Open Source in MPEG

Covenor of MPEG, Dr. Chiariglione gives the history of the Moving Picture Experts Group and explains the characteristics of the MPEG open-source software process.
Why a Standard for MPEG-4?

Readers may wonder why, if the coding algorithm is implemented in software, there was a need to develop a standard. Shouldn't it suffice to download the code that allows for the decoding of the particular algorithm used to produce the bitstream of your interest?

In the early days of MPEG-4's development this question used to be asked very often, but today, with the ever-expanding use of MP3, it is easier to understand the benefits of having a standard: a playback device is not necessarily connected to the network. Instead, it may be on a broadcast channel, a stand-alone or portable device; the devices can use many different CPUs for which it could be too costly to develop playback codes; the hardware may use an ASIC for the audio-visual decoding that is not upgradeable; or it may have been designed to run with just the amount of RAM that the standard algorithm requires. In other words, it is simpler to have a common standard on which business opportunities can multiply, instead of having to struggle with incompatibilities all over the place.

Lastly, it should be kept in mind that compression coding is not a transparent operation. In general, the lower the bitrate used, the more the quality is affected negatively. Transcoding from one algorithm to another may simply produce garbage. Also, the idea that compression technology keeps improving is a myth. Only now, after many years, is MPEG re-issuing a call for proposals for video compression technologies because of the feeling that there may be something worth considering. For audio compression MPEG is still at the level of issuing a call for evidence because the group is not convinced this is an area currently worth pursuing.

The MPEG-4 “Open Source”

The very size of the standard has transformed the development of the reference software into a huge undertaking. It is therefore interesting to see how such a project was managed. These are the most important features:

  • The condition was set that any component of the standard, both normative (decoder) and informative (encoder), had to be implemented in software. For any proposal to be accepted and adopted, it was a condition that source code be made available and the copyright released to ISO.

  • For each portion of the standard, a manager of the code was appointed: a representative of Microsoft and MoMuSys for video in C++ and C respectively, Fraunhofer for natural audio, MIT for Structured Audio, ETRI for Text-to-Speech interface, Optibase for the so-called “Core” (the code portion on which all media decoders and other components plug in), Apple for the so-called MPEG-4 File Format, etc.

  • Each portion of the standard had a manager of experiments appointed. This manager integrated the code of the accepted tools in the existing code base.

  • Unlike traditional open-source software projects, only MPEG members could participate in the project. Discussions were usually held (and the practice still continues) on e-mail reflectors that are open to non-MPEG members.

MPEG is a place where new ideas are continuously forged. One idea was generated by the fact that while the reference code is intended to be “reference” (normative or informative as the case may be), it is not intended to be efficient. Therefore, since December 1999, MPEG has been working on a new part of MPEG-4 that will contain optimized code (e.g., optimized ways to search for motion vectors, a computationally expensive part of the standard). Any implementer can take this code and use it free of copyright. The condition has been set, however, that such optimized code should not require patents. A second idea, launched in October 2000, led to the decision to develop an MPEG-4 “reference hardware description”. It is expected that this will further promote the use of MPEG-4 as the basic multimedia infrastructure in both software and hardware.

The text of the so-called “copyright disclaimer” that is found on all MPEG-4 software modules is given below.

This software module was originally developed by <First Name 1> <Last Name 1> (<Company Name 1>) and edited by <First Name 2> <Last Name 2> (<Company Name 2>), <First Name 3> <Last Name 3> (<Company Name 3>), in the course of development of the <MPEG standard>. This software module is an implementation of a part of one or more <MPEG standard> tools as specified by the <MPEG standard>. ISO/IEC gives users of the <MPEG standard> free license to this software module or modifications thereof for use in hardware or software products claiming conformance to the <MPEG standard>. Those intending to use this software module in hardware or software products are advised that its use may infringe existing patents. The original developer of this software module and his/her company, the subsequent editors and their companies, and ISO/IEC have no liability for use of this software module or modifications thereof. Copyright is not released for non-<MPEG standard>-conforming products. <Company Name 1> retains full right to use the code for its own purpose, assign or donate the code to a third party and to inhibit third parties from using the code for non-<MPEG standard>-conforming products. This copyright notice must be included in all copies or derivative works. Copyright ( 199_).