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Overview of the ASF Format

The Advanced Systems Format (ASF) is an extensible file format designed primarily for storing and playing synchronized digital media streams and transmitting them over networks. ASF is the container format for Windows Media Audio and Windows Media Video-based content. The extension wma or wmv is used to specify an ASF file that contains content encoded with the Windows Media Audio and/or Windows Media Video codecs. The Windows Media Format SDK can be used to create and read Windows Media files, as well as ASF files that contain other types of compressed or uncompressed data.

This section provides a general description of the ASF format as background information. Because the reader and writer objects handle all low-level file parsing and formatting tasks, it is not necessary to have a detailed understanding of ASF before using this SDK to create ASF files. The complete ASF specification can be found on the Microsoft Web site.

The primary goals of the ASF format are:

  • To support efficient playback from media servers, HTTP servers, and local storage devices.
  • To support scalable media types such as audio and video.
  • To permit a single multimedia composition to be presented over a wide range of bandwidths.
  • To allow authoring control over media stream relationships, especially in constrained-bandwidth scenarios.
  • To be independent of any particular multimedia composition system, computer operating system, or data communications protocol.

An ASF file can contain multiple independent or dependent streams, including multiple audio streams for multichannel audio, or multiple bit rate video streams suitable for transmission over different bandwidths. The streams can be in any compressed or uncompressed format; however, the best compression is achieved with the Microsoft Windows Media Audio and Video 9 Series codecs. In addition to the standard audio and video media stream types, an ASF file can also contain text streams, Web pages and script commands, and any other arbitrary data type. ASF supports live and on-demand multimedia content. It can be used as a vehicle to record or play back H.32X (for example, H.323 and H.324) or MBONE conferences.

An ASF file is organized into sections called "objects."  There are three top-level objects, a Header object and a Data object (both required), plus an optional Index object. The Header object contains general information about the file, such as file size, number of streams, error correction methods, and codecs used. Metadata is also stored here. The Header object is the only top level object that can contain other objects. The Data object contains the stream data, organized in packets. The Simple Index object contains a list of associated timestamp–key frame pairs that enables applications to seek through a file efficiently.

Each top-level or lower-level object begins with a globally unique identifier (GUID) and a size value. These numbers allow the file reader to parse the information at appropriate places into identifiable objects. Because of these GUIDs, lower-level objects can be sent in any order and still be recognized. The ASF format is designed to overcome inaccurate data reception. A partially downloaded ASF file can still be read, as long as it contains the Header object and at least one Data object.

The following diagram shows the objects that make up an ASF file. Shaded objects are optional. Certain objects, such as the Stream Properties object, can have multiple instances.

Diagram showing the objects that make up an ASF file.




高级媒体系统格式(The Advanced Systems Format) 主要是为存储、同步播放、通过网络传输数字多媒体流信息而设计的一套可以扩展的文件

格式。ASF是一个用来存储windows音频和视频信息的包装格式(Container format)。扩展名wma和wmv是用来标识此ASF文件是由windows多媒体

音频或视频编码器压缩而成的。Windows Media Format SDK可以用来创建和读取Windows多媒体信息文件,也可以很好的读取其它的经过压缩的


本部分主要讲述一下ASF格式的基本的背景信息。因为有读取器和写入器处理所有底层的分析和格式化任务,所以当你用Windows Media Format

SDK创建ASF的时候没有必要深入理解ASF的具体信息(译者注:实践证明,越不了解越晕)。完整详尽的ASF规范可以在 找到。


用来支持从媒体服务器(windows media server),http服务器或本地存储设备取得数据,并实时播放。
To permit a single multimedia composition to be presented over a wide range of bandwidths.
To allow authoring control over media stream relationships, especially in constrained-bandwidth scenarios


流。这些媒体流可以是任何经过压缩或没有压缩的格式。不管怎么说M$的Windows Media Audio 和Video 9 Series 编码/解码器提供了最好的


媒体信息。它可以用来担当记录和播放H.32X(例如:h.323 和h.324)或MBONE会议的传播媒体。









re: overview of the ASF Format(ASF格式概述译文)


re: overview of the ASF Format(ASF格式概述译文)
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re: overview of the ASF Format(ASF格式概述译文)