.FLV (Flash Video Format)
Flash video (FLV) is the single most common sharing format on the web today. You’ll see the .FLV file extension on videos encoded by Adobe Flash software to play within the Adobe Flash Player. Virtually everyone (99%) has the adobe player installed in their browser and so this has fast become the most common online video viewing platform. Almost all the video sharing sites stream video in flash. You can upload formats other than flash, and those sites will convert it into flash for streaming to the end user. Notable users of the Flash Video format include YouTube, Yahoo! Video, MySpace, and many others.
Many television news operations are also now using Flash Video on their websites as a way to keep viewers up to date at all times. Most of those sites accept uploads in a handful of formats like QuickTime, mpeg4, or wmv, and then they convert it to flash or MP4 before actually putting it out on the net for viewing.
In addition to the nearly universal flash video player, FLV is popular because it gives one of the smallest file sizes after compression yet it retains fairly good quality. This means that the videos load quickly on the internet, and won’t spend a lot of time using up your bandwidth. If you self-host your own videos, you should convert them to flash for greatest compatibility with the highest percentage of Internet viewers.
Although FLV’s are the most common format found on the web today, the standard is moving towards the use of using MP4 H.264 files within flash players as it is compatible with both online and mobile (iPhone), not to mention some HTML5 browser support (Safari, Chrome).