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MHEG-5 overview

SInce MHEG-5 is the widest MHEG standard in operation and is widely known we will highlight this MHEG standard.

A multimedia application can be conceived as a set of self-contained objects based on synchronization and spatial-temporal relationships of multiple media formats, structural composition, event-action associations, navigation, and user interaction capabilities. Controlling the playback of time-dependent contents, like streams of multiplexed audiovisual data requires specific support. These streams demand VCR control functions (play, pause, fast forward, and so on), as well as the capability to manage events generated during their presentation. For example, rendering text subtitles can be synchronized with timecode events generated during the playback of a stream. MHEG-5 represents an application, as a set of scenes, which contain objects common to all scenes. A scene supports the spatially and temporally coordinated presentation of audiovisual content consisting of graphics, bitmaps, text, and streams (based on the multiplex of audio and video components). Interaction can be performed via graphic elements like buttons, sliders, text entry boxes, and hypertext selections. Every scene, as well as an entire application, is a self-contained entity that can represent its localized behavior by links that are event-action associations. Events can be generated by users, expiration of timers, playback of streams, and other conditions within the RTE.

The global scope of MHEG-5 is to define the syntax and semantics of a set of object classes that can be used for interoperability of multimedia applications across minimal-resources platforms. The developed applications will reside on a server, and as portions of the application are needed, they will be downloaded to the client. In a broadcast environment, this download mechanism could rely, for instance, on cyclic rebroadcasting of all portions of the application. It is the responsibility of the client to have a runtime that interprets the application parts, presents the application to the user, and handles the local interaction with the user.

The major goals of MHEG-5 are:

The MHEG-5 model is object-oriented. The actions are methods targeted to objects from different classes to perform a specific behavior and include:

To allow interoperability across heterogeneous systems, MHEG-5 specifies the precise encoding syntax. Two notations are possible: the ASN.1 notation, which MHEG-1 also adopts, and a textual notation as illustrated below:.

In a client-server architecture (Fig 8.2), MHEG-5 applications are stored on the server and downloaded to the terminal for the RTE to interpret. This model is not limited to storage and retrieval services. In the broadcast environment, for example, the set of channels transmitted on a broadcast network can be considered a virtual server, where the download mechanism relies on cyclic rebroadcast of all portions of an application.

MHEG Client-Server Interaction

next up previous
Next: MHEG Programming Principles Up: Multimedia and Hypermedia Information Previous: The family of MHEG
Dave Marshall