信息技术.计算机图形和图像处理.对多媒体对象的表示环境(PREMO).第3部分:多媒体系统服务

[中文适用范围]： ISO/IEC 14478 的这一部分定义了多媒体系统服务的标准集，可供多媒体应用程序开发人员在各种计算环境中使用。 重点是在异构、分布式计算环境中启用多媒体应用程序。 在 ISO/IEC 14478 的这一部分中，该组件也称为“多媒体系统服务”，缩写为 MSS。 多媒体系统服务构成了“中间件”框架——位于通用操作系统和特定应用程序之间的系统软件组件。 作为中间件，多媒体系统服务将较低级别的系统资源编组到支持多媒体处理的任务，提供一组可供多媒体应用程序开发人员使用的公共服务。 多媒体系统服务包含以下特征： a) 为媒体处理节点提供抽象类型，可通过子类型扩展以支持真实的媒体处理硬件或软件的抽象； b) 为数据流路径或媒体处理节点之间的连接提供抽象类型，进行封装；低级连接和传输语义； c) 将多个处理节点和连接分组为单个单元，以实现资源预留和流控制； d) 提供媒体数据流抽象，支持各种位置、时间和/或同步功能； e) 将媒体格式抽象与数据流抽象分离； f) 同步异常和异步事件； g) 应用对象能力的可见表征； h) 按位置和功能注册分布式环境中的对象； i) 通过位置和约束检索分布式环境中的对象； j) 定义媒体流协议以支持媒体独立传输和同步。 多媒体系统服务依赖于 ISO/IEC 14478-1（PREMO 基础）的对象模型以及 ISO/IEC 14478-2（PREMO 基础组件）中定义的对象类型和非对象数据类型。 [外文原描述]： This part of ISO/IEC 14478 defines a standard set of multimedia system services that can be used by multimedia application de­velopers in a variety of computing environments. The focus is on enabling multimedia applications in a heterogeneous, distrib­uted computing environment. Throughout this part of ISO/IEC 14478, this component will also be referred to as "Multimedia Systems Services", and abbreviated as MSS. The Multimedia Systems Services constitutes a framework of "middleware" - system software components lying in the region between the generic operating system and specific applications. As middleware, the Multimedia Systems Services marshals low­er-level system resources to the task of supporting multimedia processing, providing a set of common services which can be used by multimedia application developers. The Multimedia Systems Services encompasses the following characteristics: a) provision of an abstract type for a media processing node, extensible through subtyping to support abstractions of real media processing hardware or software; b) provision of an abstract type for the data flow path or the connection between media processing nodes, encapsulating low-level connection and transport semantics; c) grouping of multiple processing nodes and connections into a single unit for purposes of resource reservation and stream control; d) provision or a media dataflow abstraction. with support for a variety of position, time and/or synchronization capabili­ties; e) separation of the media format abstractions from the dataflow abstraction; f) synchronous exceptions and asynchronous events; g) application visible characterization of object capabilities; h) registration of objects in a distributed environment by location and capabilities; i) retrieval of objects in a distributed environment by location and constraints; j) definition of a Media Stream Protocol to support media independent transport and synchronization. The Multimedia Systems Services rely on the object model of ISO/IEC 14478-1 (Fundamentals of PREMO) and the object types and non-object data types defined in TSO/IEC 14478-2 (PREMO Foundation Component).