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 | Advance Authoring Format (AAF) Object Specification, Version 1.1 |
| Description | 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 Notes on the MXF description page 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. Many of these formats are described elswehere on this web site; see, for example, the video formats menu. |
| Has earlier versions | AAF Object Versions 1.0 and 1.0.1, not documented at this time |
| LC experience or existing holdings | None |
| LC preference | None at this time. It is likely that as preferences emerge, the Library will seek to identify preferred operational patterns (or what AAF calls protocols) that constrain the range of elements within an AAF instance. Investigation of this topic may also lead the Library to express a general preference for the MXF subtype, and one or more of its standardized operational patterns. |
| Disclosure | Fully disclosed. Developed by the Advanced Authoring Format Association. |
| 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 | There appears to be growing interest in AAF, an emerging community standard, although it may not be widely adopted at this time. The main advocate is the AAF Association, whose membership includes 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 is enhanced by the availability of the open source AAF software developers kit (SDK). |
| Licensing and patent claims | 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; as of 2004, there was an effort under way to define AAF-X, an XML-schema-based representation of AAF metadata; the AAF Association documents on this topic are restricted to participants (as of February 2005); related documents may be found at the International Broadcasters Convention (IBC) Web site. |
| External dependencies | The AAF SDK uses a Component Object Model (COM) interface and Structured Storage for the persistent object store. Although these are Microsoft technologies, the AAF SDK Web site states: "On non-Windows platforms COM support is provided by [the SDK's] own portable library." Thus it may be that the COM-support elements within SDK software itself is an external dependency; comments from specialists are welcome. |
| 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; one would expect users' overall systems to be secure. |
| Video elements | |
| Normal rendering for video | 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 (support for high image resolution) | Potentially excellent; depends upon the essence encodings selected. |
| Functionality beyond normal video rendering | Extensive in this authoring format, not documented here. |
| Sound elements | |
| Normal rendering for sound | 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 (support for high audio resolution) | Potentially excellent; depends upon encoding. |
| Support for multiple sound channels | There appears to be no limit to the number of tracks; thus multiple sound tracks may be included. |
| Functionality beyond sound normal rendering | Supports various features not documented here. |
| Tag type | Value | Note |
| Filename Extension | aaf | From The File Extension Source. |
| Internet Media Type | none found | Comments welcome |
| Magic numbers | none found | Comments welcome |
| File signature (512 byte sector) | {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 (4096 byte sector) | {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. |
| General | From the AAF Association Web site: "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. In the Gilmer's words, a protocol says, "use the AAF specifications 'this' way for 'this' application." |
| History | From the AAF Association Web site: "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." |
URLs
• Advanced Authoring Format (AAF) Object Specification v1.1, 2004-11-05 (http://www.aafassociation.org/html/specs/aafobjectspec-v1.1.pdf).
• Advanced Authoring Format (AAF) Low-Level Container Specification v1.0.1, 2004 (http://www.aafassociation.org/html/specs/aafcontainerspec-v1.0.1.pdf).
• Advanced Authoring Format (AAF) Stored Format Specification v1.0.1, 2004 (http://www.aafassociation.org/html/specs/aafstoredformatspec-v1.0.1.pdf).
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URLs
• AAF Association (http://www.aafassociation.org/).
• AAF mission statement (http://www.aafassociation.org/html/AAFMission.html).
• AAF and COM (Microsoft Component Object Model) (http://www.aafassociation.org/html/techinfo/COMaaf.html).
• AAF software developers kit (SDK) (http://aaf.sourceforge.net/).
• About XML for AAF and MXF at the International Broadcasters Convention (IBC) Web site (http://www.broadcastpapers.com/asset/IBCSonyXMLDictionary01.htm).
• The File Extension Source (http://filext.com/).
Print
• Motion Imaging, July/August 2004. This double issue of the monthly journal of the Society of Motion Picture, and Television Engineers (SMPTE) is devoted to the Advanced Authoring Format (AAF) and the Material Exchange Format (MXF).
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