(Copyright © 2013 Xvid Solutions GmbH – www.xvid.org)
Xvid is a video codec for PC, whereas codec is an abbreviation for [co]der/[dec]oder, hence describes a program to encode and decode digital video. The purpose of encoding video data is to reduce redundancies – that means to make it smaller for faster transmission over computer networks or for more efficient storage on computer disks.
Hence, Xvid can somewhat be seen as a ZIP for video. But unlike ZIP, Xvid is not lossless. That means that a video after compression and decompression with Xvid won't be identical to the original source. Typically however, a difference to the source is visually imperceptible.
So Xvid removes information that is not important for human perception, which is somewhat similar to MP3 for audio. This enables very high compression rates that allow to effectively work with digital video on home computers at all. To give an example: uncompressed digital video is huge and requires about 100 GB per hour at PAL resolution. The same video would require just 500 MB per hour at very high quality when compressed with Xvid. That is a compression ratio of 200:1.
Xvid is Free Software and released under the GNU GPL license. This means that the source code of the software is publically available and programmers are allowed to make modifications to the code. Also, redistribution of Xvid is permitted but only under the terms of the GPL license.
So the GPL grants recipients more freedoms than it’s common with other software. Therefore, and due to its very high image quality that has been approved in independent tests conducted by third parties the Xvid codec has gained great popularity in the recent past and has become the codec of choice when it comes to exchanging digital video.