Information about Xvid

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, 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], Xvid can be used on all platforms and operating systems the source code can be compiled to.

History

In January 2001, DivXNetworks founded OpenDivX as part of Project Mayo which was intended to be a home for open source multimedia projects. OpenDivX was an open-source MPEG-4 video codec based on a stripped down version of the MoMuSys reference MPEG-4 encoder. The source code, however, was placed under a restrictive license and only members of the DivX Advanced Research Centre (DARC) had write access to the project CVS. In early 2001, DARC member Sparky wrote an improved version of the encoding core called encore2. This was updated several times before, in April, it was removed from CVS without warning. The explanation given by Sparky was "We (our bosses) decided that we are not ready to have it in public yet."^[3]

In July 2001, developers started complaining about a lack of activity in the project; the last CVS commit was several months before, bugfixes were being ignored, and promised documentation had not been written. Soon after, DARC released a beta version of their closed-source commercial DivX 4 codec, which was based on encore2, saying that "what the community really wants is a Winamp, not a Linux."^[4] Many accused DivXNetworks of starting OpenDivX for the sole purpose of harvesting other people's ideas to use in their DivX 4 codec, some were disappointed that the codec had stagnated and wanted to continue working on it, while others were angry at the way DivXNetworks handled a so-called open source project. It was after this that 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.

Patent issues

Some features of Xvid are believed to be covered by software patents in a number of countries (notably United States and Japan). For this reason, Xvid 0.9.x versions were not licensed in countries where these types of patents are enforceable. With the 1.0.x releases, a GNU GPL v2 license is used with no explicit geographical restriction. However, the legal usage of Xvid may still be restricted by local laws.^[5]

Sigma Designs controversy

In July 2002, Sigma Designs released an MPEG-4 video codec called the REALmagic MPEG-4 Video Codec. Before long, people testing this new codec found that it contained considerable portions of Xvid code. Sigma Designs was contacted and confirmed that a programmer had based REALmagic on Xvid, but assured that all GPL code would be replaced to avoid copyright infringement. When Sigma Designs released the supposedly rewritten REALmagic codec, the Xvid developers immediately disassembled it and concluded that it still contained Xvid code, only rearranged in an attempt to disguise its presence. The Xvid developers decided to stop work and go public to force Sigma Designs to respect the terms of the GPL. After articles were published in Slashdot^[6] and The Inquirer,^[7] in August 2002 Sigma Designs agreed to publish their source code.^[8]

Playing Xvid encoded files

Due primarily to concerns over patents, the official Xvid homepage does not provide binary versions of the Xvid codec. Video for Windows codecs (and DirectShow decoding-only filters) for Microsoft Windows are, however, made available at supporting websites. For Linux users, many distributions provide an Xvid codec for use with media players such as MPlayer and VLC. However, all these players use the FFmpeg MPEG-4 decoder by default and therefore don't require (or don't support) decoding with the Xvid codec.

Xvid is not a video format. Since Xvid uses MPEG-4 Advanced Simple Profile (ASP) compression, video encoded with it is MPEG-4 ASP video (not "Xvid video") and can therefore be decoded with all MPEG-4 ASP compliant decoders. This includes a large number of media players, in particular all the ones based on the free/open source libavcodec library.

Xvid encoded files can be written to a CD or DVD and played in a DivX compatible DVD player. However, Xvid can optionally encode video with advanced features that most DivX set-top players do not support. Files encoded with global motion compensation, Qpel, MPEG quantization, multiple B-frames or files that exceed the VBV limitations may not playback properly on DivX Certified hardware devices.

For example, Xvid specifies three warp points for its implementation of global motion compensation as opposed to the single warp point implementation of DivX. Enabling some of the more advanced encoding features can compromise player compatibility. Some issues exist with the custom quantization matrices used in tools such as AutoGK that automate encoding with Xvid. This can (depending on the decoder chipset of the set-top player in question) produce videos that have unstable playback and artifacts. However, most recent model DivX compatible DVD players have improved support for custom quantization matrices.

A QuickTime Xvid component is available for Mac OS X.^[9]

See also:

Encoding applications

On Microsoft Windows, Xvid can be used for encoding in all applications that support encoding through the VfW framework. This includes popular applications such as VirtualDub and DVDx.

Platform and framework independent applications such as MEncoder or Avidemux access the Xvid library directly and can be used for encoding with Xvid on numerous operating systems including Windows, Linux, BSD and Mac OS X.

References

See also

• Xvid Qf
• List of codecs
• Comparison of video codecs

External links

• Xvid.org web site
• XviD Setup/Reference Guide @ Digital Digest
• Binary builds for Windows

•  • [ e] Data compression software implementations
Video codecs (Comparison)	MPEG-4 ASP 3ivx DivX Nero Digital FFmpeg MPEG-4 HDX4 Xvid H.264/MPEG-4 AVC CoreAVC Nero Digital AVC QuickTime H.264 x264 Lossless CorePNG FFV1 Huffyuv Lagarith MSU Lossless Others Cinepak Sorenson Dirac Indeo VP3 VP7 Pixlet Snow Tarkin Theora WMV SIF1
Audio codecs (Comparison)	General ADPCM ATRAC Dolby Digital Musepack TwinVQ Vorbis WMA Speech/Voice iLBC IMBE iSAC QCELP Speex Truespeech Lossless Apple Lossless Dolby TrueHD FLAC Monkey's Audio OptimFROG TTA WavPack WMA Lossless
Archivers (Comparison)	Open Source 7-Zip Ark File Roller KGB Archiver PeaZip The Unarchiver Freeware DGCA Filzip GCA IZArc StuffIt Expander TUGZip Zipeg ZipGenius WinUHA Proprietary ALZip BOMArchiveHelper MacBinary PowerArchiver Squeez StuffIt WinAce WinRAR WinRK WinZip Command line ARC ARJ JAR bzip2 compress gzip Info-ZIP LHA lzop NABOB PAQ PKZIP RAR SBC UPX
See for methods and for formats