Nested Context Language (NCL) is the declarative language of the Brazilian Terrestrial Digital TV System. NCL is part of ISDB (International Standard for Digital Broadcasting) standards and also the ITU-T Recommendation H.761 for IPTV services. This paper presents, discusses, and illustrates the NCL hierarchical control model for multiple exhibition device support. Based on this model, multiple devices are orchestrated to run a DTV application in cooperation. Two types of multiple device exhibitions are distinguished. Those where the same content is shown in a set of devices under a unique control, and those where content is under each individual device control, working completely independent. In this last case, depending on viewer interactions, the resulting presented content can differ from a device to another. Examples of NCL applications using both options are presented and discussed.

Intermedia synchronization is related with spatial and temporal relationships among media objects that compound a DTV application. From the server side (usually a broadcaster's server or a Web Server) to receivers, end-to-end intermedia synchronization support must be provided. Based on application specifications, several abstract data structures should be created to guide all synchronization control processes. A special data structure, a labeled digraph called HTG (Hypermedia Temporal Graph) is proposed in this paper as the basis of all other data structures. From HTG, receivers derive a presentation plan to orchestrate media content presentations that make up a DTV application. From this plan other data structures are derived to estimate when media players should be instantiated and when data contents should be retrieved from a DSM-CC carousel or from a return channel. If the return channel provides QoS support, another data structure is derived from the presentation plan, in order to determine when resource reservation should take place. For content pushed by broadcasters, HTG is used in the server side as the basis for building the carousel plan, a data structure that guides the order and frequency that media objects should be broadcasted.

In some hypermedia system applications, like interactive digital TV applications, authoring and presentation of documents may have to be done concomitantly. This is the case of live programs, where not only some contents are not known a priori, but also some temporal and spatial relationships, among program media objects, may have to be established after the unknown content definition. This paper proposes a method for hypermedia document live editing, preserving not only the presentation semantics but also the logical structure semantics defined by an author. To validate this proposal, an implementation has been done for the Brazilian Digital TV System, which is also presented.

This paper proposes new features for presenting and authoring MPEG-4 programs using the NCL language. On one hand, the language allows to define relationships among objects inside an MPEG-4 scene and external media objects, including objects in other MPEG-4 scenes. Relationships with several different semantics will also be allowed other than those defined by the standard. An NCL hypermedia formatter integrated with MPEG-4 players supports these new introduced features. On the other hand, the paper also takes advantage of the NCL composite-node template concept, to add new authoring facilities when specifying MPEG-4 documents using the XMT-O language.