Glossary

A

Advertising Application: A RealSystem Server option that inserts ads into SMIL-based presentations. SMIL files use <RealAdInsert/> tags to indicate ad placement.
artifact: A visual imperfection in an encoded video clip. Too many artifacts can make the video look blocky.

B

bandwidth: The upper limit on the amount of data, typically expressed as kilobits per second (Kbps), that can pass through a network connection.
banner ad: An ad that appears alongside a requested clip or presentation. A banner ad can also rotate, making new ad images appear at regular intervals.
binary tag: A SMIL tag that comprises opening and closing tags, such as <ref> and </ref>. Many unary tags can become binary tags when necessary to enclose other tags.
bit: The smallest unit of measure of data in a computer. A bit has a binary value, either 0 or 1.
bit rate: A measure of bandwidth, expressed as the number of bits transmitted per second. A 28.8 Kbps modem, for example, can transmit or receive around 29,000 bits per second.
blank time: A period during a presentation in which RealOne Player is not paused, but no activity occurs onscreen. You typically insert blank time with the SMIL begin attribute.
broadcast: To deliver a presentation, whether live or prerecorded, in which all viewers join the presentation in progress. Contrast to on-demand.
buffering: The receiving and storing of data before it is played back. A clip's initial buffering is called preroll. After this preroll, excessive buffering may stall the presentation.
byte: A common measurement of data. One byte consists of 8 bits.

C

cable modems: Devices that allow rapid transmission and reception of data over television cable. They are digital devices, unlike dial-up modems, which transmit analog data.
camel case: A capitalization convention in which words in a phrase are joined, and each word after the first begins with a capital letter. SMIL 2.0 attributes and values generally use camel case, as in soundLevel or whenNotActive.
CBR: Constant Bit Rate. A type of RealVideo encoding in which all parts of the video play back at the same bit rate. Contrast to VBR.
CHTTP: A version of HTTP supported by RealOne Player. Files designated with chttp:// are downloaded through HTTP and stored in RealOne Player's cache.
client: A software application that receives data from a server. A Web browser is a client of a Web server. RealOne Player is a client of RealSystem Server.
clip: A media file within a presentation. Clips typically have an internal timeline, as with RealAudio and RealVideo.
codec: Coder/decoder. Codecs convert data between uncompressed and compressed formats, reducing the bandwidth a clip consumes.

D

download: To send a file over a network with a nonstreaming protocol such as HTTP. Contrast to stream.
DSL: Digital Subscriber Line. A technology for transmitting digital data over a regular telephone line much faster than through dial-up modems.
duress stream: A low-bandwidth SureStream audio or video stream that RealSystem Server uses if a connection's available bandwidth drops greatly.

E

encoding: Converting a file into a compressed, streaming format. For example, you can encode WAV files as RealAudio clips.

F

Flash: A software application and an animation format created by Macromedia. RealOne Player can play Flash animations and stream them in parallel with other clips, such as RealAudio clips.
Flash Player file: A compressed Flash file format (file extension .swf) suitable for streaming. To stream Flash, you export the Flash Player file and tune it so that it plays well in RealOne Player.
fps: Frames Per Second. The number of video frames that displays each second in a streaming video clip.
frequency response: A measure of audio clip quality. The higher a clip's frequency response, the more frequencies it can faithfully reproduce.

H

HTTP: Hypertext Transport Protocol. The protocol used by Web servers to communicate with Web browsers. In contrast, RealSystem Server streams clips to RealOne Player with RTSP. See also CHTTP.

I

inline switching: Switching between alternative clips without using a SMIL <switch> tag.
interstitial ad: An advertisement that interrupts playback of a requested clip. It is like a commercial break on television.
ISDN: Integrated Services Digital Network. Technology that makes digital data connections at 64 or 112 Kbps possible over telephone lines.
ISP: Internet Service Provider. A company that provides access to the Internet. Many ISPs have RealSystem Server available to stream media clips.

K

kilobit (Kb): A common unit of data measurement equal to 1024 bits. A kilobit is usually referred to in the context of bit rate per unit of time, such as kilobits per second (Kbps).
kilobyte (KB): A common unit of data measurement equal to 1024 bytes or 8 kilobits.

L

LAN: Local Area Network. A computer network confined to a local area, such as a single building. LANs vary in speed, with bandwidth shared among all networked devices.
lossy: A compression scheme that lowers clip size by discarding nonessential data from the source file. Both RealAudio and RealVideo are lossy.

M

metafile: Another name for a Ram file.
mouseover: The action of moving a computer screen pointer over an interactive area. An animated button may change appearance on a mouseover, for example.

N

namespace: An XML declaration that identifies the features used in a SMIL presentation. For SMIL 2.0 and higher, the <smil> tag must declare a namespace.

O

on-demand: A type of streaming in which a clip plays from start to finish when a user clicks a link. Most clips are streamed this way. Contrast to broadcast.

P

PNA: A proprietary protocol RealSystem Server uses for backward compatibility with RealSystem 3 through 5. URLs using PNA start with pnm://.
port: A connection to a server, designated by a number such as 8080. RealSystem Server uses different ports for the RTSP, HTTP, and PNA protocols.
prefetch: To stream clip data to RealOne Player before the clip plays back. A clip's preroll can be prefetched minutes before the clip plays, for example, masking the preroll from the viewer.
preroll: Buffering that occurs just before a clip plays back. Preroll should be no more than 15 seconds.
presentation: A group of clips coordinated through SMIL and streamed from RealSystem Server to RealOne Player.

R

Ram file: A text file that uses the file extension .ram or .rpm. It launches RealOne Player and gives it the URL to a streaming clip or presentation.
RDT: The proprietary data package protocol RealSystem Server uses (along with RTSP) when communicating with RealOne Player. Contrast to RTP.
RealAudio: A RealSystem clip type for streaming audio over a network. RealAudio clips use the .rm extension.
RealOne Player: The successor to RealPlayer 8, RealOne Player combines streaming and digital download technologies. It supports the SMIL 2.0 and 1.0 standards.
RealPix: A RealSystem clip type (file extension .rp) for streaming still images over a network. RealPix uses a markup language for creating special effects such as fades and zooms.
RealPlayer G2: The RealNetworks client software that introduced plug-ins and the ability to update itself. It, along with the later RealPlayer 7 and RealPlayer 8, supports the SMIL 1.0 standard.
RealSystem Producer: The primary RealNetworks tool for encoding RealAudio and RealVideo clips.
RealSystem Server: RealNetworks server software used to stream multimedia presentations to RealOne Player.
RealSystem Server administrator: The person in charge of setting up and running RealSystem Server.
RealSlideshow: A RealNetworks tool for creating streaming slideshows based on the RealPix markup.
RealSystem: A general term for the entire RealNetworks system that streams media clips over a network. It consists of RealSystem Server, RealOne Player, and various production tools.
RealText: A RealSystem clip type (file extension .rt) for streaming text over a network. It uses a markup language for formatting text.
real-time: Delivered as it occurs. For example, a live event is streamed across a network in a real-time broadcast.
RealVideo: A RealSystem clip type for streaming video over a network. RealVideo clips use the extension .rm.
rebuffering: An undesirable state in which RealOne Player must pause a presentation to wait for streaming data to arrive. Rebuffering can result from network conditions, or a poorly produced presentation.
rotating banner ads: Banner advertisements that change at a specified interval, such as a new ad banner every 30 seconds.
RTP: Real-Time Protocol. The open, standards-based data package protocol RealSystem Server uses (along with RTSP) to communicate with RTP-based clients. Contrast to RDT.
RTSP: Real-Time Streaming Protocol. An open, standards-based control protocol that RealSystem Server uses to stream clips to RealOne Player or any RTP-based client. Contrast to HTTP.

S

server: 1. A software application, such as a Web server or RealSystem Server, that sends requested data over a network.; 2. A computer that runs server software.
Shockwave Flash: See Flash Player file.
SMIL: Synchronized Multimedia Integration Language. A markup language for specifying how and when each clip plays within a presentation. SMIL files use the extension .smil.
stream: 1. To send a media clip over a network so that it begins playing back as quickly as possible.; 2. A flow of a single type of data, measured in kilobits per second (Kbps). A RealVideo clip's soundtrack is one stream, for example.
SureStream: A RealNetworks technology that enables a RealAudio or RealVideo clip to stream at multiple bit rates.

U

unary tag: A SMIL tag that includes a closing slash, as in <ref/>. Many unary tags can become binary tags when necessary to enclose other tags.
URL: Uniform Resource Locator. A location description that enables a Web browser or RealOne Player to receive a clip stored on a Web server or RealSystem Server.

V

VBR: Variable Bit Rate. A type of RealVideo encoding that enables RealOne Player to play different parts of the video at different bit rates, even though the video is streamed at a constant rate. Contrast to CBR.

X

XML: Extensible Markup Language. The parent language for SMIL. XML allows one to develop flexible, standardized languages for any purpose.