Sustainability of Digital Formats: Planning for Library of Congress Collections

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Advanced Authoring Format (AAF) Object, Version 1.1

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Advance Authoring Format (AAF) Object Specification, Version 1.1

Object-based file format that wraps metadata together with video, audio, and other bitstreams ("essences"), optimized for the interchange of content by creators ("authors") across platforms and between applications, generally intended for implementation in computer systems. Essences may also be external, e.g., a videotape.

Most commentators describe AAF as "wrapping all elements of a project for continued production or archiving" and "allowing for the expression of complex relationships between parts," while they describe the MXF subtype as "the 'digital equivalent of videotape,'" an allusion to tape's simple, linear structure. See the Notes for MXF for a comparison of AAF and MXF.

AAF metadata is stored in Mobs (Metadata objects) that are equivalent to packages in the MXF format; Mobs were called "packages" in earlier versions of AAF. CompositionMobs describe creative decisions on how to combine or modify essences, MasterMobs collect and may synchronize essence data, and provide indirect access to essences independent of storage details, File SourceMobs provide direct access to and describe essences, which may be stored as computer files, and Physical SourceMobs describe physical media such as a videotape or film. Packages similar to these exist in MXF, excepting CompositionMobs.

Mobs have one or more MobSlots that represent the passage of time, and are thus equivalent to MXF tracks: StaticMobSlots describe essences with no specific relationship to time, e.g., static text; TimelineMobSlots describe essence data that has a fixed or continuous relationship with time, e.g., video, audio, timecode; EventMobSlots describe essence data that has an irregular relationship with time, e.g., events controlled by signals sent to the GPI (General-Purpose Interface) port on various video devices.

Specifications for the AAF Stored Format and the AAF Low-Level Container describe the relationship of the format to Microsoft's Structured Storage specification; platform support, however, extends to Macintosh, Linus, Irix, and Solaris operating systems.

Production phase Initial-state for editing, or middle-state format for material exchange or archiving.
Relationship to other formats
    Has subtype MXF, Material Exchange Format
    May contain Various video, sound, and other essences (bitstreams), whose specific AAF associations are not documented at this time.
    Has earlier version AAF Object Versions 1.0 and 1.0.1, not documented at this time

Local use Explanation of format description terms

LC experience or existing holdings See preference note.
LC preference The Library's Packard Campus National Audio-Visual Conservation Center employs the MXF File, OP1a, Lossless JPEG 2000 in Generic Container subtype as the preservation master for reformatted video recordings.

Sustainability factors Explanation of format description terms

Disclosure Fully disclosed. Developed by the Advanced Authoring Format Association, founded in 2000 and renamed Advanced Media Workflow Association, Inc. (AMWA) in 2007.
    Documentation The object specification is titled Advanced Authoring Format (AAF) Object Specification v1.1 (2004-11-05). Related specifications are titled Advanced Authoring Format (AAF) Low-Level Container Specification v1.0.1 (2004) and Advanced Authoring Format (AAF) Stored Format Specification v1.0.1 (2004).
Adoption During the period 2000-2007, there was growing interest and some use of AAF. The main advocates were members of the (then) AAF Association, including hardware and software manufacturers (e.g., AVID and SONY), television companies (e.g., BBC and Turner networks), government (National Geospatial-Intelligence Agency [NGA], formerly the National Imagery and Mapping Agency [NIMA]), and movie studios (e.g., Warner Brothers). Adoption was enhanced by the availability of the open source AAF software developers kit (SDK). From about 2008 forward, industry interest has focused on extending the use of the MXF subtype (an SMPTE standard), especially through Application Specifications developed within the AMWA, the successor to the AAF Association.
    Licensing and patents None identified; see note on external dependencies below. A disclaimer on the AAF Object Specification cover sheet calls attention to "the possibility that implementation and compliance . . . may require the use of subject matter covered by patent rights." The AAF Low-Level Container Specification cover sheet includes this statement: "Certain patent rights holders have filed a statement of willingness to grant a patent license to all implementers of this specification desiring to obtain such a license, consistent with the requirements of the AAFA Intellectual Property Policy . . . . all negotiations regarding such terms and conditions must take place between the individual parties outside the context of the AAFA. Further information regarding those parties who have claimed patent rights in the specification and expressed their willingness to provide a license may be obtained from the AAFA Executive Director."
Transparency Wrapper is transparent; overall transparency depends upon the essence encoding. All video codecs depend upon algorithms and tools to read and will require sophistication to build tools.
Self-documentation Extensive metadata is required by or may optionally be placed in AAF files, although for the most part this is system or structural metadata, i.e., about the structure of the file, e.g., the relationship of parts, whether the essence is stored in little or big endian, index tables that provide information on the essence (display size, compression algorithm, the time line of a media clip, etc.), size of a sector, where a new partition starts, etc. The specification does not address the topic of intellectual or "bibliographic" metadata.

AAF is a binary format. In 2004, there was an effort under way to define AAF-X, an XML-schema-based representation of AAF metadata. The compiler of this format description is not aware of the outcome of this effort.
External dependencies Transparency
Technical protection considerations No information found. Since the format is used in initial- and middle-state environments (not for content distribution), protection technology may not be important at the level of the format itself.

Quality and functionality factors Explanation of format description terms

Moving Image
Normal rendering AAF files are not intended to play in the customary sense, although an AAF application that receives a composition Mob will "play" the content. AAF-capable applications are intended to support professional multimedia editing.
Clarity (high image resolution) Potentially excellent; depends upon the essence encodings selected.
Functionality beyond normal rendering Extensive in this authoring format, not documented here.
Normal rendering AAF files are not intended to play in the customary sense, although an AAF application that receives a composition Mob will "play" the content. AAF-capable applications are intended to support professional multimedia editing.
Fidelity (high audio resolution) Potentially excellent; depends upon encoding.
Multiple channels There appears to be no limit to the number of tracks; thus multiple sound tracks may be included.
Functionality beyond normal rendering Supports various features not documented here.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension aaf
From The File Extension Source.
Internet Media Type Not found.  Comments welcome.   
Magic numbers Not found.  Comments welcome.   
File signature {0x42464141, 0x000d, 0x4d4f,{0x06, 0x0e, 0x2b, 0x34, 0x01, 0x01, 0x01, 0xff}}
For StructuredStorages files with 512 byte sector size. The signature is the CLSID (class identifier) of the Root IStorage. From the AAF Stored Format Specification v1.0.1, p. 13.
File signature {0x0d010201, 0x0200, 0x0000,{0x06, 0x0e, 0x2b, 0x34, 0x03, 0x02, 0x01, 0x01}}
For StructuredStorages files with 4096 byte sector size. The signature is the CLSID (class identifier) of the Root IStorage. From the AAF Stored Format Specification v1.0.1, p. 13.

Notes Explanation of format description terms

General In 2005, the AAF Association Web site offered this mission statement: "The Advanced Authoring Format defines authoring as 'the creation of multimedia content including related metadata.' Today, content authoring usually involves opening source media, manipulating or editing the content and then resaving. AAF aims to remove cross platform project bottlenecks often hit when files are interchanged between applications. These include loss of project metadata, the need to rewrite whole files in order to edit them, limited off-line to on-line communication, poor referencing to other files and many other issues. In an ideal environment, a user would work with many different applications without worrying about interchange."

In a slide show delivered in 2002, Brad Gilmer, the executive director of the AAF Association, reported that the AAF software developers kit (SDK) was being extended by SONY to permit applications to read and write MXF files. Meanwhile, the AAF Association reports that they are beginning the development of an archiving protocol during 2005. Gilmer said that a protocol says, "use the AAF specifications 'this' way for 'this' application." After 2007, similar concepts were applied by AMWA (the successor organization) as it oversees the drafting of Application Specifications for MXF, the SMPTE-standardized AAF subtype.
History From the AAF Association Web site in 2005: "Incorporated in January 2000, the AAF Association, Inc. is a broadly-based trade association intended to promote the development and adoption of AAF technology throughout the media industry." The successor Advanced Media Workflow Assocation was established in 2007.

Format specifications Explanation of format description terms

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Last Updated: Tuesday, 14-Feb-2017 13:52:17 EST