Flash Video (FLV, F4V) is a container file format used to deliver video over the Internet using Adobe Flash Player versions 6-10. Flash Video content may also be embedded within SWF files. There are two different video file formats known as Flash Video: 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. Both formats are supported in Adobe Flash Player and currently developed by Adobe Systems. FLV was originally developed by Macromedia.

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, Hulu, Google Video, Yahoo Video, Metacafe, Reuters, and many other news providers.

Flash Video (FLV and F4V) files usually contain material encoded with codecs following the Sorenson Spark or VP6 video compression formats. The most recent public releases of Flash Player also support H.264 video and 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.

Flash Video FLV files contain video bit streams which are a proprietary variant of the H.263 video standard, under the name of Sorenson Spark. Sorenson Spark is an older codec for FLV files but it is also a widely available and compatible one, because it was the first video codec supported in Flash Player. It is the required video compression format for Flash Player 6 and 7.

Flash Player 8 and newer revisions also support the playback of On2 True-Motion VP6 video bit streams. On2 VP6 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.

And audio in Flash Video files is usually encoded as MP3. However, audio in Flash Video FLV files recorded from the user's microphone. Flash Player 10 released in 2008 also supports the open sourceSpeex codec. FLV files also support uncompressed ADPCM format audio. Recent versions of Flash Player 9 support AACaudio format.

Supported media types in FLV file format:

Video: On2 VP6, Sorenson Spark (Sorenson H.263), Screen video, H.264
Audio: MP3, ADPCM, Linear PCM, Nellymoser, Speex, AAC, G.711 (reserved for internal use)

Supported media types in F4V file format:

Video: H.264
Images (still frame of video data): GIF, PNG, JPEG
Audio: AAC, HE-AAC, MP3

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