Flash Video (FLV) is a container file format used to deliver video over the Internet using Adobe Flash Player (initially produced by Macromedia) versions 6–10. Flash Video content may also be embedded within SWF files. There are two different video file formats defined by Adobe Systems and supported in Adobe Flash Player: FLV and F4V. The audio and video data within FLV files are encoded in the same way as they are within SWF files. The latter F4V file format is based on the ISO base media file format and is supported starting with Flash Player 9 update 3.
The format has quickly established itself as the format of choice for embedded video on the web. Notable users of the Flash Video format include YouTube, Google Video, Yahoo! Video, metacafe, Reuters.com, and many other news providers. The standards documentation for BBC Online deprecates the use of other formats previously in use on its sites such as RealVideo or WMV.
Though the Flash Video container format itself is open, the codecs used with it are patented. Flash Video FLV files usually contain material encoded with codecs following the Sorenson Spark or VP6 compression formats. The most recent public releases of Flash Player also support H.264 video and HE-AAC audio.
Flash Video is viewable on most operating systems, via the widely available Adobe Flash Player and web browser plugin, or one of several third-party programs.
Codec support
Supported media types in FLV file format:
* Video: Sorenson Spark (Sorenson H.263), H.264, VP6, Screen video
* Audio: ADPCM, MP3, Linear PCM, Nellymoser, AAC, Speex, G.711(reserved for internal use)
FLV Format Details
Commonly, Flash Video FLV files contain video bit streams which are a variant of the H.263 video standard, under the name of Sorenson Spark (FourCC FLV1). Sorenson Spark is an older codec for FLV files but it is also a widely available and compatible one. It is the required video compression format for Flash Player 6 or 7. Flash Player 8 and newer revisions also support the playback of On2 TrueMotion VP6 video bit streams (FourCC VP6F or FLV4). It is the preferred video compression format for use with Flash Player 8 and higher. On2 VP6 can provide a higher visual quality than Sorenson Spark, especially when using lower bit rates. On the other hand it is computationally more complex and therefore will not run as well on certain older system configurations.
Flash Player 9 Update 3, released on December 3, 2007, also includes support for the new Flash Video file format F4V and H.264 video standard (also known as MPEG-4 part 10, or AVC) which is even more computationally demanding, but offers significantly better quality/bitrate ratio. Specifically, Flash Player now supports video compressed in H.264 (MPEG-4 Part 10), audio compressed using AAC (MPEG-4 Part 3), the F4V, MP4 (MPEG-4 Part 14), M4V, M4A, 3GP and MOV multimedia container formats, 3GPP Timed Text specification (MPEG-4 Part 17) which is a standardized subtitle format and partial parsing support for the 'ilst' atom which is the ID3 equivalent iTunes uses to store metadata. MPEG-4 Part 2 video is not supported.
The Flash Video FLV file format supports two versions of a so called 'screenshare' (Screen video) codec which is an encoding format designed for screencasts. Both these formats are bitmap tile based, can be lossy by reducing color depths and are compressed using zlib. The second version is only playable in Flash Player 8 and newer.
Audio in Flash Video files is usually encoded as MP3. However, audio in Flash Video FLV files recorded from the user's microphone use the proprietary Nellymoser codec. FLV files also support uncompressed audio or ADPCM format audio. Recent versions of Flash Player 9 support AAC (HE-AAC/AAC SBR, AAC Main Profile, and AAC-LC).
Support for encoding Flash Video files is provided by an encoding tool included with Adobe's Flash Professional and Creative Suite products, On2's Flix encoding tools, Sorenson Squeeze, FFmpeg and other third party tools.
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