Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| 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. |
| 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. |
| Disclosure | Fully documented. Proprietary format developed by Microsoft. |
| Documentation | Advanced Systems Format (ASF) Specification; as of April 5, 2007, this was revision 01.20.03, December 2004. Some additional citations are provided in Useful references below. |
| Adoption | WMA appears to be widely adopted; the compilers of this document do not know the extent of adoption of WMV. |
| Licensing and patent claims | Licensed by Microsoft; 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 | See information on the codecs incorporated in ASF files: WMA9, WMA9_PRO, WMA9_LL, WMV9, and WMV9_PRO. |
| Self-documentation | 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 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. |
| Normal rendering | Good support. |
| Clarity (support for high image resolution) | Not applicable |
| Fidelity (support for high audio resolution) | Not applicable |
| Support for multiple sound channels | Not applicable |
| 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). |
| Tag type | 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/vnd.ms-asf | From IANA. Also in LC implementation of Apache mime.types. |
| Internet Media Type |
audio/asf video/x-ms-asf-plugin application/x-mplayer2 video/x-ms-asf video/x-ms-asf-plugin video/x-ms-wm video/x-ms-wmx | 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 | Globally Unique IDentifiers that vary according to the element or feature included in the file; see the Advanced Systems Format (ASF) Specification, pp. 88 ff. |
| General | |
| History | The format was initally 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. |
URLs
• Advanced Systems Format (ASF) Specification from Microsoft (as of April 5, 2007, this was revision 01.20.03, December 2004; http://www.microsoft.com/windows/windowsmedia/format/asfspec.aspx)
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URLs
• Overview of the ASF Format (http://msdn2.microsoft.com/en-us/library/aa390652.aspx)
• Architecture of Windows Media Rights Manager (http://www.microsoft.com/windows/windowsmedia/howto/articles/drmarchitecture.aspx)
• Windows Media Licensing (http://www.microsoft.com/windows/windowsmedia/licensing/licensing.aspx)
• IANA MIME Media Types (http://www.iana.org/assignments/media-types/)
• Gary Kessler's File Signatures Table (http://www.garykessler.net/library/file_sigs.html)
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