| Advanced Systems Format | |
|---|---|
 This image illustrates the computer icons thatWindows Vista displays for Advanced Systems Format, depending on the file name extension. From left to right, the icons correspond to.asf,.wma, and.wmv files. | |
| Filename extension | .asf .wma .wmv |
| Internet media type | video/x-ms-asf, application/vnd.ms-asf[1] |
| Type code | 'ASF_' |
| Uniform Type Identifier (UTI) | com.microsoft.advanced-systems-format |
| Magic number | 30 26 B2 75 8E 66 CF 11 A6 D9 00 AA 00 62 CE 6C[2] |
| Developed by | Microsoft |
| Initial release | Proprietary: 16 September 1996; 29 years ago (1996-09-16)[3][4] Public: 26 February 1998; 27 years ago (1998-02-26)[5] |
| Latest release | 01.20.03 December 2004; 21 years ago (2004-12) |
| Type of format | Container format |
| Container for | Windows Media Audio,Windows Media Video,VC-1 |
| Open format? | Yes |
| Free format? | No[6] |
Advanced Systems Format (formerlyAdvanced Streaming Format,Active Streaming Format) isMicrosoft'sproprietarydigital audio/digital videocontainer format, especially meant forstreaming media. ASF is part of theMedia Foundation framework.
ASF is based onserializedobjects which are essentiallybyte sequences identified by aGUID marker.
The format does not specify how (i.e. with whichcodec) the video or audio should be encoded; it just specifies the structure of the video/audio stream. This is similar to the function performed by theQuickTime File Format,AVI, orOgg formats. One of the objectives of ASF was to support playback fromdigital media servers,HTTP servers, and local storage devices such ashard disk drives.
The most common media contained within an ASF file areWindows Media Audio (WMA) andWindows Media Video (WMV). The most common file extensions for ASF files are extension.WMA (audio-only files using Windows Media Audio, with MIME-typeaudio/x-ms-wma) and.WMV (files containing video, using the Windows Media Audio and Video codecs, with MIME-typevideo/x-ms-asf). These files are identical to the old.ASF files but for their extension and MIME-type. The different extensions are used to make it easier to identify the content of a media file.[7]
ASF files can also contain objects representingmetadata, such as the artist, title, album and genre for an audio track, or the director of a video track, much like theID3 tags ofMP3 files. It supports scalable media types and stream prioritization; as such, it is a format optimized for streaming.
The ASF container provides the framework fordigital rights management in Windows Media Audio and Windows Media Video. An analysis of an older scheme used in WMA reveals that it is using a combination ofelliptic curve cryptography key exchange,DES block cipher, a custom block cipher,RC4 stream cipher and theSHA-1 hashing function.
ASF container-based media are sometimes still streamed on the internet either through theMMS protocol or theRTSP protocol. Mostly, however, they contain material encoded for 'progressive download', which can be distributed by any webserver and then offers the same advantages as streaming: the file starts playing as soon as a minimum number of bytes is received and the rest of the download continues in the background while one is watching or listening.
TheLibrary of Congress Digital Preservation project considers ASF to be thede facto successor ofRIFF.[2] In 2010Google picked RIFF as the container format forWebP.
The specification is downloadable from the Microsoft website,[8] and the format can be implemented under alicense from Microsoft that however does not allow distribution of sources and is not compatible withopen source licenses. The author of the free software projectVirtualDub reported that a Microsoft employee informed him that his software violated a Microsoft patent regarding ASF playback.[9]
Certainerror-correcting techniques related to ASF were patented in the United States (United States Patent 6,041,345 Levi, et al. March 21, 2000) by Microsoft until August 10, 2019.
