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6.4. XMT-Ω FORMAT

The goals of the XMT-Ω format are to provide ease of use for content creation, to facilitate content exchange between authors and authoring tools, and to provide a content representation that is compatible and interoperable with SMIL 2.0 [SMIL01].

In MPEG-4, objects are represented as nodes in a scene graph, with some nodes connected to audio or visual ESs, with their interactive behaviors described using a routing mechanism that connects two fields together from an event output to an event input (see Chapter 4). The XMT-Ω format describes audiovisual objects and their relationships at a higher level, wherein content requirements are expressed in terms of the author's intent, using media, timing, and animation abstractions, rather than by coding explicit node and route connections. These higher-level constructs facilitate, among other aspects, content exchange between authors and authoring tools and also content repurposing. An authoring tool would compile XMT-Ω into MPEG-4 content by mapping these constructs into BIFS, ODs, media streams, and so on, along with any appropriate audio or visual media compression or conversions that may be required. Media sources can be of a variety of formats native to the machine on which the authoring tool is executing, and it is the responsibility of the tool, during the compilation phase, to convert media to suitable target formats for MPEG-4, using appropriate bit rates and so on.


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