Advanced Systems Format
{{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{{cite web|url=https://www.iana.org/assignments/media-types/application/vnd.ms-asf|publisher=IANA|year=1997|author=Microsoft|author-link=Microsoft|title=Registration of MIME media type application/vnd.ms-asf|website=iana.org}}
| magic = 30 26 B2 75 8E 66 CF 11
A6 D9 00 AA 00 62 CE 6C{{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)}}
| standard =
| url =
| type code = 'ASF_'
| uniform type = com.microsoft.advanced-systems-format
| owner = Microsoft
| type = 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}}{{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}}{{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}}
Public: {{start date and age|1998|02|26|df=y}}{{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}}
| latest_release_version = 01.20.03
| latest_release_date = {{start date and age|2004|12|df=y}}
| open = Yes
}}
Advanced Systems Format (formerly Advanced Streaming Format, Active Streaming Format) is Microsoft's proprietary digital audio/digital video container format, especially meant for streaming media. ASF is part of the Media Foundation framework.
Overview and features
ASF is based on serialized objects which are essentially byte sequences identified by a 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, AVI, or Ogg formats. One of the objectives of ASF was to support playback from digital media servers, HTTP servers, and local storage devices such as hard disk drives.
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 audio/x-ms-wma
) and {{samp|.WMV}} (files containing video, using the Windows Media Audio and Video codecs, with MIME-type video/x-ms-asf
). 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.{{Cite web|url=http://support.microsoft.com/kb/284094|title=The Difference Between ASF and WMV/WMA Files}}
ASF files can also contain objects representing 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, DES block cipher, a custom block cipher, RC4 stream cipher and the SHA-1 hashing function.
ASF container-based media are sometimes still streamed on the internet either through the MMS protocol or the 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 RIFF. In 2010 Google picked RIFF as the container format for WebP.
License
The specification is downloadable from the Microsoft website,{{Cite web|url=http://download.microsoft.com/download/7/9/0/790fecaa-f64a-4a5e-a430-0bccdab3f1b4/ASF_Specification.doc|title=ASF Specification Download}} 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 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.{{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 }}
Certain 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
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]
- [http://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}}
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Category:Digital container formats