What is ASF?

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.

Goals:

1- To support efficient playback from media servers, HTTP servers, and local storage devices.

2- To support scalable media types such as audio and video.

3- To permit a single multimedia composition to be presented over a wide range of bandwidths.

4- To allow authoring control over media stream relationships, especially in constrained-bandwidth scenarios.

5- To be independent of any particular multimedia composition system, computer operating system, or data communications protocol.

Objects:

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.

1- Header object: It 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.

2- Data object: Containing the stream data, organized in packets.

3- Optional Index object: This one contains a list of associated index/key-frame pairs that enable applications to seek through a file efficiently. The index associated with each key frame can be a presentation time, a video frame number, or a reference time stamp.

Related Software:

Macgo Mac Blu-ray Player: Play ASF format on your Mac.
Macgo Windows Blu-ray Player: Play ASF on Windows platforms.
Macgo Free Mac Media Player: Play ASF for Mac OS X.

Related Source:

Visit Advanced Systems Format on Wikipedia.
An overview of the ASF format.