From http://www.w3schools.com (Copyright Refsnes Data)
Video can be stored in many different formats.
The AVI (Audio Video Interleave) format was developed by Microsoft.
The AVI format is supported by all computers running Windows, and by all the most popular web browsers. It is a very common format on the Internet, but not always possible to play on non-Windows computers.
Videos stored in the AVI format have the extension .avi.
The Windows Media format is developed by Microsoft.
Windows Media is a common format on the Internet, but Windows Media movies cannot be played on non-Windows computer without an extra (free) component installed. Some later Windows Media movies cannot play at all on non-Windows computers because no player is available.
Videos stored in the Windows Media format have the extension .wmv.
The MPEG (Moving Pictures Expert Group) format is the most popular format on the Internet. It is cross-platform, and supported by all the most popular web browsers.
Videos stored in the MPEG format have the extension .mpg or .mpeg.
The QuickTime format is developed by Apple.
QuickTime is a common format on the Internet, but QuickTime movies cannot be played on a Windows computer without an extra (free) component installed.
Videos stored in the QuickTime format have the extension .mov.
The RealVideo format was developed for the Internet by Real Media.
The format allows streaming of video (on-line video, Internet TV) with low bandwidths. Because of the low bandwidth priority, quality is often reduced.
Videos stored in the RealVideo format have the extension .rm or .ram.
The Shockwave format was developed by Macromedia.
The Shockwave format requires an extra component to play. This component comes preinstalled with the latest versions of Netscape and Internet Explorer.
Videos stored in the Shockwave format have the extension .swf.
From http://www.w3schools.com (Copyright Refsnes Data)