Xvid (formerly "XviD") is a video codec library following the MPEG-4 standard. Xvid features MPEG-4 Advanced Simple Profile features such as b-frames, global and quarter pixel motion compensation, lumi masking, trellis quantization, and H.263, MPEG and custom quantization matrices.

Xvid is a primary competitor of the DivX Pro Codec (Xvid being DivX spelled backwards). In contrast with the DivX codec, which is proprietary software developed by DivX, Inc., Xvid is free software distributed under the terms of the GNU General Public License.[1] This also means that unlike the DivX codec, which is only available for Microsoft Windows and Mac OS X[2] (although there is an x86 DivX codec download "for Linux developers", it is not officially available from the main DivX website and has not been updated since 2006[3]), Xvid can be used on all platforms and operating systems for which the source code can be compiled.