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ASF

Video Format Description

ASF is the file extension for Advanced Streaming Format, an open file format for streaming multimedia files. This extensible format was developed by Microsoft as a container format able to store audio, video, text, graphics, and animation content compressed with a variety of codecs, and transmit them over networks. ASF does not define any of the formats within the file, but just the standardized container format. ASF is part of the Windows Media framework.

An ASF file consists of three main sections, or objects. The first is the Header, which contains basic information such as file size, the codec used, and the number of data streams included. The metadata is also in the Header. The metadata contains such information as title of the file, name of the album, the genre of the track (if an audio file) and the director of the file (in case of a video file). The second object is the Data. This contains the stream data in the form of packets. The third object, the Index, contains a list of key-frame pairs. This list makes it easy for the application to go through it and recognize the files.

The main advantage of an ASF file is that playback is possible on a wide variety of applications such as different types of servers (e.g. HTTP and digital media servers) and local storage devices (e.g. hard disks and CDs). Other benefits include support of scalable audio, video, and other data; provides a means to share one multimedia file easily over different range of bandwidths; create multimedia files independent of operating system and communication protocol; and control of stream relationships in multimedia files.

Another important feature of the ASF file is its ability to be read even if the complete file is not downloaded due to some data problem or error. This is possible because of the GUIDs (Globally Unique Identifiers), which are placed at the beginning of each section, or object, of an ASF file. These GUIDs enable transmission of objects in any order and still be readable.

ASF files are supported by Windows Media Player and VideoLAN VLC media player over all platforms.