Source is http://best-damn-codec.blogspot.com/...t-is-xvid.html
XviD is not a file format, it's an open-source codec that based on MPEG-4 standard, specifically MPEG-4 Part 2 Advanced Simple Profile (ASP). XviD is the wolrd's first open-source video codec distributed under the terms of GNU General Public License. Its good quality and efficiency has made it the most popular video codec all over the world.

XviD was initially developed by a fork of OpenDivX, which was an open-source MPEG-4 video codec. Now it's developed by volunteer programmers from all over the world. The latest version of XviD is Xvid 1.3.2 released on Tuesday 31. of May 2011. You can get it from XviD official website: http://www.xvid.org/Home-of-the-Xvid-Codec.1.0.html.

In recent years, XviD is always the most popular codec in the world. About 90% of movies and TV series on BitTorrent and eMule use XviD as their codec. XviD is a major competitor of the DivX Pro, which is not open-source and only available for a limited number of platforms, while XviD can be used on all platforms.

Video compressed with XviD doesn't have a fixed file extension, it can be .avi, .mkv, .mp4, etc. We can't tell the codec of a video only from its file extension. For example, the video codec of an AVI file can be DV codec, XviD or others; and its audio codec can be PCM, AC3 or MP3.

You must have founded that XviD is just a reverted order word of DivX. So you might wonder what's the relation between them and their differences. With these questions, let's review the history of XviD.

History

In January 2001, DivXNetworks (DXN) founded OpenDivX as part of Project Mayo which was intended to be a home for open source multimedia projects. Many computer geeks joined the project and they quickly developed the OpenDivX codec, and more powerful codec Encore2 later. However, DXN made Encore2 private in July 2001 - DXN removed Encore2 from public, built a company called DivX Networks Inc. and a website and released DixX 4, which is based on Encore2. As a result of this, Project Mayo suspended. After this, a fork of OpenDivX was created, using the latest version of encore2 that was downloaded before it was removed. Since then, all the OpenDivX code has been replaced and Xvid has been published under the GNU General Public License.

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