FLV (Flash Video) is a container file format used to deliver video over the Internet using Adobe Flash Player version 6 and newer. Flash Video content may also be embedded within SWF (an Adobe Flash file format used for multimedia, vector graphics and ActionScript files). There are two different video file formats known as Flash Video, .flv and .f4v. The audio and video data and metadata (such as subtitles and closed captioning) within FLV files are encoded in the same manner as they are within SWF files, making. The F4V file format is based on the ISO base media file format. Both formats were developed by Adobe Systems. FLV was originally developed by Macromedia.

Flash Video is the standard for web-based streaming video over RTMP (Real Time Messaging Protocol). Notable users include YouTube, Hulu, VEVO, Yahoo! Video, metacafe, Reuters.com, and many other news providers. The FLV and F4V formats make possible convenient file-sharing for uses such as reference, archiving filmed material, editing and transcription.

Flash Video FLV 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 HE-AAC audio. All of these compression formats are restricted by patents.

Flash Video is viewable on most operating systems via the Adobe Flash Player and web browser plugin or one of several third-party programs. Apple’s iOS devices do not support the Flash Player plugin and so require other delivery methods such as provided by the Adobe Flash Media Server.

Commonly, 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 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, TrueMotion VP6 video bit streams (FourCC VP6F or FLV4). On2 VP6 can provide a higher visual quality than Sorenson Spark, especially when using lower bit rates. However, it is computationally more complex and therefore will not run as well on certain older system configurations.

Desktop-based applications that support Flash Video for Microsoft Windows, Mac OS X and Unix-based systems include Adobe Media Player, Media Player Classic, Mplayer, RealPlayer, VLC media player and Winamp. Mac OS devices can play flash videos in QuickTime with the help of additional software. PDA and smartphone-based applications that support Flash Video include Windows Mobile and Palm OS using the Core Pocket Media Player.