The Moving Picture Experts Group

MPEG Basics

 

The Moving Picture Coding Experts Group (MPEG) was established in January 1988 with the mandate to develop standards for coded representation of moving pictures, audio and their combination. It operates in the framework of the Joint ISO/IEC Technical Committee (JTC 1) on Information Technology and is formally Working Group 11 (WG11) of Subcommittee 29 (SC29) of the Joint  Technical Committee (JTC 1) of ISO/IEC.

Starting from its first meeting in May 1988 when 25 experts participated, MPEG has grown to an unusually large ISO Working Group. Usually some 350 experts from some 200 companies and organisations from > 20 countries take part in MPEG meetings. As a rule, MPEG meets four times a year (in January, April, July and October).

MPEG membership is based on individuals technical experts, typically belonging to companies and organisations. The MPEG environment is rather informal, even though it should not be forgotten that standards can be of high strategic relevance. Therefore it should be no surprise that operation of ISO standards committees is carefully regulated by "Directives" issued by ISO/IEC.

Unlike other standards committees where the development work is done outside and the role of the committee is by and large the management of the formal process of standards approval, the development of MPEG standards actually takes place in the Working Group. At each meeting different technical submissions are reviewed by the committee and work is assigned to members for the next meeting. This allows MPEG to attract the best expertise in its fields and to produce the technically most advanced standards. As a result of this working method MPEG manages hundrrds of documents every meeting.

These documents are restricted to MPEG members. From time to time, however, MPEG decides to post some of its output documents on the MPEG web site. These are typically calls for proposals, general descriptions of standards, approved or under development, the text of standards under ballot etc. As a rule standards in final form are NOT posted. However, it is possible to purchase them from sales@iso.org.

The ISO standards produced by MPEG are indicated by 5 digits (e.g. he ISO number for MPEG-1 is 11172 and for MPEG-2 is 13818). Published standards are the last stage of a long process that starts with the proposal of new work within a committee. These proposals of work (NP = New Proposal) are approved at Subcommittee and then at Technical Committee level (SC29 and JTC1 respectively, in the case of MPEG).

When the scope of new work has been sufficiently clarified, MPEG usually publishes requests for proposals, called Calls for Proposals CfP). Stay tuned to this MPEG Hot news page for further CfP.

Depending on the nature of the standard, documents of different nature may be produced. For Audio and Video coding standards the first document that is produced is called a Test Model (or similar name). The Test Model describes, in a programming language, the operation of the encoder and the decoder. The Test Model is used to carry out simulations to optimise the performance of the coding scheme. When MPEG has reached sufficient confidence in the stability of the standard under development, a Working Draft (WD) is produced. This is already in the form of a standard but is kept internal to MPEG for revision. When the WD has become sufficiently solid it becomes Committee Draft (CD). It is then sent to National Bodies (NB) for ballot. If the number of positive votes is above the quorum, the CD becomes Final Committee Draft (FCD) and is again submitted to NBs for the second ballot after a thorough review that may take into account the comments issued by NBs. If the number of positive votes is above the quorum the FCD becomes Final Draft International Standard (FDIS). ISO will then hold a yes/no ballot with National Bodies where no technical changes are allowed. The document then becomes International Standard (IS).

A WD usually undergoes several revisions before moving to CD stage. A key role is played by "Core Experiments", a tool to achieve collaboration between parties by letting well identified groups made of at least two different partners, study different technical options. Each revision involves a large number of experts who draw the committee's attention to possible errors contained in the document. Moreover, depending on the nature of comments that usually accompany National Body votes, important changes may have to be made on documents when they progress from CD to DIS and from DIS to IS. The net result is that standards produced by MPEG are of very high quality. No single error was discovered in MPEG-1 and small errors, better described as items of text of dubious interpretation, were found in MPEG-2 Video and MPEG-2 Audio. Corrections are produced using the "Corrigendum" process. In MPEG-2 Systems, Video and Audio it was found useful to introduce some new features that built upon the standards as originally released. This was done using the "Amendment" process defined by ISO. For some MPEG standards it has been found useful to produce new revisions.

Much of the technical work is done at week-long MPEG meetings. Several hundreds contributions are submitted by members by electronic means. The meeting is structured in Plenaries (4 hours on Monday morning, 2 hours on Wednesday morning and all the afternoon of Friday) and in subgroup meetings.

About 200 documents are produced at every meeting to capture the agreements reached. Particular importance assume

  • "Resolutions" which document the outline of each agreement and make reference to the documents produced, and
  • "Ad-hoc groups", groups of experts working on some specified area of work, usually until the following meeting. Ad-hoc groups work by e-mail and in some exceptional cases they are authorised to hold physical meetings.

Output documents, too, are stored on the MPEG document management site. Access to input and output documents, however, is restricted to MPEG members

Attendance at MPEG meetings requires accreditation by a National Standards Body or standards committee in liaison. Experts attending MPEG who do not represent a committee in liaison must be members of a National Delegation.

To know whom to contact in your country click here. You should make sure that you seek membership of the right committee, formally ISO/IEC JTC 1/SC 29/ WG 11 (MPEG), because national standards bodies have competence in manifold areas of standardisation.