Requirements

The resource management of a real-time system schedules the access of  tasks to system resources. A task is defined as a schedulable system entity such as a thread or a process, and is characterised by its time constraints and resource requirements. The timeliness of the media presentations or manipulations performed by a task is as crucial as the correctness of the operation.

The aim of a processor resource's management component is to calculate a schedule that allows the timely processing of as many time-critical tasks as possible. A real-time multimedia scheduler must take into account externally defined time constraints as well as time limits imposed by internal data dependencies.

The real-time requirements of multimedia applications are usually---depending on the application type---less demanding than those of traditional command and control systems, which often have a direct physical impact:

• Multimedia systems are usually more fault tolerant than command and control systems.
• While missing a deadline is not desirable, it generally does not have severe physical consequences.
• Continuous media data is most often the result of the periodic sampling of a signal. Hence, tasks require the processor resource periodically; such tasks are much easier to schedule than sporadic tasks.
• The bandwidth demand can often be adjusted dynamically to the available capacities. This is known as  media scaling.