Time-Based Media Representation and Delivery

Time-Based Media Representation and Delivery
Temporal relationships are a characteristic feature of multimedia objects. Continuous media objects such as video and audio have strict synchronous timing requirements. Composite objects can have arbitrary timing relation-ships. These relationships might be specified to achieve some particular visual effect of sequence. Several different schemes have been proposed for modeling time-based media. These are reviewed and evaluated in terms of representational completeness and delivery techniques.
Introduction
Multimedia refers to the integration of text, images, audio, and video in a variety of application environments. These data can be heavily time-dependent, such as audio and video in a motion picture, and can require time-ordered presentation during use. The task of coordinating such sequences is called multimedia synchronisation or orchestration. Synchronisation can be applied to the playout of concurrent or sequential streams of data and also to the external events generated by a human user. Consider the following illustration of a newscast shown in Figure 1.14. In this illustration multiple media are shown versus a time axis in a timeline representation of the time-ordering of the application.
Temporal relationships between the media may be implied, as in the simultaneous acquisition of voice and video, or may be explicitly formulated, as in the case of a multimedia document which possesses voice annotated text. In either situation, the characteristics of each medium and the relationships among them must be established in order to provide coordination in the presence of vastly different presentation requirements In addition to simple linear playout of time-dependent data sequences other modes of data presentation are also viable and should be supported by a multimedia information system (MMIS). These include reverse, fast forward, fast-backward, and random access. Although these operations are quite ordinary in existing technologies (e.g., VCRs), when nonsequential storage, data compression, data distribution, and random communication delays are introduced, the provision for these capabilities can be very difficult.