The earliest playback time is the earliest time a

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Unformatted text preview: te representing objects, or a Petri net. For example, consider the multimedia scenario represented as an X-Y graph in Figure 19.15. It has four multimedia objects 0h 02, 03 and 04. St denotes the start point of object 0i. The same multimedia scenario is represented in Figure 19.16 as a petri net. Language-based Approach In this approach, the temporal relationships among the multimedia objects of a presentation scenario is represented in the form of a special programming language that has temporal synchronization functions. A few examples of synchronization functions that such a language may have are: 1. SyncAtomicSerial (A, B): Object B starts after object A stops. 2. SyncAtomicParallel (A, B): Objects A and B start simultaneously. 3. SynElemSerial (tl, A, t2, B): Object A starts after time tl, and object B starts after time t2 after A stops. 4. SyncElemParallel (tl, A, t2, B): Object A starts after time tl, and object B starts after time t2. Based on the values of tl and t2, objects A and B may overlap. Temporal Synchronization Note that temporal specification focuses only on the temporal relationships among the objects without explicit reference to time. Temporal synchronization mechanisms use the temporal relationships information of temporal specification and convert it into a set of playback schedules and retrieval schedules to enforce the playback deadlines for various multimedia objects of a presentation scenario. A playback schedule is the set of playback deadlines of multimedia objects in a multimedia scenario, where playback deadline of an object is the latest starting time of the object, for a meaningful presentation. Retrieval schedule is the set of request deadlines to the server. It accounts for end-to-end delays and ensures that the playback deadline is not missed. To display an object O at time Ts (the playback deadline), the presentation site sends a request to the corresponding media server at request time T r, which is R time units prior to Ts. R is the response time to account for possible experienced end-t...
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