Sustainability of Digital Formats: Planning for Library of Congress Collections |
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Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact |
Full name | Macromedia Flash FLV Video File Format |
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Description |
Binary file format that delivers "bitmapped" video, limited to one video and one audio stream per file, over the Internet to one or another versions of the Macromedia Flash Player. FLV content may also be incorporated in SWF files by ActionScript external references. Temporary note (March 2010): Version 8 appears to have been current when this description was drafted in 2007. Although Adobe Systems Inc. had acquired Macromedia in 2005, the specification for version 8 of the SWF file format (SWF_8), together with documentation of the FLV format, was published that year under the Macromedia brand. The October 2005 issue of Macworld magazine reports that the Flash Professional 8 application offers a new video codec called VP6 from a company named On2 which was later acquired by Google. Specifications for later versions of the Flash file format have been published by Adobe, including version 10 (dated 2008), still available in 2010 from http://www.adobe.com/devnet/swf/. The compilers of this resource hope to update this Website soon to add descriptions of newer versions. |
Production phase | Used for final-state, end-user delivery. |
Relationship to other formats | |
May contain | Sorenson encoded video. 1 |
May contain | Screen video bitstream format and Screen Video Version 2, not documented here. |
May contain | On2 Truemotion VP6 bitstream format, not documented here. |
May contain | Raw PCM sampled audio content, not documented here. |
May contain | ADPCM, Adaptive Delta Pulse Code Modulation. For audio content |
May contain | MP3_ENC, MP3 |
May contain | Nellymoser Asao (speech compression) audio content, not documented here. |
Other | SWF_7, Macromedia Flash SWF File Format, Version 7. Explanatory note: FLV content may be associated with SWF by means of ActionScript external references. |
Other | SWF_8, Macromedia Flash SWF File Format, Version 8. Explanatory note: FLV content may be associated with SWF by means of ActionScript external references. |
LC experience or existing holdings | None |
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LC preference | For file-based, lossy compressed video, the Library prefers members of the MPEG-2 or MPEG-4_FF_2 family. |
Disclosure | Fully documented. Developed by Macromedia, Inc., now owned by Adobe Systems. |
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Documentation | Provided within The Macromedia Flash (SWF) and Flash Video (FLV) File Format Specification, Version 8, n.d.(copyright notice 2005), pp. 257-65. In 2007, this specification was available from an Adobe Web page (http://www.adobe.com/licensing/developer/) but the compiler of this resource could not find an online copy in 2010. As of late 2013, the specification for version 10.1 is available |
Adoption | Not investigated. |
Licensing and patents | In 2007, information was provided at an Adobe licensing page (http://www.adobe.com/licensing/developer/). In 2010, licensing information about Adobe products (not content or file/wrapper formats) was provided at Adobe product license agreements. |
Transparency | Transparent wrapper; proprietary binary content within. |
Self-documentation | Various headers provide technical information; the specification does not indicate a location to embed descriptive metadata. |
External dependencies | None. |
Technical protection considerations | None known to the compilers of this document. |
Moving Image | |
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Normal rendering | Good support |
Clarity (high image resolution) | "Bitmapped" video in FLV files may be compressed in various ways (see relationships above); the video quality in these encodings is expected to range from good to very good. |
Functionality beyond normal rendering | Certain capabilities may relate to the use of ActionScripts. |
Sound | |
Normal rendering | Good support |
Fidelity (high audio resolution) | The specification limits uncompressed audio to 44 kHz sampling and 16 bit words, thus providing very good fidelity. The use of compressed audio formats (see relationships above) will reduce fidelity in accord with the specific encoding and settings selected. |
Multiple channels | Stereo only. |
Support for user-defined sounds, samples, and patches | None. |
Functionality beyond normal rendering | Certain capabilities may relate to the use of ActionScripts. |
Tag | Value | Note |
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Filename extension | flv |
From The File Extension Source. The Wikipedia article on Adobe Flash (consulted February 2007) includes a list of file types (with extensions) associated with the Flash family. |
Internet Media Type | video/x-flv |
From the specification, p. 257 |
Magic numbers | Hex: 46 4C 56 ASCII: FLV |
From the specification, p. 258. The next byte in the file provides the version number; Hex 01 (0x01) for FLV version 1 (this example is the only FLV version number provided in the 2005 specification) |
General | |
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History |
1 Flash documentation does not state a number for "their" version of Sorenson but describes the codec as a variant of ITU-T (International Telecommunications Union-Telecommunication Standardization Sector) recommendation H.263 (MPEG-4_V). In early 2006, one of Sorenson's compression applications to produce content for Flash offered the Sorenson_3 codec, described by experts as a variant of ITU-T H.264 (MPEG-4_AVC). By late 2006, Sorenson offered new compression applications with other outputs.
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