FLV (Flash Video) "is a proprietary file format used to deliver video over the Internet using Adobe Flash Player (formerly known as Macromedia Flash Player) version 6, 7, 8, or 9. FLV content may also be embedded within SWF files. Notable users of the FLV format include YouTube, Google Video, Reuters.com, Yahoo! Video and MySpace.

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 such as Media Player Classic (with the ffdshow codecs installed), MPlayer, or VLC media player.

The Adobe Flash Player is a multimedia and application player created and distributed by Adobe. It plays SWF files which can be created by the Adobe Flash Authoring tool, Adobe Flex or a number of other Adobe and third party tools. It has support for a programming language called ActionScript, which can be used to display Flash Video from an SWF file. Because the Flash Player runs as a browser plug-in, it is possible to embed Flash Video in web pages and view the video within a web browser.

Commonly FLV files contain video bit streams which are a variant of the H.263 video standard, under the name of Sorenson Spark. Flash Player 8 and newer revisions support the playback of On2 TrueMotion VP6 video bit streams. 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.

An optional alpha channel which represents per pixel transparency is supported by including a second simultaneous video stream