divx

DivX is a video codec created by DivX, Inc. (formerly DivXNetworks, Inc.), which has become popular due to its ability to compress lengthy video segments into small sizes while maintaining relatively high visual quality. DivX uses lossy MPEG-4 Part 2 compression, where quality is balanced against file size for utility. It is one of several codecs commonly associated with ripping, where audio and video multimedia are transferred to a hard disk and transcoded. As a result, DivX has been a center of controversy because of its use in the replication and distribution of copyrighted DVDs.

Many newer "DivX Certified" DVD players are able to play DivX encoded movies. However, "DivX" should not be confused with "DIVX", an unrelated attempt at a new DVD rental system employed by the US retailer Circuit City. The winking emoticon in the early "DivX ;-)" codec name was a tongue-in-cheek reference to the failed DIVX system.

History

DivX ;-) 3.22 and earlier versions generally refer to a hacked version of the Microsoft MPEG-4 Version 3 video codec, extracted around 1998 by French hacker Jerome Rota (also known as Gej). The Microsoft codec, which originally required that the compressed output be put in an ASF file, was altered to allow other containers such as AVI. From 1998 through 2002, independent enthusiasts within the DVD-ripping community created software tools which dramatically enhanced the quality of video files that the DivX ;-) 3.11 Alpha codec could produce. One notable tool is Nandub, a modification of the open-source VirtualDub, which features two-pass encoding (termed "Smart Bitrate Control" or SBC) as well as access to internal codec features.

In early 2000, Rota created a company (originally called DivXNetworks, Inc., renamed to DivX, Inc. in 2005) to improve DivX and steward its development. This effort resulted first in the release of the "OpenDivX" codec and source code on January 15, 2001. OpenDivX was hosted as an open source project on the Project Mayo web site (projectmayo.com). The company's internal developers and some external developers worked jointly on OpenDivX for the next several months, but the project eventually stagnated. In early 2001, DivX employee "Sparky" wrote a new and improved version of the codec's encoding algorithm known as "encore2." This code was included in the OpenDivX public source repository for a brief time, but then was abruptly removed. The explanation from DivX at the time was that "the community really wants a Winamp, not a Linux." It was at this point that the project forked. DivX took the encore2 code and developed it into DivX 4.0, initially released in July 2001. Other developers who had participated in OpenDivX took encore2 and started a new project—XviD—that started with the same encoding core. The company released a clean room version of the codec as DivX 4.0 in July 2001. DivX, Inc has since continued to develop the DivX codec, releasing DivX 5.0 in March 2002.

The latest generation, DivX 6, was released on June 15, 2005 and expands the scope of DivX from being just a codec to including a full media container format. DivX 6 introduces a new file format called "DivX Media Format" (with a .divx extension) that includes support for the following DVD-like features:

• Interactive video menus
• Multiple subtitles
• Multiple audio tracks
• Chapter points
• Other metadata
• Multiple format

While in previous generations video encoded with DivX was analogous to video formats such as MPEG-2, in its 6.0 generation the new DivX Media Format is analogous to media container formats such as Apple's QuickTime. In much the same way that media formats such as DVD specify MPEG-2 video as a part of their specification, the DivX Media Format specifies MPEG-4-compatible video as a part of its specification. However, despite the use of the ".divx" extension, this format is simply the AVI file format by another name. The methods of including multiple audio and even subtitle tracks involve storing the data in RIFF headers and other such AVI hacks which have been known for quite a while, such that even VirtualDubMod supports them. Of course, the traditional method of creating standard AVI files is still supported.

DivX and Spyware

At one point, DivX Networks offered for download an "ad supported" version of their DivX Professional product free of charge to users who were willing to view advertisements. The ads in question were delivered by the notorious Gator adware software. While this attracted much criticism at the time, it should be noted that users had to manually select the "ad supported" download rather than the for-pay professional version or the free version. Additionally, users were informed during installation of the ad-supported version that the Gator software would be installed on their PC and were presented with a license agreement to which they had to consent in order to continue the installation. Unfortunately, the Gator software would still install parts of itself without the user agreeing to this installation, and was notoriously difficult to remove after installation; this raised considerable consternation amongst DivX users, causing many to turn to its Open Source rival, XviD. The latter is freely available without installing adware and has been demonstrated in independent comparisons to produce better quality output (see section on Quality below).

Due to the generally hostile opinion towards spyware on the Internet, DivX Networks announced on the DivX.com web site that, from July 15, 2004, no further DivX software would incorporate any adware [1]. Free versions of DivX Pro before 5.2 typically contained spyware. From 5.2 onwards, including version 6, no spyware was included. When accessed in March 2006, the Professional version of DivX was only available in the form of a paid release or a 6-month free trial with no adware included.

Current Version

The current version of the DivX Community Codec, which is the same for all platforms, is version 6.3, available from DivX.com. The latest version of the DivX package for Windows 2000/XP (which contains DivX Player 6.3.2, DivX Community Codec 6.2.5, and DivX Web Player 1.0) is version 6.3, and the latest version of the DivX package for Mac OS X (which contains DivX Player 1.0.3, DivX Community Codec 6.2.5, and DivX Web Player 1.0.2) is version 6.5, released May 25, 2006. In addition, an unofficial DivX for Linux codec update has also been released at version 6.1.1. The DivX codec and DivX Player are available for free at the DivX website. Paying customers can access additional features of the DivX codec in the registered version, known as DivX Pro, and can also use DivX Converter, a one-click encoding application as a revamp of Dr. DivX and associated encoding tools (such as the Electrokompressiongraph™, or EKG, which helped increase the viewability of highly compressed high-motion scenes). The latest version of DivX Converter for Windows is 6.2, and the latest version of DivX Converter for Mac is 1.1.1.

Recently DivX have also released the DivX Web Player 1.0.1 (formerly known as the DivX Browser Plug-In Beta) via the DivX Labs website, demonstrating 720p HD playback live inside major browsers for Windows and Mac OS. Dr DivX 2 OSS, an Open Source DivX transcoding application, is available from SourceForge.

An open source version of the codec—called OpenDivX®—was released by DivX in early 2001, and this version served as the basis for the open source XviD codec, the source code of which is maintained by an independent group.

The main competitors in the for-license video compression software market are Adobe's Flash 8 (using ON2's VP6),Microsoft's Windows Media Video series, Apple Computer's QuickTime, and the RealNetworks RealVideo series.

Quality, alternative MPEG-4 ASP implementations

While DivX has long been renowned for its excellent video quality, its open-source equivalent XviD, also based on MPEG-4 Part 2, now offers comparable quality. In a series of subjective quality tests at Doom9.org, the DivX codec was beaten by XviD in the 2003, 2004, and 2005 tests.

The open source library libavcodec can decode MPEG-4 video encoded with DivX (and other MPEG-4 codecs, such as XviD or libavcodec MPEG-4). Combined with image postprocessing code from the MPlayer project, it has been packaged into a DirectShow decoding filter called ffdshow, which can be used with most Windows video players and reportedly achieves higher image quality while generating less CPU load than the DivX codec^[1].

Since the standardization of H.264/MPEG-4 AVC, also known as MPEG-4 Part 10, a new generation of codecs has arisen, such as x264. Despite being at a relatively early stage of development, these codecs already out-performed DivX in Doom9's 2005 quality test, thanks to the more advanced features of MPEG-4 Part 10. Part 10's advanced features come at a cost: they are two to three times more CPU intensive than the relatively lightweight algorithms used in the DivX codec. It remains to be seen whether DivX will release a new codec based on the newer specification, like the XviD team have with their XviD AVC codec.

References

1. ^ ffdshow review from afterdawn.com, accessed 17 August 2006

See also

• List of multimedia codecs
• Comparison of container formats
• Xvid

External links

• DivX.com The official DivX website
• DivX Labs Community DivX website, with betas and ongoing projects
• DivX resources at the Open Directory Project