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Macromedia Flash FLV Video File Format

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Macromedia Flash FLV Video File Format
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.

Local use Explanation of format description terms

LC experience or existing holdings None
LC preference For file-based, lossy compressed video, the Library prefers members of the MPEG-2 or MPEG-4_FF_2 family.

Sustainability factors Explanation of format description terms

Disclosure Fully documented. Developed by Macromedia, Inc., now owned by Adobe Systems.
    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.

Quality and functionality factors Explanation of format description terms

Moving Image
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.

File type signifiers Explanation of format description terms

Tag Value Note
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)

Notes Explanation of format description terms

General  
History  

Format specifications Explanation of format description terms


Useful references

URLs

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.


Last Updated: 12/11/2013