信息技术 通用数字音频-可视系统 第6部分:信息表示

[中文适用范围]： ISO/IEC 16500 的这一部分采用实用的方法来规范信息表示。 仅指定了在生成DAVIC应用程序集时不能省略的信息类型（即广播、电影点播、家庭购物等）。 ISO/IEC 16500 这部分所采用的方法首先定义各种单媒体信息类型。 它们包括字符、文本、字体、服务信息、音频、视频和图形。 与 DAVIC 原则一致，为每种信息类型的编码选择一种工具。 多媒体组件包括一个或多个单媒体组件。 ISO/IEC 16500 的这一部分定义了多媒体信息编码和交换的方式。 这包括虚拟机和一组 API 的定义，以支持程序代码的互操作交换。 最后，ISO/IEC 16500 的这一部分定义了用于内容解码的参考解码器模型，该模型提供了对内容的约束。 该模型解决的主要问题是通过指定假设的 STU 内容解码的内存和行为约束来确保应用程序的互操作性，而不指定 STU 的内部设计。 根据参考解码器模型构建的应用程序将是“符合 ISO/IEC 16500 的应用程序”，并将在符合 ISO/IEC 16500 的 STU 上成功执行。 对于每个单媒体和多媒体组件，还指定了编码格式作为组件编码的适用约束。 单一媒体组件分为三种类型。 包含在其他单一媒体组件中的单一媒体组件（例如文本中的字符）是隐含类型的。 播放时不需要与时基同步的非隐含单媒体组件属于独立类型。 最后，其呈现可能需要与时基同步的非隐含单媒体组件是流类型。 ISO/IEC 16500 的这一部分定义了每个 DAVIC 定义的单媒体组件可以采用哪种类型，并指定流类型的单媒体组件的编码表示形式打包在 PES 数据包中（有关 PES 数据包的定义，请参阅 ISO/IEC 13818-1） 。 PES 数据包允许 (1) 包含时间戳以支持多个单媒体组件参考公共时基的相互同步，以及 (2) 在内容解码的公共参考模型中定义定时和缓冲区行为。 虽然有多种方法可以将单媒体和多媒体组件传送到 STU，但 ISO/IEC 16500 的这一部分定义了如何在 MPEG-2 传输流中携带这些组件。 DAVIC 指定了许多不同的配置文件。 在特定配置文件中，可能支持单媒体组件的子集。 每个符合 DAVIC 特定配置文件的 STU 应能够解码和呈现该配置文件中允许的每个单媒体和多媒体组件。 ISO/IEC 16500 的这一部分还规定了内容和元数据的打包方法。 打包内容以供传送的方式独立于将内容数据传送到 SPS 的方式（它可以在物理介质上或通过传输系统传送到服务提供商）。 所有节目内容在 DAVIC 系统中均表示为多媒体组件。 多媒体组件包括与单媒体组件之间的逻辑关系耦合的一个或多个单媒体组件。 多媒体组件将由内容提供商创建以输入到服务器。 [外文原描述]： This part of ISO/IEC 16500 takes a practical approach to the specification of Information Representation. Just the information types that cannot be dispensed with in producing the set of DAVIC applications (viz. broadcast, movies on demand, home shopping, etc.) are specified. The approach taken in this part of ISO/IEC 16500 starts by defining the various monomedia information types. They include character, text, fonts, service information, audio, video, and graphics. Consistent with DAVIC principles, one tool is selected for the encoding of each information type. Multimedia components comprise one or more monomedia components. This part of ISO/IEC 16500 defines the way in which multimedia information is coded and exchanged. This includes the definition of a virtual machine and a set of APIs to support interoperable exchange of program code. Finally, this part of ISO/IEC 16500 defines a Reference Decoder Model for contents decoding which provides constraints on content. The major problem addressed by the model is to ensure interoperability of applications by specifying memory and behaviour constraints for contents decoding by a hypothetical STU, without specifying the internal design of an STU. An application built according to the reference decoder model will be an "ISO/IEC 16500 conforming application" and will successfully execute on a STU that is compliant to ISO/IEC 16500. For each monomedia and multimedia component the coding format is specified, as well as applicable constraints for coding of the components. Three types of monomedia components are distinguished. Monomedia components which are included within other monomedia components, such as characters within text, are of type implied. Non-implied monomedia components that do not require synchronization with a time base at play back, are of type stand-alone. Finally, non-implied monomedia components of which the presentation may require synchronization with a time base are of type stream. This part of ISO/IEC 16500 defines which type each DAVIC defined monomedia component may take, and specifies that the coded representation of monomedia components of type stream are packetized in PES packets (for definition of PES packets refer to ISO/IEC 13818-1). PES packets permit (1) to include time stamps to support mutual synchronisation of multiple monomedia components in reference to a common time base and (2) to define timing and buffer behaviour in a common reference model for contents decoding. While there are various ways to deliver the monomedia and multimedia components to the STU, This part of ISO/IEC 16500 defines how the components are carried in an MPEG-2 Transport Stream. DAVIC specifies a number of different profiles. In a specific profile there may be support of a subset of the monomedia components. Each STU that complies to a specific profile of DAVIC shall be capable of decoding and presenting each monomedia and multimedia component permitted within that profile. This part of ISO/IEC 16500 also specifies methods for packaging of contents and metadata. The way in which content is packaged for delivery is independent of the way in which content data is delivered to the SPS (it may be delivered to a Service Provider either on physical media or over a transmission system). All programming content is represented in the DAVIC system as multimedia components. Multimedia components comprise one or more monomedia components coupled with the logical relationships between the monomedia components. The multimedia components will be created by content providers for input to the servers.