ASF File Extension: An Overview

ASF File Extension: Introduction

Advanced Systems Format (ASF) is an extensible file format developed by Microsoft to help developers save, play and transmit streaming digital media files over networks. ASF is part of the Windows Media framework and is based on the Microsoft’s proprietary digital audio/digital video container format. Windows Media Audio (WMA) and Windows Media Video (WMV) are the two most common file formats that are contained within an ASF file.

ASF File: Benefits

ASF files support and enable playback from different types of servers such as HTTP servers and digital media servers and other local storage devices, such as hard disks and CDs. These files support scalable media types, such as audio and video data and they enable you to share one multimedia file easily over different range of bandwidths. You can use ASF technology to develop multimedia files that are independent of operating system, communication protocol and multimedia composition system. The ASF format also enables in controlling stream relationships in multimedia files, which is especially useful in conditions where there are constraints over bandwidth.

ASF files can contain both independent and dependent data streams that can be either in compressed or uncompressed form. These files can include multiple bit rate video media streams that can be transmitted over wide range of bandwidths and multiple audio media streams to be used for multichannel audio transmission. ASF files are not limited to audio-video data streams. They can also contain other arbitrary data types, such as script commands, Web pages, JPEG images, and binary and other data streams.

ASF File: Structure

An ASF file, basically, comprises multiple sections referred to as objects. At the top level there are three objects, Header, Data, and Index. Out of these three, Header and Data objects are essential whereas the Index object is optional.

Header Object: This object comprises basic information about your ASF file-size of the files, codecs used, methods used for error correction, and number of data streams included. The Header object also contains the metadata of the file. In this metadata, you can store information such as title of the file, name of the album, and genre of the track-if it is an audio file and director of the track-if it is a video file. At the top level of ASF file, the Header is the only object that can contain other objects within it.

Data Object: Stream data is stored in the data object in the form of packets.

Index Object: This object comprises of a list of key-frame pairs that make it easy for applications to go through the files. This index object may contain information such as time of presentation, frame number of a video and a reference time stamp.

ASF files are designed by keeping in mind the problems associated with incorrect data download. This is the reason why all ASF objects both at top-level or lower-level start with a GUID (Globally Unique Identifier) and a size value. These GUIDs enable transmission of lower-level objects in any order and still be readable. Therefore, when an ASF file is downloaded, an ASF file reader can parse the downloaded file at multiple places into readable objects. Now, if due to some problem, you are unable to download the entire file, the file may still be readable if it comprises the Header object and at least one Data object.

ASF files are supported by Windows Media Player that is shipped with your Windows system. In certain versions of Windows Media Player there are a few security vulnerabilities that may cause problems while processing ASF file. You can fix this problem by downloading and installing a patch for your version of Windows Media Player and operating system from the Microsoft Support Website.