A quality-of-service specification for multimedia presentations
Summary (2 min read)
1 Introduction
- The next section defines their terminology in terms of an architectural model for multimedia presentations.
- Sections 3 and 4 describe a data model for the specification of content and view respectively for a presentation.
[R,l]
- The Interval schema gives a start position and an interval extent.
- The authors use this information to specify both clipping intervals and linear transformations.
- This schema must contain the maximal set of dimensions for all output types.
- When used for audio specifications, the authors simply ignore the x and y intervals.
- The Space schema specifies intervals for t, x, and y coordinate dimension and a z interval for the output range.
start, end, duration: Content
- For a given content specification, the logical function returns a relation between a point in the logical output space and the acceptable output values for that point.
- Note that specifications reduce the set of acceptable values and where nothing is specified, all values are acceptable.
- Each cat construct specifies a single logical output with a sequence of clip constructs.
- Each clip specifies a portion of a transform construct and each transform construct defines the logical dimensions of a basic media source.
- This definition of content satisfies their goal of a data model for complex presentations except that the authors have no way to relate the logical content to actual presentation outputs.
[AudioDev, VideoDev]
- The logical dimensions in a content specification are generally not the same as the physical dimensions of the view.
- The Output schema declares a field tr that defines the transformation from logical to view output dimensions and a field clip that defines clipping bounds for view outputs.
- The clipping bounds for both audio and video match the full range of the transformed content.
- This asymmetry is necessary to preserve the content synchronization while allowing flexibility in the display of multiple logical outputs.
)) .(d,x,y,t,z)}
- The implementation of a presentation plan uniquely determines the value for every device at every point and time.
- The vVal function takes a VideoDev and integer values for the clock, X, and y coordinates, and returns the integer value at that pixel.
- The authors define a function actual that takes a particular presentation and returns a relation representing these output values.
- The authors are assuming that they can observe only one output value per clock tick and that the output value is constant over the duration of a clock cycle.
- The relation actual P and the relation ideal c v have the same type.
5 Quality Specification
- To calibrate this quality function to approximate user perception, the authors can adjust the values returned by the calib and synchCalib functions in the quality specification.
- When an error component equals the corresponding critical error value the quality is at most e-1 or approximately 0.37.
- The units for temporal shift, jitter, res, and synch are in seconds.
- Comparable values have been reported by other researchers for synchronization error [16] , but more experimentation is needed to determine how these values depend on the content, task, and the person who rates the quality.
6 Using Quality Specifications for Resource Reservation
- Analysis of a QOS specification can identify a range of presentation plans that might satisfy the specification as illustrated above.
- A multimedia player can perform this analysis automatically in response to playback requests.
- To guarantee that a particular presentation plan will satisfy a QOS specification a player must reserve resources for storage access, decompression, mixing, and presentation processes.
- The admission test may invoke resource reservation protocols for network and file system resources with resourcelevel QOS parameters derived from the process timing requirements.
- If the player can not find a presentation plan that both satisfies the QOS requirements and meets the admission test, then the QOS requirements must be renegotiated.
7 Conclusions
- The authors have implemented simple playback systems that make use of this QOS specification method.
- More work is planned to investigate algorithms for translating QOS specifications into feasible presentation plans.
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