What is FLV?

The FLV/F4V open specification documents the file formats for storing media content used to deliver streaming audio and video for playback in Adobe® Flash® Player and Adobe AIR™ software. FLV and F4V are the de facto standard for web video today; 80% of online videos are viewed worldwide using Adobe Flash® technology.

An FLV file encodes synchronized audio and video streams. The audio and video data within FLV files are encoded in the same way as audio and video within SWF files. Starting with SWF files published for Flash Player 6, Flash Player can exchange audio, video, and data over RTMP connections with Adobe Flash® Media Server. One way to feed data to Flash Media Server (and thus to Flash Player clients) is from files in the FLV file format. Starting with SWF files published for Flash Player 7, Flash Player can also play FLV files directly with MIME type video/x-flv. An FLV file encodes synchronized audio and video streams.

The F4V format is based on the format specified by ISO/IEC 14496-12: ISO base media file format. Starting with SWF files published for Flash Player 9 Update 3 (9,0,115,0), Flash Player has been able to play F4V files.

More details, please visit: http://www.adobe.com/devnet/flv/