using asynchronous protocols, 

discrete bits of information plus the palette, or color 

each piece of data usually has a start bit at the begin 

lookup table (CLUT), that is usually included. For more 

obe D

ning and a stop bit at the end, so that the valid 

information see the online Adobe Technical Guides at 

d

data can be distinguished from random noise. Most 

http://www.adobe.com/support/techguides/livemotion/

A

communications between computers and devices are 

lmobjects/page2.html

asynchronous; the public Internet is based on an asyn 

42

chronous system.