If you watch videos online, you have most likely encountered the FLV format more than once. So what does that "FLV" file extension mean? FLV stands for "FLash Video", and it's typically used by various Flash-based video players on sites like YouTube, Google Video, Reuters.com and Yahoo! Video. and similar to deliver video over the Internet. Many television news operations are also using Flash Video on their websites.

FLV was initially a proprietary format. However, since version 9 of the player and up to the most recent public release the format has been open. Now FLV files can also contain H.264 video and HE-AAC audio streams. Though the file format itself is open now, the codecs still used with it are patented. This, however, hasn't prevented many freeware video players from adding FLV support, though it may not be immediately available in players bundled with the OS.

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 MPlayer, VLC media player (my favorite), Quicktime, or any player which uses DirectShow filters (such as Media Player Classic, Windows Media Player, and Windows Media Center) when the ffdshow filter is installed.

The quality of playback varies between players. Common issues include :

• Scaling problems. Any scaling may introduce lots of artifacts.
• Problems with seeking. For example, VLC player often terminates playback when you try to move to a different part of the video.
• Incompatibility with some players and/or mobile devices. This can be worked around by converting the FLV to other formats, e.g. AVI or MPEG. Luckily there are multiple freeware tools that can facilitate the conversion.

Overall, FLV is a very popular format for online video, and, quality issues aside, shows no signs of disappearing.