A
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Adaptive Stream Management (ASM)
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Rules that describe a streamed datatype to RealSystem, helping it make intelligent decisions about how to deliver that datatype's packets efficiently and robustly.
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asynchronous
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The ability to send or receive calls independently and in any order.
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Audio Services
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Device-independent, cross-platform features used by audio rendering plug-ins. The plug-in can use Audio Services without concern for the specifics of the audio hardware.
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authentication
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The process by which a plug-in performs password authorization by comparing username/password values sent in by a user against those stored in RealServer's encrypted password file.
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authentication manager
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The object that gathers a username and password from the user. This is typically the RealSystem top-level client.
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authentication request object
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The object with access to the username/password values to be authenticated. It provides these values to the authenticator object on request.
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authentication response object
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The object that receives notice that the authentication succeeded or failed. When the validation succeeds, the response object carries out the action, such as file access, that was originally requested.
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authenticator object
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An object instantiated by RealServer that performs authentication by comparing a username/password combination against RealServer's encrypted password file.
B
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Backchannel
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A communications channel from a client to RealServer. To stream data between server and client, RealSystem components use
IRMAPacket
objects. A file format plug-in, for example, prepares packets that RealServer streams to the client. As well, the file format's corresponding rendering plug-in can use the back channel to send packets of information back to the file format plug-in.
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bandwidth
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The amount of data that can be sent over a client's connection.
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Basic authorization
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A form of password authorization that uses unencrypted usernames and passwords.
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bit rate
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The rate at which a presentation is streamed, usually expressed in Kilobits per second (Kbps).
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broadcasting
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Streaming the same data source, whether live or prerecorded, to multiple clients. A broadcast application passes buffers of encoded data from a live source to the Remote Broadcast Library, which then connects to a RealSystem broadcast plug-in and delivers the stream to RealServer.
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buffering
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Receiving and storing data before playing it back. The initial buffering time is called preroll. After preroll, excessive buffering may stall the presentation.
C
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client
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An application, such as RealPlayer, that receives RealSystem presentations from RealServer.
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client core
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The part of a RealSystem client that handles data transport with RealServer and provides RealSystem features such as Audio Services.
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clip
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A media file within a presentation. Clips typically have an internal timeline, as with RealAudio and RealVideo.
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codec
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Coder/decoder. An algorithm for compressing files for use with RealServer. A variety of codecs exist for different streaming bit-rates and content types. For example, a 32-Kbps music codec is for high-quality music streaming, while a 6.5 Kbps voice codec works for a simple voice file.
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COM
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Component Object Model, a technology used by RealSystem for describing interfaces and exporting objects that implement those interfaces.
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Common Class Factory
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The
IRMACommonClassFactory
interface used by a component to create objects passed to other RealSystem components.
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container datatype
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A datatype, such as RealMedia File Format (RMFF) or ASF, that can contain other data types. Each container data type is identified by a unique MIME type.
D
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datatype
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A single datatype, such as RealAudio, RealFlash, or MIDI, that can be rendered by a client. Each data type is identified by a unique MIME type.
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DIGEST authorization
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A form of password authorization that uses encrypted usernames and passwords. Communication between RealServer and RealPlayer uses
DIGEST
authorization.
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dry stream
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A stream containing too little data for the RealPlayer to write to an audio device.
E
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encoder
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An application that converts various types of media files into RealSystem clips ready to be streamed by a RealServer. RealProducer is a standard RealSystem encoder used to create RealVideo and RealAudio files or live streams.
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expression
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An optional part of a rule that defines a condition the client evaluates. The client subscribes to the rule if the condition fits its current network connection.
H
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header
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A chunk of data, delivered from a source to a rendering plug-in when first connecting to a stream, usually used to initialize the stream.
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HTTP playback
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A reasonable method for sending short clips from a Web server using the HTTP protocol. HTTP streaming does not support all the datatypes of and is not as robust as RTSP streaming, however.
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hypernavigation
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Occurs when a rendering plug-in directs the client to display a URL at a specified time in a stream. When the plug-in issues a hypernavigation request, the default Web browser opens.
I
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interface
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A collection of related functions exposed by an object, and accessed through a unique interface ID.
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IRMA
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Interface RealMedia Architecture. RealSystem, also called RealMedia Architecture (RMA), is based on the Component Object Model (COM) jointly developed by Microsoft Corporation and Digital Equipment Corporation.
M
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MIME type
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Multipurpose Internet Mail Extension. A datatype specification originally used for mail messages and now generalized to identify datatypes delivered over the Internet.
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MISUS object
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The Multi-Instance Site User Supplier object, a default object instantiated by the client. When a renderer supports the "Wall of TVs" feature, it sends rendered data to this object as if it were the actual site. This object then passes the data to one or more sites.
N
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Network Services
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Services that provide cross-platform methods for managing network communications. Any server-side or client-side RealSystem component can use Network Services to create TCP or UDP connections for reading and writing data. Network Services also provides interfaces that let components resolve DNS host names and listen for TCP connections on specified ports.
O
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object
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A unique instance of a data structure defined according to the template provided by its class. Each object has its own values for the variables belonging to its class, and can respond to the methods defined by its class.
P
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packet
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A chunk of data delivered from a source to a rendering plug-in at a particular time during the playback of a stream.
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packet loss
-
The percentage of packets dropped during a RealSystem streaming presentation.
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plug-in
-
An executable that extends or enhances the operation of RealSystem. RealSystem server-side or client-side plug-ins use the same architecture.
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PNA
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A proprietary control protocol used by RealServer versions 3.0 through 5.0 to communicate with RealPlayer. RealServer G2 and RealPlayer G2 use the Real Time Streaming Protocol (RTSP) instead of PNA but support PNA for backward compatibility.
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preroll
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The amount of data in milliseconds a rendering plug-in requests before it receives its first time synchronization notification. The actual preroll is always equal to or greater than the value requested by the plug-in.
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presentation
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One or more RealSystem clips that are streamed from a server to a client.
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profile
-
A clip or group that can be rendered differently depending on the preferences of the client. For example, for the same video one client could choose a Japanese audio stream and another could choose a Spanish audio stream. In the SMIL file,
<switch>
statements list profile options.
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property
-
Information that helps RealServer stream packets associated with the rule intelligently. For example, the mandatory informational property "AverageBandwidth" tells RealServer the average bandwidth needed to stream packets of this rule effectively.
R
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RealAudio
-
A RealSystem datatype for streaming highly compressed audio over a network.
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RealFlash
-
A RealSystem clip type for streaming Shockwave Flash animation along with a RealAudio soundtrack.
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RealMedia
-
A blanket term used to refer to RealSystem G2 and the various "real" datatypes that it can stream.
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RealMedia Architecture (RMA)
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A client/server system developed by RealNetworks that gives content creators the ability to stream any data type.
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RealMedia File Format (RMFF)
-
A standard tagged file format that uses four-character codes to identify file elements. These codes are 32-bit, represented by a sequence of one to four ASCII alphanumeric characters, padded on the right with space characters. The datatype for four-character codes is
FOURCC
.
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RealPix
-
A RealSystem clip type (file extension
.rp
) for streaming still images over a network. It uses a mark-up language for creating special effects such as fades and zooms.
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RealPlayer
-
RealSystem client designed to play multimedia presentations streamed by RealServer G2 or a Web server.
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RealServer G2
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Server software developed by RealNetworks and based on the RealSystem G2 architecture. It provides robust streaming of many datatypes to RealSystem clients.
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RealSystem
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The system for streaming clips such as RealAudio and RealVideo over a network. It consists of RealServer G2, RealPlayer, and production tools.
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RealSystem client
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An application such as RealPlayer that consists of a top-level client and the client core. The top-level client supplies the user interface, communicating to the core and rendering plug-ins. The core handles data transport and provides features such as Audio Services.
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RealText
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A RealSystem clip type (file extension
.rt
) for streaming text over a network. It uses a mark-up language for formatting text.
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RealVideo
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A RealSystem data type for streaming video.
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registry
-
The RealServer property registry. This is separate from the Windows registry.
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Remote Broadcast Library
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A library of methods that ties an encoding application to RealServer's broadcast plug-in for live broadcast. The encoding application passes encoded data to the library, which then connects to a RealSystem broadcast plug-in. The plug-in delivers the stream to RealServer, which broadcasts it.
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RTSP
-
Real-Time Streaming Protocol. A protocol jointly developed by RealNetworks and Netscape Communications for streaming multimedia over IP networks. RTSP works with established protocols such as RTP and HTTP and can be implemented on client and server across multiple operating system platforms, including the Macintosh, Windows, and UNIX.
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rule
-
A set of properties and, optionally, an expression that helps RealServer transmit a group of packets intelligently. Each packet is associated with one rule. Rules are part of Adaptive Stream Management (ASM).
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rule book
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Used in Adaptive Stream Management (ASM), a set of rules that describes a media stream. Each stream has a rule book defined by its file format plug-in. The plug-in uses the stream header to send rules to the client, which subscribes to one or more of them based on properties such as its available bandwidth.
S
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site
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An object that receives rendered data for display. The client core supplies a site, and the rendering plug-in registers as a site user. The plug-in can then send data without providing platform-specific commands for data display.
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site user
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The object, typically the renderer, that "uses" a site by sending it display data.
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site user supplier
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An object, either the renderer or the "client core, that creates and destroys site user objects.
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slider
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A control found on RealPlayer that allows the user to scan forward or backward through a presentation.
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SMIL
-
Synchronized Multimedia Integration Language. A mark-up language for specifying how and when each clip plays. SMIL files use the extension
.smil
or .smi.
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source
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A file or live source of data, represented by a single URL, consisting of one or more streams of data.
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status code
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A value returned by RealSystem in response to a RealSystem function call. The header file pnresult.h defines the status codes used in many RealSystem function calls, as well as system error messages.
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stream
-
v. To send a media clip over a network so that it begins playing back as quickly as possible.
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n. A flow of a single type of data, measured in Kilobits per second (Kbps). A RealVideo clip's soundtrack is one stream, for example.
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subscribe
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To pick a rule from a rule book and receive packets associated with that rule. The client can subscribe to any number of rules at any time.
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SureStream
-
A technology that allows switching to a lower-bandwidth encoding in a RealAudio or RealVideo clip to compensate for network congestion. Available only in RealSystem G2.
T
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TestPlay
-
The core of RealPlayer G2 with a command line interface. Use Testplay to test streaming datatypes in a client environment other than RealPlayer. For example, use TestPlay to mimic the delivery of streaming data directly within a Web browser.
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top-level client
-
The part of a RealSystem client that supplies the user interface, communicating to the core and other components such as rendering plug-ins through RealSystem interfaces.
U
-
unsubscribe
-
To stop receiving packets for a rule.
W
-
windowed renderer
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A renderer that writes data to an operating system-specific site window through RealSystem. It can pass operating system-specific commands to the site.
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windowless renderer
-
A renderer that uses RealSystem to write operating system-generic data to a site. The site could be an operating system window or a "windowless" environment such as a browser. The renderer does not have specific knowledge of the display environment and does not pass operating system-specific commands to the site.
X
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XML
-
Extensible Mark-up Language. XML is simplified SGML (Standard Generalized Markup Language), the international standard for mark-up languages. XML allows you to create your own mark-up tags and is designed for use on the World Wide Web.
Copyright © 2000
RealNetworks
For technical support, please contact supportsdk@real.com.
This file last updated on 05/17/00 at 12:50:46.