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{{Short description|File format}}
{{redirect-multi|4|.wmv|WMV file|.wma|WMA file|the video codec|Windows Media Video|the audio codec|Windows Media Audio}}
{{Infobox file format
| name = Advanced Systems Format
| icon = Computer icons of for ASF, WMA and WMV files.png
| icon_size = x64px
| iconcaption = {{midsize|This image illustrates the computer icons that [[Windows Vista]] displays for Advanced Systems Format, depending on the file name extension. From left to right, the icons correspond to {{mono|.asf}}, {{mono|.wma}}, and {{mono|.wmv}} files.}}
| extension = .asf .wma .wmv
| mime = video/x-ms-asf, application/vnd.ms-asf<ref>{{cite web|url=https://www.iana.org/assignments/media-types/application/vnd.ms-asf|publisher=[[Internet Assigned Numbers Authority|IANA]]|year=1997|author=Microsoft|author-link=Microsoft|title=Registration of MIME media type application/vnd.ms-asf|website=iana.org}}</ref>
| magic = 30 26 B2 75 8E 66 CF 11
A6 D9 00 AA 00 62 CE 6C<ref name="LoC">{{cite web |publisher=[[Library of Congress]]|work=Digital Preservation|date=2014-02-04|access-date=2014-03-12|url=http://www.digitalpreservation.gov/formats/fdd/fdd000067.shtml |title=ASF (Advanced Systems Format)}}</ref>
| standard =
| url =
| type code = 'ASF_'
| uniform type = com.microsoft.advanced-systems-format
| owner = [[Microsoft]]
| type = [[Container format (digital)|Container format]]
| container for = [[Windows Media Audio]], [[Windows Media Video]], [[VC-1]]
| contained by =
| extended from =
| extended to =
| released = Proprietary: {{start date and age|1996|09|16|df=y}}<ref>{{Cite web|title=Advanced Streaming Format|url=https://www.tech-insider.org/digital-video/research/1997/asf/index.htm|access-date=2021-12-13|website=Tech Insider}}</ref><ref>{{Cite news|date=1996-09-16|title=Microsoft Introduces NetShow, A Platform for Delivering Multimedia Content Over Intranets|url=https://news.microsoft.com/1996/09/16/microsoft-introduces-netshow-a-platform-for-delivering-multimedia-content-over-intranets/|access-date=2021-12-13|website=Microsoft Stories}}</ref><br/>Public: {{start date and age|1998|02|26|df=y}}<ref>{{cite IETF |title=Advanced Streaming Format (ASF) Specification |draft=draft-fleischman-asf-01 |last1=Fleischman |first1=Eric |date=26 February 1998 |publisher=Internet Engineering Task Force |access-date=13 December 2021}}</ref>
| latest_release_version = 01.20.03
| latest_release_date = {{start date and age|2004|12|df=y}}
| open = Yes
| free = No<ref>{{cite tech report |publisher=Library of Congress |location=Washington, D.C. |series=Sustainability of Digital Formats |type=Full draft |title=ASF (Advanced Systems Format) |date=6 April 2007 |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000067.shtml |access-date = 1 December 2021}}</ref>
}}

'''Advanced Systems Format''' (formerly '''Advanced Streaming Format''', '''Active Streaming Format''') is [[Microsoft]]'s [[Proprietary software|proprietary]] [[digital audio]]/[[digital video]] [[container format (digital)|container format]], especially meant for [[streaming media]]. ASF is part of the [[Media Foundation]] framework.

==Overview and features==
ASF is based on [[serialization|serialized]] ''[[Object-oriented programming|objects]]'' which are essentially [[byte]] sequences identified by a [[Globally Unique Identifier|GUID]] marker.

The format does not specify how (i.e. with which [[codec]]) 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 the [[QuickTime File Format]], [[Audio Video Interleave|AVI]], or [[Ogg]] formats. One of the objectives of ASF was to support playback from [[Streaming media|digital media servers]], [[HTTP server]]s, and local storage devices such as [[hard disk drive]]s.

The most common media contained within an ASF file are [[Windows Media Audio]] (WMA) and [[Windows Media Video]] (WMV). The most common file extensions for ASF files are extension {{samp|.WMA}} (audio-only files using Windows Media Audio, with MIME-type <code>audio/x-ms-wma</code>) and {{samp|.WMV}} (files containing video, using the Windows Media Audio and Video codecs, with MIME-type <code>video/x-ms-asf</code>). These files are identical to the old {{samp|.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.<ref>{{Cite web|url=http://support.microsoft.com/kb/284094|title=The Difference Between ASF and WMV/WMA Files}}</ref>

ASF files can also contain objects representing [[Metadata (computing)|metadata]], such as the artist, title, album and genre for an audio track, or the director of a video track, much like the [[ID3]] tags of [[MP3]] files. It supports scalable media types and stream prioritization; as such, it is a format optimized for streaming.

The ASF container provides the framework for [[digital 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 of [[elliptic curve cryptography]] key exchange, [[Data Encryption Standard|DES]] block cipher, a custom block cipher, [[RC4 cipher|RC4]] stream cipher and the [[SHA-1]] hashing function.

ASF container-based media are sometimes still streamed on the internet either through the [[Microsoft Media Services|MMS]] protocol or the [[Real Time Streaming Protocol|RTSP]] 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.

The [[Library of Congress]] Digital Preservation project considers ASF to be the ''de facto'' successor of [[Resource Interchange File Format|RIFF]].<ref name="LoC" /> In 2010 [[Google]] picked RIFF as the container format for [[WebP]].

==License==
The specification is downloadable from the Microsoft website,<ref>{{Cite web|url=http://download.microsoft.com/download/7/9/0/790fecaa-f64a-4a5e-a430-0bccdab3f1b4/ASF_Specification.doc|title=ASF Specification Download}}</ref> and the format can be implemented under a [[license]] from Microsoft that however does not allow distribution of sources and is not compatible with [[Open-source software|open source]] licenses. The author of the free software project [[VirtualDub]] reported that a Microsoft employee informed him that his software violated a Microsoft patent regarding ASF playback.<ref name="adv">{{citation |url=http://www.advogato.org/article/101.html |title=Advogato: Microsoft patents ASF media file format, stops reverse engineering |archive-url=https://web.archive.org/web/20170628194627/http://www.advogato.org/article/101.html |archive-date=2017-06-28 |access-date=2019-03-11 |url-status=dead }}</ref>

Certain [[Error detection and correction|error-correcting]] techniques related to ASF were patented in the United States ([https://patents.google.com/patent/US6041345A/ United States Patent 6,041,345] Levi, et al. March 21, 2000) by Microsoft until August 10, 2019.

==See also==
*[[Audio Video Interleave]] (AVI)
*[[Comparison of container formats]]

==References==
{{Reflist|2}}

==External links==
*[http://msdn.microsoft.com/en-us/library/ms983668(loband).aspx An Overview of Advanced Systems Format]
*[http://msdn.microsoft.com/en-us/library/dd757562(VS.85).aspx Overview of the ASF Format]
*[http://www.digitalpreservation.gov/formats/fdd/fdd000067.shtml Library of Congress analysis of ASF format sustainability]
*[https://avifile.sourceforge.net/docs.htm ASF Container Format - v2.0 (free available but unused) and v1.0 (reconstructed)]
*[http://msdn.microsoft.com/en-us/library/ms983653(loband).aspx MSDN How To Embed Windows Media Player in a HTML Web Page (For Webmasters)]
*[https://web.archive.org/web/20100315064515/http://www.microsoft.com/windows/windowsmedia/howto/articles/CustomizedExp.aspx Creating A Windows Media Custom Experience (For Webmasters)]

{{Compression formats}}
{{Internet Explorer}}

{{DEFAULTSORT:Advanced System Format}}
[[Category:Internet Explorer]]
[[Category:Digital container formats]]
[[Category:Microsoft Windows multimedia technology]]
[[Category:Digital rights management systems]]

Advanced Systems Format - Revision history

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