Sustainability of Digital Formats: Planning for Library of Congress Collections

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ASF (Advanced Systems Format)

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Advanced Systems Format (ASF)
Description File format that wraps various content bitstreams; data types can include audio, video, script command, JPEG-compressed still images, binary, and other streams defined by developers. This description is focused on the use of the format for audio and video.
Production phase Typically a final state format for enduser delivery; may be used as a middle-state format, e.g., the video source when producing lower-resolution streaming versions.
Relationship to other formats
    Has subtype WMA, Windows Media Audio. File format.
    Has subtype WMV, Windows Media Video. File format
    Has subtype ASF files containing streams of other types and/or produced by other codecs, not documented at this time.

Local use Explanation of format description terms

LC experience or existing holdings None
LC preference

For audio, WAVE_LPCM is preferred.

For file-based compressed video, bitstreams encoded as MPEG-2 (various profiles, the higher the better) or MP4-FF_2 (MPEG-4, various encodings and profiles, the higher the better) are preferred.

For uncompressed or losslessly compressed video, which is generally preferred to lossy compressed, MXF may be preferred as a wrapper; this topic will be developed in a future investigation.

Sustainability factors Explanation of format description terms

Disclosure Fully documented. Proprietary format developed by Microsoft.
    Documentation Advanced Systems Format (ASF) Specification; as of February 4, 2014, the PDF and XPS files downloadable were for revision 01.20.06, May, 2012. December 2004 specification is available as HTML page. Both links point to archived documents in the Internet Archives' Wayback Machine.
Adoption WMA appears to be widely adopted; the compilers of this document do not know the extent of adoption of WMV.
    Licensing and patents Licensed by Microsoft (link available through Internet Archive); fees are for use of tools to create content or for the provision of decoders to endusers, not per use or per unit distributed.
Transparency The ASF wrapper is transparent. Regarding the transparency of the codecs that may be contained, see: WMA9, WMA9_PRO, WMA9_LL, WMV9, and WMV9_PRO.

Metadata is contained in Header Objects, consisting of many types of subobjects for various kinds of technical metadata. Producers may also include a Content Description Object for "bibliographic" metadata, including "Author", "Title", "Copyright", "Description", and "Rating." Other objects may be used to extend this description and for information about digital rights management and other purposes.

ASF uses an extensible set of GUIDs (Globally Unique IDentifiers) to identify all objects and entities within ASF files, including media types, codec types, error correction approaches, and other elements.

External dependencies None
Technical protection considerations The Content Encryption Object within the header lets authors protect content by using Microsoft Digital Rights Manager version 1. The Extended Content Encryption Object lets authors protect content by using the Windows Media Rights Manager (link available through Internet Archive) Software Development Kit (SDK). Using this tool, encrypted digital media files can be set to require the acquisition of a license containing a key before the the content can be played.

Quality and functionality factors Explanation of format description terms

Moving Image
Normal rendering Good support.
Clarity (high image resolution) Depends on codec used for bitstream.
Functionality beyond normal rendering Supports content types beyond audio and video. Can be used with SAMI (Microsoft Synchronized Accessible Media Exchange), a captioning format that the Windows Media Player interprets in order to present text synchronized with audio and video (and other content forms).
Normal rendering Good support.
Fidelity (high audio resolution) Depends on codec used for bitstream.
Multiple channels Depends on embedded bitstream.
Support for user-defined sounds, samples, and patches Depends on embedded bitstream.
Functionality beyond normal rendering See Moving Image factors above.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension asf
For files that do not contain Windows Media-based bitstreams. Note that wma is specified for WMA, Windows Media Audio, and wmv for WMV, Windows Media Video. Both wma and wmv have their own Internet Media Type designators and unique ASF GUIDs.
Internet Media Type application/
From IANA. Also in LC implementation of Apache mime.types.
Internet Media Type audio/asf
Selected from The File Extension Source.
Magic numbers Hex: 30 26 B2 75 8E 66 CF 11 A6 D9 00 AA 00 62 CE 6C
ASCII: 0&²u.fÏ.¦Ù.ª.bÎl
For extension asf; from Gary Kessler's File Signatures Table.
ASF GUID See note.  Globally Unique IDentifiers that vary according to the element or feature included in the file; see the Advanced Systems Format (ASF) Specification (link available through Internet Archive), Section 10, pp. 88 ff. Specification also available as HTML page.

Notes Explanation of format description terms

History The format was initially developed to support streaming media, and commentators report that ASF originally stood for Advanced Streaming Format. As potential uses went beyond streaming, it came to be called Advanced Systems Format, and it appears to function more or less as a successor-replacement for RIFF.

Format specifications Explanation of format description terms

Useful references


Last Updated: 08/04/2021