Tuesday, December 9, 2008

Difference between DivX and Xvid?

First, an example, what do these things have in common?
  1. Microsoft in Redmond, WA
  2. Apple in Cupertino, CA
  3. LAME, the open source project on SourceForge
Answer: all of them offer a MP3 audio encoder.

  1. DivX Inc. in San Diego, CA
  2. Xvid Solutions in Hof, Germany
  3. XviD, the open source project on SourceForge
All of them offer an MPEG4 Advanced Simple Profile (ASP) video encoder. The Xvid Solutions encoder is the same as the XviD open-source encoder and often appears in free software. The DivX encoder is proprietary and only appears in DivX Certified software such as the free DivX Converter.

What's missing in this comparison with MP3 is a colloquial name for a video file. Some people call them MPEG4 files but that's not descriptive enough. MPEG4 ASP is a broad standard that includes many esoteric features that are not in common use. Even devices which claim to play "MPEG4 ASP" files probably do not actually support all MPEG4 ASP features.

Some people talk of "DivX" files or "Xvid" files. Usually they mean "MPEG4 ASP files created by the DivX (or Xvid) encoder". However, there are many software programs that use neither the DivX encoder or the Xvid encoder yet still claim to create "DivX" files and/or "Xvid" files.

DivX Inc. and Xvid Solutions offer a certification program for consumer electronics to guarantee compatibility among devices by precisely defining a DivX file and an Xvid file. However, there are many devices which claim "DivX" and/or "Xvid" playback even though the device is not certified by either company.

It's no surprise then that consumers are often confused. Terms appear thrown together and comparisons are made in non-sensible ways.

In fact, since DivX and Xvid are two different encoders that both produce MPEG4 ASP video in an AVI file container, you can't tell the difference between a DivX encoded video and an Xvid encoded video if you were just looking at the video data in the file. However, the encoders leave tell-tale indicators embedded in the file that usually clearly indicate which encoder was used.

It might seem then, that it doesn't matter which encoder is used. That is true, however, DivX Inc. and Xvid.org have defined slightly different "profiles" for encoding. For example, the DivX Home Theater profile does not allow multiple warp point Global Motion Compensation or Quarter Pixel Estimation even though these features are allowed under the MPEG4 ASP standard and part of the Xvid "home" profile. The DivX encoder can make use GMC and QPel but by default, it does not.

For most people, the best advice is to only buy DivX Home Theater certified products and only use DivX Home Theater certified software. That way, video compatibility is guaranteed. Furthermore, DivX Home Theater files may contain features such as sub-titles or multiple audio tracks. These features are only supported by DivX Certified players. Non-certified devices that claim "DivX" compatibility will not do anything other than basic video playback. Non-certified encoders that claim to create "DivX" files cannot create DivX sub-titles or multiple audio tracks. For example, if you are careful with how you configure the Xvid encoder, you can create videos that play on most DivX devices but you'd be limited to making basic video files without advanced features.

Over 250 Million DivX Certified devices have been sold. Xvid Solutions offers a similar certification program but there are very few Xvid certified devices despite numerous claims of "Xvid" compatibility. Manufacturers get away with these claims because in practice nearly all "Xvid" files are actually videos created to the DivX standard using Xvid software. Few people actually make videos to any Xvid profile because they would be incompatible with the millions of DivX players. Whether they are using DivX software or Xvid software, people are almost always making DivX videos.

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