In a nutshell, AVI is one of the most popular video file formats. But there’s more to it than might seem at the first look – AVI (or Audio Video Interleave),is actually a multimedia “container format”. AVI files can contain both audio and video data (multiple tracks supported) in a file container that allows synchronous audio-with-video playback. The audio/video can be encoded with a various diverse codecs and quality.
The AVI format was introduced by Microsoft in November 1992 as part of its Video for Windows technology. Most AVI files also use the file format extensions developed by the Matrox OpenDML group in February 1996. These files are supported by Microsoft, and are unofficially called “AVI 2.0”.
While the AVI format is very popular, it’s not the best format for large videos. When AVI is used to store video in popular MPEG-4 codecs (e.g. Xvid and DivX) the files turn out bloated and larger than necessary. Other container formats, like Ogg and MP4, are more efficient.
So what does the “FLV” extension mean? FLV stands for “FLash Video”.
According to Wikipedia, Flash Video is a file format used to deliver video over the Internet using the Flash Player versions 6–10. Until version 9 of the player FLV was a proprietary format. However, the most recent public release of Flash Player also supports H.264 video and HE-AAC audio in the FLV file.
FLVs can also be embedded within SWF files.
You’ve probably seen the videos on YouTube – well, that’s Flash Video. Other sites that use this format include Google Video, Reuters.com and Yahoo! Video. Many television news operations are also using Flash Video on their websites.
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 (meh), 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.
Though the file format itself is open now, the codecs still used with it are patented.