No one, reading MPEG standards, should deny that the spectrum of MPEG standards is an impressive set of disparate technologies integrated to cover fields connected by the common thread of technologies underpinning Data Compression: Coding of Video, Audio, 3D Graphics, Fonts, Digital Items, Sensors and Actuators Data, Genome, and Neural Networks; Media Description and Composition; Systems support; Intellectual Property Management and Protection (IPMP); Transport; Application Formats; API; and Media Systems.
How are all these technologies specified and integrated in MPEG standards to respond to industry needs? This chapter will try and answer this question by starting, as many novels do, from the end (of an MPEG meeting).
When an MPEG meeting closes, the plenary approves the results of the week. This marks the end of formal collaborative work within the meeting. Back in 1990 MPEG developed a mechanism – called “ad hoc group” (AhG) – that would allow experts to continue a form of collaboration. AhGs allow MPEG experts to continue working together, albeit with limitations:
- In the scope, i.e. an AhG may only work on the areas identified by the mandates (in Latin ad hoc means “for the specific purpose”). Of course experts are free to work individually on anything and in any way that pleases them and submit their independent results at the next meeting;
- In the purpose, i.e. an AhG may only prepare recommendations – in the scope of its mandates – to be submitted to MPEG. This is done at the beginning of the following meeting, after which the AhG is disbanded;
- In the method of work, i.e. an AhG operates under the leadership of one or more Chairs. It is clear that the success of an AhG depends very much on the attitude and activity of its members.
On average some 25 AhGs are established at each meeting. There is no one-to-one correspondence between MPEG activities and AhGs. Actually, AhGs are great opportunities to explore new and possibly cross-domain ideas. Examples of AhG titles are
- Scene Description for MPEG-I
- System technologies for Point Cloud Coding (PCC)
- Network Based Media Processing (NBMP)
- Compression of Neural Networks (NNR).
What happens between MPEG meetings
An AhG uses different means to carry out collaborative work: by using email reflectors, by teleconferencing and by holding physical meetings. The last can only be held if they were scheduled in the AhG establishment form. Unscheduled physical meetings may only be held if those who subscribed to the AhG unanimously agree.
Most AhGs hold scheduled meetings on the weekend that precedes the next MPEG meeting. These are very useful to coordinate the results of the work done and to prepare the report that all AhGs must make to the MPEG plenary on the following Monday.
It should be noted that AhG meetings, including those in the weekend preceding the MPEG meeting, are not formally part of an MPEG meeting.
MPEG chairs meet on the Sunday evening to review the progress of AhG work, coordinate activities impacting more than one Subgroup and plan activities to be carried out during the week including identification of joint meetings
An MPEG meeting at a glance
During an MPEG week MPEG holds 3 plenaries
- On Monday morning: to make everybody aware of the results of work carried out since the last meeting and to plan work of the week. AhG reports are a main part of it as they are presented and, when necessary, discussed;
- On Wednesday morning to make everybody aware of the work done in all subgroups in the first two days and to plan work for the next two days;
- On Friday afternoon to approve the results of the work of Subgroups, including liaison letters, establishment of new AhGs etc.
Subgroup and Breakout Group
Subgroups start their meetings on Monday afternoon. They review their own activities and kick off work in their areas. Each subgroup assigns activities to breakout groups (BoG) who meet with their own schedules to achieve the goals assigned. Each Subgroup may hold other brief meetings to keep everybody in the Subgroup in sync with the general progress of the work.
For instance, the activities of the Systems Subgroups are currently (March 2019): File format, DASH, OMAF, OMAF and DASH, CMAF and MIAF, MPEG Media Transport, Network Based Media Processing and PCC Systems.
On Friday morning all Subgroups approve their own results. These are automatically integrated in the general document to be approved by the MPEG Plenary on Friday afternoon.
A key MPEG feature is the immediate availability of the necessary technical expertise to discuss matters that cross organisational boundaries. The speed of development and quality of MPEG standards would hardly be possible if it were not possible to deploy the necessary expertise to address multi-faceted issues in a timely manner.
Let’s take as an example this video: the basketball player is represented as a compressed dynamic point cloud in a 360ᵒ video. The issue of integrating the two components may be raised at a meeting and/or discussed by the Chairs where the need for a joint meeting is identified. This is proposed to the MPEG plenary and held with the participation of Requirements, Systems and 3D Graphics Coding experts. The outcome of such a meeting may be anything from the acknowledgement that “we don’t know well enough yet”, to the identification of technologies that can simply be developed as a collaborative effort of MPEG experts or require a CfP.
For example, the table below lists the joint meetings that the Systems Subgroup held with other Subgroups at the January 2019 meeting.
Table 3 – Joint meetings of Systems Subgroup with other Subgroups
|Systems meeting with||Topics|
|Reqs, Video, VCEG||SEI messages in VVC|
|Audio, 3DG||Scene Description|
|3DG||Systems for Point Cloud Compression|
|3DG||API for multiple decoders|
|Reqs, JVET, VCEG||Immersive Decoding Interface|
NB: VCEG is the Video Coding Experts Group of ITU-T Study Group 16. It is not an MPEG Subgroup.
The Chairs meet on Tuesday evening to assess the result of the first two days of work, review the work plan and time lines based on the expected outcomes and identify the need of new joint meetings, and on Thursday evening to wrap up the expected results and review the preliminary version of the results of the meeting.
A bird’s eye view of an MPEG meeting
Figure 7 depicts the workflow described in the paragraphs above, starting from the end of the N-1 th meeting to the end of the N-th meeting.
Figure 7: MPEG work from the end of a meeting to the end of the next meeting
What is “done” at an MPEG meeting?
There are around 500 of the best worldwide experts attending an MPEG meeting, an event that mobilises an incredible amount of brain power. The following explains how this brain power is directed.
An example – the video area
Let’s take as example the work done in the Video Coding area at the March 2019 meeting by looking at the 3 columns of Table 4:
- The standards on which work is done (currently Video works on MPEG-H, MPEG-I, MPEG-CICP, MPEG-5 and Explorations)
- The names of the activities
- The types of documents resulting from the activities (see the legend after Table 4 for an explanation of the acronyms).
Table 4 – Documents produced in the video coding area
|H||High Efficiency (HEVC)||TM, CE, CTC|
|I||Versatile Video Coding (VVC)||WD, TM, CE, CTC|
|3 Degrees of Freedom + (3DoF+) coding||CfP, WD, TM, CE, CTC|
|CICP||Usage of video signal type code points (Ed. 1)||TR|
|Usage of video signal type code points (Ed. 2)||WD|
|5||Essential Video Coding||WD, TM, CE, CTC|
|Low Complexity Enhancement Video Coding||CfP, WD, TM, CE, CTC|
|Expl||6 Degrees of Freedom (6DoF) coding||EE, Tools|
|Coding of dense representation of light fields||EE, CTC|
|TM||Test Model, software implementing the standard (encoder & decoder)|
|CE||Core Experiment, i.e. definition of and experiment that should improve performance|
|CTC||Common Test Conditions, to be used by all CE participants|
|CfP||Call for Proposals (this time no new CfP produced, but reports and analyses of submissions in response to CfPs)|
|TR||Technical Report (ISO document)|
|EE||Exploration Experiment, an experiment to explore an issue because it si not mature enough to be a CE|
|Tools||Other supporting material, e.g. software developed for common use in CEs/EEs|
The outcome of an MPEG meeting
Figure 8 gives the number of activities for each type of activity defined in the legend (and others that were not part of the work in the video area).
Figure 8: Activities at an MPEG meeting
For instance, out of a total of 97 activities:
- 29 relate to processing of standards through the canonical stages of Committee Draft (CD), Draft International Standard (DIS) and Draft International Standard (FDIS) and the equivalent for Amendments, Technical Reports and Corrigenda. In other words, at every meeting MPEG is working on ~10 “deliverables” (i.e. standards, amendments, technical reports or corrigenda) at different stages of the approval process;
- 22 relate to working drafts, i.e. “new” activities that have not entered the approval stages;
- 8 relate to Technologies under Consideration, i.e. new technologies that are being considered to enhance existing standards;
- 8 relate to requirements, typically for new standards;
- 6 relate to Core Experiments;
Figure 8 does not provide a quantitative measure of “how many” documents were produced for each activity or “how big” they were. As an example, Point Cloud Compression has 20 Core Experiments and 8 Exploration Experiments under way, while MPEG-5 EVC has only one large CE.
An average value of activity at the March 2019 meeting is provided by dividing the number of output documents (212), by the number of activities (97), i.e. 2.2.
MPEG holds quarterly meetings with an attendance of ~500 experts. If we assume that the average salary of an MPEG expert is 500 $/working day and that every expert stays 6 days (to account for attendance at AhG meetings), the industry investment in attending MPEG meetings is 1.5 M$/meeting or 6 M$/year. Of course, the total yearly investment made by the industry is more than that.
With the meeting organisation described above MPEG tries to get the most out of industry investment in MPEG standardisation.
|Table of contents||◄||5.1 The MPEG organisation||█||5.3 How MPEG develops standards||►|