Telecommunication Standardization Sector	Document AVC-496R
Study Group 15	April 7,  1993
Experts Group for ATM Video Coding	
(Rapporteur's Group on Part of Q.2/15)

Source	: CHAIRMAN OF THE EXPERTS GROUP FOR ATM VIDEO CODING
Title	: REPORT OF THE ELEVENTH MEETING IN SYDNEY AND MELBOURNE
	  (March 27 - April 7, 1993)
Purpose	: Report

-----------------------

Contents

1. 	General
2. 	Documentation
3. 	Tape demonstration
4. 	Review of the previous meetings
5. 	Joint sessions with MPEG in Sydney
6. 	Source coding
7. 	Network aspects
8. 	Work plan
9. 	Others

1. General

The eleventh meeting of the Experts Group was held in Australia as follows;

- 	Joint sessions with ISO/IEC JTC1/SC29/WG11 (MPEG) in Sydney during March 29 - April 2, 1993 at the kind invitation of Standards Australia,
- 	TSS sole sessions in Melbourne during April 5 - 7 at the kind invitation of Telecom Australia.

At the opening of the joint sessions in Sydney, Mr. John Burton (General Manager, Business Strategy Telecom Australia) made a welcoming address to MPEG and TSS EG members on behalf of the hosting organization.  At the opening of the sole sessions in Melbourne, Mr. Ray Ligett (Director of Research, Telecom Australia) welcomed TSS EG members on behalf of the hosting organization.

At the end of the sole sessions, Chairman thanked the hosting organizations for the meeting facilities provided and the excellent secretarial support.  

The list of participants appears at the end of this document. 

2. Documentation (TD-2)

For the sole sessions, 53 AVC-numbered documents and 16 Temporary Documents have been made available as listed in Annex 1.  Annex 1 also includes a list of documents for the joint sessions.

3. Tape demonstration (TD-3)

Several video tape demonstrations were given in D1 format to present experimental results as detailed in Annex 2 .  

4. Review of the previous meetings 

4.1 World Telecommunication Standardization Conferences (TD-8)

Mr. Zedler outlined the outcome of WTSC-93 held in Helsinki, particularly new structure of ITU focusing on Study Group 15 of Telecommunication Standardization Sector.

4.2 Torino/Roma meeting (AVC-443R,444R)

The meeting shortly reviewed the outcome of sole and joint sessions in Italy.

4.3 CMTT/2 and its SRG

Mr. Zedler introduced current activities of CMTT/2 and its SRG.  The meeting recognized the need to have closer relationship looking at the fact that CMTT is now SG 9 in the same TSS umbrella.

4.4 Regional coordination meeting on March 28 (TD-6)

According to the agreement at the Roma closing session, a coordination meeting was held on March 28 to check if there are any contentious matters from TSS's point of view toward the joint sessions.  Its report is contained in Annex 3 to this document.

5. Joint sessions with MPEG in Sydney

5.1 Requirements (TD-7)	reported by A. Tabatabai, S. Okubo

The REQUIREMENTS sub-group met every day during the week (March 29 - April 2) under chairmanship of Sakae Okubo.  In addition to our own sessions, we had joint sessions with other sub-groups as follows;

-	with VIDEO and IMPLEMENTATION, 9:00 - 10:50 on Tuesday to identify open issues regarding the Main Profile at Main Level,
-	with VIDEO, 9:40 - 11:35 on Wednesday to have free discuss on other profiles than Main,
-	with SYSTEMS, 12:05 - 13:10 on Wednesday to review the "Guide for Systems Work" document,
-	with VIDEO, 9:30 - 11:30 on Thursday to review the study results on open issues for Main Profile at Main Level and features of NEXT Profile,
-	with AUDIO, 16:30 - 17:00 on Thursday to finalize the "Guide for Audio Work" document.

	5.1 1 Background

		5.1.1 1 Relevant documents

N0349	Okubo	MPEG/Requirements meeting report (Rome)	
N0363	REQ sub-group	Definition of Profiles and the Main Profile	

		5.1.1.2 Discussion

The meeting started this week discussion with a short review of what happened in the previous Rome meeting and identified items to be worked out at this meeting.

	5.1.2 WD

		5.1.2.1 Relevant documents

93/305	Savatier	Comments on MPEG-2 Working Draft Version 3	
93/334	Kogure	Report of ad-hoc group on MPEG-2 Video WD development	
93/423	WD Editing C.	MPEG-2 Working Draft (Video Part), Version 3	
93/479	Editorial group	First Working draft	

		5.1.2.2 Discussion

The meeting reviewed the profile related parts in WD Version 3, and concluded that informative description of the current clause 6 should be moved to subclause 0.3 and normative description to clause 9.  Mr. McCann and Mr. Williams drafted instructions for WD editing which were incorporated in the updated version.

	5.1.3 Main Profile at Main Level

		5.1.3.1 Relevant documents

93/267	NNI	Resolutions of the Dutch National Body NNI for the MPEG meeting in Sydney	
93/269	UKNB	List of open issues in MPEG-2 Main Profile	
93/319	Wise	Various issues in MPEG-2	
93/369	Dunstan	Data partitioning and the main profile	
93/376	Corset et al.	Proposal for a 1.75 Mbit max. vbv_buffer for the main profile	
93/392	UKNB	Resolutions from the UK	
93/396	TSS/J	Syntax modifications for VBR operation	
93/424	AFNOR	French contribution to the meeting in Sydney	
93/433	Koster	Harmonising/combining low complexity, error resilience, scalability, image quality and compatibility	
93/439	ITU-RS TG 11/4	- Comments to Main (Core) Profile of MPEG-2
- The number of active lines for distribution of 525 line signals	
93/448	Req. group	List of open issues for main profile at main level	
93/472	Req. group	Reply to open issues	
93/481	MPEG/Req.	Liaison statement from MPEG to Radiocommunications TG11/4	

		5.1.3.2 Discussion

The meeting first listed open issues for the Main Profile at Main Level from the requirements point of view as summarized in MPEG93/448 based on several input documents as well as interaction with VIDEO and IMPLEMENTATION.  Then we studied them item by item, paying attention to the CCIR requirements presented by Mr. Nishizawa and Mr. Bedford (MPEG93/439) and concentrating on the following;

-	support of forward/backward compatibility,
-	layered coding for error resilience and hierarchical representation,
-	number of coded lines for 525/60 television systems.

		5.1.3.3 Agreements

Views of the REQUIREMENTS sub-group for the open issues regarding the Main Profile at Main Level were summarized as in MPEG93/472.  Highlights are listed here.

		a. Compatibility

We recommend that Main Profile at Main Level decoders should be able to handle MPEG-1 constrained parameter bitstreams.

Backward compatibility is not supported by the Main Profile.  Backward compatibility is to be supported by the spatial scalability in other profiles.

		b. Layered coding

The hierarchical/scalable feature should be included in a new profile together with 4:2:2.

To cope with uncorrected bit errors or cell losses which may come through even the error protected channel or storage media, the video source decoder should be modestly error resilient with cost effective means.  If we have to cope with higher cell losses (e.g. higher than 1E-3 at 4 Mbit/s), layered coding by using prioritized channels is effective.  Possible solutions are scalable coding, and data partitioning.  This feature should be considered as a part of new profiles.

Related to this discussion, the meeting agreed to drop the definitive wording for Main Profile from WD because it is not suitable for external use.

		c. Number of coded lines for 525/60 television systems

After extensive discussion in the REQUIREMENTS sub-group and consultation with the IMPLEMENTATION sub-group, the meeting reached a conclusion that 480 lines are appropriate for Main Profile at Main Level and his feature should be considered in the design of new profiles together with other features addressed by CCIR.

		e. profile_and_level_ID

To cope with undefined number of profiles and levels, we suggest the structure of "1 bit escape + 7 bit information" and 7 bits to consist of 3 bits profile ID and 4 bits level ID.

		f. Decoder resource related indications

We recommend these should not be separately included in the syntax, but should be covered by Profile_and_Level indication.

		g. Liaison response to Radiocommunication sector TG11/4

The meeting decided to return response as in MPEG93/481 to the CCIR's concern expressed in MPEG93/439 

	5.1.4 Other Profiles and Levels

		5.1.4.1 Relevant documents

92/714	Stevens et al.	Application profile for desktop video conferencing	
93/238	Lippman	Suggestion for a revised set of profiles	
93/253	PTT Research	Interworking and complexity requirements on scalable video coding algorithms	
93/294	Urano et al.	Consideration for EDTV(progress) from the viewpoint of MPEG-2 profile/level	
93/314	Sikora	Evaluation of scalable coding schemes	
93/339	JNB 	Proposal for MPEG-2 video profiles	
93/427	Yamada et al.	Multiple profiles and informative profiles proposal	
93/477	Teichner	Compatibility between chrominance formats 4:2:2 and 4:2:0	
93/450	Koster	Attempt for the definition of the new  profile, with the HDTV and TV levels	
93/473	REQ sub-group	Profile architecture	

		5.1.4.2 Discussion

The meeting studied profiles other than Main which need be defined in addition to the Main.  At the joint session with VIDEO, the following features were listed as tools additional to those for the Main;

-	data partitioning; graceful degradation on different channels
-	scalability; satisfying the need of multimedia computers
-	multi-layered broadcasting; compatible HDTV
-	F/F and more; advanced random access for storage applications
-	shorter random access and channel hopping; switching time for channel coding should also be taken into account
-	lower delay
-	symmetric coding/decoding for camcorders and VCR; inexpensive solutions

Taking into account these and other suggestions contained in the input documents, we first focused on a profile (called NEXT for brevity) which has more functionalities than the Main, hierarchical representation in particular, and are appropriate for terrestrial broadcasting and information technology.  Following the practice for development of the Main Profile, we worked to make a skeleton for this new profile by describing purpose, key functionalities, performance and open issues.  

An implication of this new profile is that there may appear complex situations for compatibility between MAIN and NEXT encoders and decoders.  We discussed extensively possible interoperability scenarios and reached a common understanding that care should be taken to reduce the number of combinations.

There were also expressed interests for low cost version of MAIN.  The meeting spent some time to consider this profile as well (called SIMPLE for brevity) and obtained a short description of its skeleton.

Finally, the meeting studied the whole picture of profiles and levels to map MAIN, NEXT and SIMPLE profiles and to identify the remaining areas of further study.  Mr. Lippman pointed out that hardware constraints would lead to products which conform to both lower profile at higher level and higher profile at lower level.

At the joint session with VIDEO, we also discussed on the comparison between spatial scalability and frequency scalability.  This action is based on the guideline that the standard should not contain two or more tools for the same purpose.  This time the objective was mostly to initiate the work, awaiting further contributions to allow early decision.

		5.1.4.3 Agreements

The outcome of the profile study was formulated as MPEG93/473 (see Annex 4 to this document) which shows mapping of subsets of the whole MPEG-2 video standard in terms of profile and level as well as skeletons for NEXT and SIMPLE profiles.  This document also indicates issues to be solved.

As part of the interworking scenarios, the meeting considered 4:2:2 and 4:2:0 compatibility and agreed to make the following recommendation of the group to ease the complexity; the REQUIREMENTS sub-group recommend that the VIDEO sub-group incorporates all necessary means to support up- and downward compatibility between 4:2:2 and 4:2:0 chroma formats.

		5.1.4.4 Adhoc group

In order to progress The meeting agreed to establish an Ad-hoc group on other Profiles and Levels which is mandated to elaborate description of Profiles and Levels other than Main based on the skeletons obtained at the Sydney meeting.  Mr. B.G. Haskell volunteered to chair this adhoc group.

	5.1.5 Presentation related indications

		5.1.5.1 Relevant documents

93/298	Penney	Syntax for MPEG-2 colorimetry and transfer characteristics	
93/356	Wells	Requirement for PAL phase information	

		5.1.5.2 Discussion

The meeting reviewed the discussion in Rome and recommended that the syntax include a mechanism to accommodate future addition of other indications.

	5.1.6 Requirements for Systems

		5.1.6.1 Relevant documents

N0364	REQ group	Guide for Systems work, Rome revision	
93/260	Giachetti	Access control requirements on the broadcast multiplex structure	
93/316	Curet	A frame oriented broadcast-multiplex with different levels of protection	
93/322	Bache et al	General multiplexing requirements for a digital TV broadcast operator	
93/439	ITU-RS TG11/4	Comments on "Liaison letters to BR SRG on user requirements" especially on "Systems requirements"	
93/471	REQ group	Guide for Systems work, Sydney revision	

		5.1.6.2 Agreements

At the joint session with SYSTEMS, the meeting adopted a couple of revisions to the Rome version as in MPEG93/471.

	5.1.7 Requirements for Audio

		5.1.7.1 Relevant documents

93/245	REQ group	Guide for the Audio Work Group	
93/337	Brandenburg	Report of Ad-hoc group for new Audio Work Project description and requirement listing	
93/338	Rabowsky	Report of Ad-hoc group on guide for MPEG2 Audio work	
93/462a	REQ group	Guide for the audio work	

		5.1.7.2 Agreements

At the joint session with AUDIO, the meeting adopted the normative description of MPEG-2 audio requirements as in MPEG93/462a.

	5.1.8 Informative Requirements listing

		5.1.8.1 Relevant documents

92/674a	REQ. group	Information on requirements for MPEG-2	

		5.1.8.2 Discussion

There was no input at this meeting to update the document.

	5.1.9 Verification tests

		5.1.9.1 Relevant documents

93/259	Hidaka	Summary of MPEG-2 verification test	
93/331	Hidaka	Report of Ad-hoc group on MPEG-2 verification test	
93/445	Nasse	Letter to Mr. Hidaka	

		5.1.9.2 Discussion

Mr. Hidaka presented the current status of verification testing plan focusing on bitstream interchange and picture quality assessment.  The latter is going to be carried out with obtaining cooperation of EBU, CCIR and SMPTE.  The meeting discussed for short time on how to verify other aspects of the standards; various functionalities in particular.  Due to lack of time, the meeting decided to continue this work through correspondence in an adhoc group.

		5.1.9.3 Adhoc group

The meeting agreed to establish an adhoc group on requirements for the verification test which is mandated to list test items necessary for verification of the draft standard with respect to bitstream interchange, functionality and performance.  Mr. Teichner volunteered to chair this adhoc group.

	5.1.10 Very low bit rate audiovisual coding

This session was intended to review the state of the arts for very low bit rate audiovisual coding to prepare for the new project (MPEG-4).  The following was presented for this purpose;

-	Mr. R. Schaphorst: report of the first meeting of his LBC group in ITU-TS SG 15 (MPEG93/421)
-	Mr. J. Ostermann: video coding based on object oriented analysis-synthesis
-	Mr. M. Yano: hybrid coding using MC + orthogonal transform of arbitrary shape (MPEG93/469 with tape demonstration)
-	Mr. J-H. Jeon: hybrid coding using MC + DCT (MPEG93/436)
-	Mr. B. Haskell: report of PCS'93 and information on relevant workshops etc.

In the course of free discussion on how to organize the standardization work, it was recognized that good audio and video test materials typical for MPEG-4 applications would facilitate the study.  Members are requested to provide such test materials.

Mr. Haskell suggested to take the competitive and collaborative approach for this new project.  There was also raised a question what would be yardsticks for evaluating implementation complexity.

It was a common understanding that some drastically new techniques are required to achieve the objective and that interdisciplinary interaction would help us.  The meeting suggested hold a workshop for this purpose during the next meeting in New York, inviting researchers from computer vision, psychology, music synthesis, speech synthesis, etc.  Messrs. Kogure, Osterman, Haskell undertook to act as regional contact points.

5.2 Video	reported by G. Bjoentegaard

The video group met throughout the week.  No subgroups were formed - except for those working on the final version of the syntax.  The video group had joint sessions with implementation, requirements and systems.

	5.2.1 Open issues for main profile.

Several core experiments related to the main profile were still performed up to this meeting.  One of the main issues in the video group was therefore to draw conclusions from these experiments and make proposals for the main profile.  The outcomes from the reviews are listed below.

	a. Transform:  Only 8x8 DCT is allowed.

	b. AC Leak:  Not supported by main profile.

	c. Block size for motion vector

There were experiments to test 16x8 prediction blocks for frame structure pictures.  This was dropped.  Only 16x16 blocks are allowed for prediction in frame structure pictures.

	d. Smart prediction

Only Dual-Prime is allowed as smart prediction - and only for M=1.  Since M is undefined in the WD, the exact definition was not quite clear.  The understanding was "local M=1" which means that the decoder receives successive I or P pictures.

	e. Skipped pictures

Skipping of pictures to obtain low delay is allowed only for M=1.  The definition of "M=1" is similar to the definition for smart prediction.  There is no picture type for skipped picture.  The decoder will receive information on which pictures are skipped from the temporal reference parameter.

	f. IDCT mismatch

A new method for oddification of reconstructed transform coefficients was proposed (MPEG93/278).  This was adopted as a new oddification rule.

	5.2.2 Syntax and working draft

The other main issue at this meeting was to produce a complete working draft.  Since the main element of the WD is the syntax,  much work was spent on this.  Keywords in this work were :

-	Simplify.
-	Clean up.
-	Tune to the outcome of core experiments.

This work seemed successful.  The resulting syntax is much cleaner than the old one.  The result may be seen in the "WD Video".

	5.2.3 Scalability

All the core experiments on scalability continue.  For spatial scalability there are no new experiments, whereas frequency scalability has two new core experiments (see TM5).  There is still an effort to merge all the scalable approaches.  This is subject for further discussion.

	5.2.4 New profiles

The video group spent practically no time on this issue.  At the moment it is considered to be mainly a requirements issue.

Generally, the video group succeeded in its task to finalising the open issues for the main profile and to produce a WD.

5.3 Systems (TD-9)	reported by B.G. Haskell, C.J. McGrath

The MPEG 2 Systems sub group met each day during the Sydney meeting of WG11, 29 March to 2 April, 1993.  In addition, the ad hoc group established in Rome to manage the writing of the working draft met on Sunday 28 March to continue the discussion and convergence process.

Significant achievements of the week include:

-	Approval of a Working Draft Document for MPEG 2 Systems
-	Establishment of an AdHoc Group to continue Working Draft revisions
-	Meetings set for Atlanta (May 1993) and Brussels (June 1993)
-	Establishment of an AdHoc Group to study MPEG Systems / ATM AAL issues
-	Approval of "Response to TSS concerning relationship of MPEG Systems to ATM AAL; Document WG11 N0399 is attached.

A high level view of MPEG systems was generated by the group during the week indicating the assumed interactions between MPEG 1 elemental and Program Streams (MPEG - 1 PS), MPEG 2 program streams similar to MPEG 1 streams (MPEG 2 PS), both of which are oriented toward error-free environments such as DSM.  The diagram also covers presumed conversions between these Program Streams and MPEG 2 transport streams, presumed to be used for multiple (1 or more) transport of MPEG 2 elemental and program streams in transport environments which typically introduce errors(error-full).

Significant discussion during the week focused on the ease of conversion between the various formats, Program Streams and Transport Streams.  There is a simultaneous desire to maintain simplicity and economy in the definition of MPEG - 2 TS streams and to permit a maximum number of applications to be fully defined by the standard.  Achieving appropriate balance in this task continues to consume a significant percentage of the groups time.

The issue of overlap among MPEG "layers" of formatting and equivalent (in protocol stack terms) ATM adaptation layers was given considerable consideration, although no firm agreements were reached.  An ad hoc was established to specifically address these issues.

The "Guidelines for Systems Work" from Requirements was revised slightly in a joint Systems/Requirements meeting on Wednesday.(MPEG 93/471).

5.4 Implementation	reported by P. Stevens, G. Morrison

Sessions were held throughout the week of 29 March to 2 April.  The core participants were:

Geoff Morrison	BT Labs (chair)
Doug Bailey		IIT
Steve Haigh		InovaCom
San Narasimhan	IME Singapore
Chadd Fogg		Cascade
Jong Cheul Park	Kaitech Korea
Yasumori Ishikawa	Ricoh Co.
Barth Canfield	TCE
John Gooding	Phoenix VLSI Consultants
Marco Gandini	CSELT
Hock Gin Lim	Monash University Australia
Paul Chiang		Texas Instruments
Thierry Fautier	Philips LEP

The major task was to deal with all open issues so that the Video WD for Main Profile Main Level could be frozen at the end of the week.  In the afternoon of 29 March a list of these was draw up.  This list was then exchanged with similar ones from the Video and Requirements subgroups to pick up all relevant open issues for each subgroup.

The list of open implementation issues and the conclusions reached on them during the week was documented in MPEG 93/466 as attached.

The subgroup also prepared its recommendations.  These are documented together with those of all the WG11 subgroups in the convenor's report.

ISO/IEC JTC1/SC29/WG11
MPEG 93/466
1 April 1993

Source:	Implementation Studies subgroup
Title:	Open Issues - Implementation

This document lists the open issues pertinent to the Implementation Studies subgroup identified on 29 March 1993 and the conclusions on them by the afternoon of 1 April 1993.

It must be borne in mind that the assessment of  cost/complexity is not based on a single implementation but on consensus over several.  Consequently for any specific implementation it is possible that the conclusions given below appear inconsistent.

Localised Questions - Global review needed
We  point out that many of the features considered do not individually result in a large cost increase (eg in silicon area).  However, the sum total is significant and more importantly, the verification and test cost will depend on the number of permutations of the ways in which a block can be coded.. This is the reason for recommending against coding options and combinations of coding options which give only small benefits.

Dual Prime (MPEG 93/393)
Cost effective design requires a datapath. The processing of dual prime adds a great deal of complexity into the datapath and increases the size, cost, speed and buffering in programmable type solutions.
Recommend:-Dual Prime limited to I, P or removed.

Alternate Scanning (MPEG 93/318, /393)
Is this simply a cover for encoders that cannot make frame field decisions properly?
Increases complexity, but not greatly.
Recommend:- Investigate linking scan path decision and VLC table to frame/field coding bit.

Adaptive VLC
Puts additional constraints on certain implementations. This is especially difficult for software only implementations, necessitating additional tests and branches for each coefficient.
Hardware decoders require faster 'Level' decode circuits and an extra feedback path.
Recommend:- Macroblock flagged OK, self adaptive is expensive, not OK.

Priority Break Point (MPEG 93/312, /369)
It is clear that the priority breakpoint adds significant complexity in normal play modes. It is also clear that FF and error resilience are enhanced by the addition of the PBP. However, it not clear whether the FF and error resilience are requirements of the Main Profile and the Implementation Studies group requests clarification from the Requirements group before proceeding.  By constraining the syntax locations pointed to by PBPs it may be possible to reduce the complexity of the scheme.
Recommend:  No change to Rome meeting recommendation (main profile decoder able to decode one partition.)

Mixed frame field structures
Accepted at Rome meeting.
Recommend:  Rectify believed problem with WD page 30 line 14 (Fautier).  Clarify Temporal Reference for frame/field.  Clarify whether structures such as the following are permitted:

I B B P		(This might occur in edited bit streams)
 x B B I

Oddification
We examined two proposals for a new oddification technique.  Neither method was preferable in both hardware and software decoder implementations.  One method (SONY) was judged to be much preferable in hardware implementations.  The other (GCT) has some advantage for software decoders.  On balance the former method was selected.  The exact modification of the final coefficient needs to be specified.
Recommend:  If the MPEG-1 oddification is not adequate, then the technique in document 93/278 be adopted and oddification should be performed by inverting the least significant bit of the (7,7) coefficient.

3:2 pulldown
The general principle of indicating repeated uncoded fields (of which 3:2 pulldown is a specific example) is accepted.
Recommend:  General method be part of complete syntax, preferably unified with skipped pictures.  VBV section may also require revision.

"PAL bits"
These are perceived as having virtually zero impact on decoders.  Relevant data will merely be made available to subsequent processes or ignored.
Recommend:  No further action

Huffman (MPEG 93/320)
We were requested to choose between two VLC tables for Intra coefficients.  Neither of these were fully acceptable to the Implementation Studies subgroup.  Document 320 pointed out that the shorter of the two does not obey certain construction rules which aid some implementations.  Other implementators preferred the shorter table.  A proposal to allow partially downloadable VLC (programmable lengths but fixed ordering of events) was made by some members.
Recommend:  Video subgroup consider proposal by Bailey et al.  If not acceptable, Video subgroup to decide between existing two tables.

Chroma post processing flag
It is understood that this information is advisory only and decoders may ignore.
Recommend:  WD be clear on this point.

Leaky prediction
The main penalty here is the temporary storage of 64 pels while computing the DC component.
Recommendation:  Not have leaky prediction.

Hardware verification
Opinion was that we could not do more than will happen anyway.
Recommend:  No further action.

Buffer size
Video subgroup advised 1.75 Mbit
Recommend:  No further action.

NTC
Withdrawn in Video subgroup.
Recommend:  No further action.

MPEG-1 superset (MPEG 93/319)
Video subgroup has adopted principle of MPEG-2 being superset of MPEG-1.
Recommend:  No further action.

8 by 1 DCT
This has non-zero cost because of changed pipelining problems arising from change of latency between 8 by 8 and 8 by 1, the impact on quantisation from changed range, changed scanning order and flow of quantisation weights.
Recommend:  8 by 1 DCT not be included in MPEG-2 unless worthwhile visual improvement.

16 by 8 frame structure
Was discussed in Rome meeting and recommendation made then to exclude 16 by 8 frame.  Flexibility of frame/field requires references stored as fields.  16 by 8 frame leads to 16 by 4 (and 8 by 2 chrominance) accesses which have high overhead.
Recommend:  No change to previous position of no 16 by 8 frame.  

Escape codes
New proposed 13 bit escape leads to 31 bit long codewords.  (The 13 bit code is also not of arithmetic construction.)  These can be troublesome in decoders, especially when many occur consecutively or with little spacing.
Recommend:  6 bit escape plus run plus 12 bit level selected permanently on MPEG-2.

MQUANT
We were informed of a new non-linear QUANT table agreed by concerned members of the Video subgroup.  This four part piece-wise linear law is reasonably amenable to computation.
Recommend:  Incorporate this table in WD as only alternative to MPEG-1 table.  Use of only one table preferred, eg new table always for MPEG-2.  If switched, should be at high layer in video multiplex, ie picture header or above.

Impact of 486 lines versus 480 (MPEG 93/455)
The sentiment expressed in document 455 is that for at least the initial years, economically viable decoders will depend to some extent on statistics of encoded real pictures and will not be able to fully decode worst case bit streams.  The probability of such a decoder running out of memory bandwidth increases as more memory cycles are required for larger pictures.  Close to the knee, small increases in picture size can have a large effect on the probability of the decoder having insufficient memory bandwidth.  Field/frame structures mean that the next effective value (for memory bandwidth considerations) above 480 is 512.
Recommend:  Main profile remains limited to 480 lines at 29.97 Hz (and 4:2:0).

Non-contiguous slices
Disallowed by Video subgroup
Recommend:  No further action.

Extension data identification (MPEG 93/319)
There was support for this.
Recommend:  Add to syntax.

Excessive conditional syntax (MPEG 93/319)
There was support for this.
Recommend:  At higher levels of video multiplex where bit consumption is not high, conditional inclusion of data should be removed from syntax.

Vector coding (MPEG 93/319)
The video group decided to retain the MPEG-1 motion vector coding method.
Recommend:  No further action.

Picture dimensions and slice vertical position (MPEG 93/275, /319)
Requirements sub group has decided that picture dimensions are limited to 16 K (14 bits).  Proposals made in these two contributions for handling pictures larger than is possible with MPEG-1 have no impact on main profile, main level decoders.  They are OK for implementations.
Recommend:  Video subgroups select one and include in syntax. 

Sequence header and GOP (MPEG 93/275, /319)
Already under consideration by Video syntax editing group.

Signalling of resource requirements (MPEG 93/319)
There was support for this concept.
Recommend:  Requirements subgroup requested to consider with view to asking for inclusion in video WD.

Syntax cleanup
Underway within Video subgroup.

Skipped pictures
Need clarification whether skipped pictures are only in low delay node or are possible with 'B'.  Issue of whether headers for skipped pictures are included or not - may be preferable for decoders to aid in distinguishing between skipped and loss situations.
Recommend:  Additional text required in WD?

5.5 TM5 (AVC-445b,491b)

	5.5.1 Addition to TM5

Mr. Koster presented AVC-491 "Test Model 5" as outcome of the Sydney meeting, highlighting new experiments and pointing out that overlap with WD has been avoided.  There were comments that the following need be further incorporated;

•	to resurrect the spatio-temporal weighting experiment (Mr. Ueno),
•	to include Experiments I.14 (Mr. Sikora),
•	to update low delay description reflecting the frozen specifications (Mr. Bjoentegaard).

These and other modifications were included in the second version of TM5 (AVC-491b) which was distributed by Mr. Koster during the Melbourne meeting.

	5.5.2 Test sequences typical for videophone/videoconferencing at 1-2 Mbit/s

Mr. Tabatabai raised a question whether current test sequences are appropriate for studying application of videophone and videoconferencing at lower bit rates.  Susie is deemed too easy, and others too difficult and unlikely.  The following was suggested as candidates;

•	split-screen,
•	desktop videoconferencing (graphics + conferees),
•	panning and zooming of conferees.

Immediate actions were not decided, but Mr. Schaphorst offered to demonstrate at the next meeting NTSC analog test pictures which T1A1 is to use for the video quality assessment.

5.6 WD (AVC-449,492)	S. Okubo

The WD refinement process and outcome were briefly presented.

6. Source coding

6.1 Prediction/quantization (AVC-453,488)

Experimental results were presented on 8x1 DCT and SVMC; neither was adopted in Main but the former was maintained in the TM at the joints sessions in Sydney.

6.2 Low delay mode (AVC-450,451,481; TD-10)

	6.2.1 Input documents

Three AVC documents addressed the following;

•	reference pictures when picture skipping involved,
•	VBV operation and vbv_delay setting for skipped pictures,
•	provision for low bit rate operation.

	6.2.2 Low delay operation

After having reviewed the outcome of the Sydney joint sessions represented in WD and TM5, the meeting felt it necessary to further clarify the relevant encoder/decoder operations.  It was confirmed that picture skipping is allowed only in local IPPP... environments and that M=2 field structure coding is ruled out for low delay operation as two fields should be now in pair, thus M=2 exceeds the criterion for total of reordering and buffering delay (see §H.1.1/AVC-445b).  It was also pointed out that the current VBV description would need an additional specification on the maximum number of bits per picture.

Mr. Bjoentegaard undertook to draft necessary clarification on the WD description on the above matters and produced a summary as in TD-10.  At the final session, the meeting reviewed this draft and commented that the specifications should be such that the decoder need not distinguish between low/high delay and with/without picture skipping.  Mr. Morrison suggested that an only extension from the MPEG-1 specification is to make picture extraction conditional on a complete picture being available in the VBV buffer.

The meeting agreed on the procedure that Mr. Bjoentegaard will redraft the clarification to get approval through correspondence after the meeting and put it forward to the WD Editing Committee.  See the outcome in Annex 5.

The following items await further study;

•	compliance test specification for the low delay mode operation,
•	Time Stamps for "large" pictures.

	6.2.3 Low bit rate operation

The meeting discussed the items raised in AVC-481 concerning low bit rate operation which involves regular picture skipping.  The meeting reached common understanding that the temporal reference should be according to the source picture number as described in §H.1.1/AVC-445b.

A pending issue is how to indicate limited decoding capability such as 10 Hz picture rate.  Since decoders of Main Profile at Main Level can handle up to 30 Hz picture rate, this may need definition of a new Level.  In audiovisual communications, negotiation between decoder and encoder will be needed as in the case of H.261.

6.3 Error resilience

	6.3.1 AC-leaky prediction (AVC-454,455,456,485)

Experimental results were presented on the leaky prediction addressing;

•	picture quality and coding efficiency,
•	temporal localization of error,
•	channel hopping.

They show comparable coding performance with non-leaky coding, improvement of cell loss resilience and faster channel hopping time.  Some members stated that starting with blocky pictures after a channel change in AC-leaky prediction may not be preferred.  The overall evaluation, however, depends on the trade-off between several requirements.  Mr. Haskell drew attention of the meeting to that CCIR would provide prioritization of those requirements and make input for required delay and channel hopping time at the next meeting, and indicated that AT&T would provide some trade-off consideration.

The meeting encourages members' effort to make SNR values closer among experimenters; methods of rate control and intra/inter selection need be clarified.

	6.3.2 Data partitioning (AVC-458,472,476,490,495; TD-11)

Three experimental results were presented in AVC-458,472 and 490 which indicate improvement of cell loss resilience performance with data partitioning compared to the single layer scheme.  AVC-476 gave a proposal to include two layer partitioning in the Main Profile which was rather decided to be a possible feature of NEXT Profile at the joint sessions.  AVC-495 listed information to be carried in Systems Layer to support multi-layer video coding.

The meeting was concerned with necessary provisions inside and outside the video decoder to achieve this data partitioning, or more generally layered coding.  It was felt necessary to make illustration of a total system and interactions between protocol layers for utilizing data partitioning.  Note that some related description is given in AVC-490.

Mr. Morrison undertook to coordinate a small group to further discuss this aspect and produced a report as in Annex 6.  Members are requested to make a complete picture of data partitioning based on this outcome.

The meeting recalled that high priority channel should be modeled as CBR in B-ISDN to achieve very low cell loss rate and that use of CLP requires controlling both the high priority (CLP=0) flow and the aggregate (CLP=0+1) flow to obtain desired QoS.  These should be taken into account when we carry out error resilience experiments (see §L.3/AVC-491b for rate control in the data partition experiments).

Mr. Morrison commented that the term "partition" be carefully used since this English word means that "one partition makes two or more parts".

	6.3.3 Adaptive slice size (AVC-471)

Experimental results were presented on the cell loss resilience performance of adaptive slice size technique which varies the number of macroblocks within a slice to match the length of a slice to a multiple of the cell payload length.

The meeting recognized that interaction between AAL and user layers be studied, particularly when stored video data are transmitted through ATM networks.

	6.3.4 Error on multiplexed bitstream (Annex 2 to AVC-463)

Impact of errors at the multiplexed bitstream on video reconstruction were discussed, resulting in the following;

•	Impacts of "Type 2 errors" may be translated into probability increase of "Type 1 errors".
•	How to cope with errors is not a matter of standardization.
•	The issue is the method of experimentation; whether we are not underestimating the impact of errors.  Current experiments are assuming "Type 1 errors".

	6.3.5 WD informative text (AVC-473,477)

Current status of the text development for error resilience techniques was presented including additional material for layered coding.  Members of the TSS Experts Group are strongly requested to contribute to completing this work since this is an areas of our prime concern.

After some discussion, the following was agreed;

•	to include concealment by use of neighboring macroblocks 
•	to indicate sets of combination for applicable range of cell loss rate
•	to provide text on 
-	basic intra picture/slice technique (Mr. Bjoentegaard)
-	use of intra motion vector (Mr. Biggar)
-	short slices, adaptive slice sizes (Mr. Sakai)
-	to add scalability for layered coding (Mr. Dunstan, perhaps editor's note only at this moment)

6.4 Scalability

	6.4.1 Spatial scalability

	a. Quantization for compatible macroblocks (AVC-460,480)

Both documents support no change from the current TM specifications in this respect.  The meeting was in agreement with this conclusion.

	b. Coding of prediction weight code (AVC-474)

Coding the field only if it changes was discussed.  It was pointed out that experimental setting should be checked against TM   Mr. Koster offered raw statistical data of the experiment results for further analysis.

The current status of spatio-temporal weighting is that it has been proved effective, particularly for the low bit rate base layer of H.261 and that switching is recommended since continuos weighting is considered costly in implementation.

However, Mr. Ueno expressed his concern about whether effectiveness of continuous weighting has sufficiently been demonstrated.  It was also pointed out that the use of continuos weighting instead of switching should be reviewed by Implementation Study group in the light of that spatio-temporal weighting is not used for bi-directionally predicted pictures, thus memory access would not be problematic

	c. Low cost version (AVC-482)

Possibility of spatial scalable scheme covering both single and double loop decoders was shown.  It was clarified that he purpose of low cost version is to meet functionalities provided by frequency scalability.

It was also stressed that switching capability in the decoder as in Figure 7/AVC-482 will allow supporting both of high Level single loop and low Level double loop configurations.

	d. Upconversion filters, H.261 compatibility (AVC-461)

Three alternative methods for specifying upconversion filters in the spatial scalable scheme were reviewed.  The meeting felt that the solution may be to define a minimum number of sets and to choose a closest one for each particular case.

Members are requested to provide specification proposals for the H.261 compatibility support assuming that spatial scalability may be the solution for this purpose (Note that system consideration is awaiting further study, see §6.4.3 of this report).  The following items are particularly noted (see AVC-366);

•	filters for CIF-CCIR601(525/60) conversion,
•	selection of corresponding lower layer pictures when picture rates are different between higher and lower layers including the case that picture skipping is involved in the lower layer, 
•	multiplexing method for the two layer signals.

	e. Application to stereoscopic coding (AVC-469)

Application of spatial scalable scheme to stereoscopic coding was presented.  During the discussion, it was clarified that application standards will define "user_data" and "disparity compensated prediction".

	f. Hooks for spatial scalability extension (AVC-470)

The meeting confirmed that necessary hooks for this and other purposes have been provided by extension_start_code and extension_id in the frozen syntax for Main Profile at main Level.

	g. Comparison between pyramidal and spatio-temporal prediction schemes (AVC-494)

Experimental results were presented indicating that the two schemes are very similar in performance at 15+20 Mbit/s and that it was very hard to distinguish the subjective difference for a "Fashion show" sequence.

There was a comment whether the results are the same for fast moving sequences as well.

	6.4.2 Frequency scalability

	a. Data partitioning (AVC-457)

Experimental results were presented for reconstructing pictures only from the base layer data, indicating that obtained pictures are very limited in quality.

Mr. Sikora clarified that possible applications of this from of frequency scalability would be FF/FR and displaying lower resolution pictures even if drift is involved.

There was some discussion on possible reasons for different values of the base layer data percentage in Table 2/AVC-457 and Table 2/AVC-472.  Difference of N values, difference of 525 line and 626 line versions of Flower Garden were mentioned.

	b. Extraction for interlaced materials (AVC-478)

Experimental results were presented with tape demonstration to show that simple field based decimation leads to a better quality extracted image.

	c. Scalable side information (AVC-489)

Experimental results for the use of SSI syntax extensions were presented.  The meeting felt that details of experimental set up need be clarified to compare the results from different organizations.  

There was a general comment that a combination of extraction in the DCT domain and decimation in the pel domain should be carefully handled.  GCT method of decoder only solution (§D.10/AVC-491b) was also noted in this regard.

	6.4.3 Comparison (AVC-467,479,486; TD-4,5,12,14)

Three contributions provided comparison study results on the two scalable schemes; spatial scalable and frequency scalable schemes.  The issue is whether we need both in the standard or there is possibility to have an integrated scheme (Note - clarification is needed whether integration is for syntax or decoder or both).  Advantages and disadvantages are compared in terms of functionality and performance.  After a general questions and answers session, Mr. Tabatabai undertook to coordinate a small group to further elaborate the comparison, to identify functionalities which are overlapping between the two, and to identify open issues.

The outcome is shown in Annex 7.  The meeting recognized that this comparison table would give a good start for another round of elaboration and agreed to adding disclaimer indicating that the comparison table is an interim summary.  It should be noted that several features may not necessarily be obtained concurrently. 

As to the scalable system configurations illustrated in TD-4 (spatial scalable) and TD-5 (frequency scalable), the following comments have been obtained;

•	Multimedia multiplexing can be also VC based (ss and fs).
•	Scalable schemes can be used for browsing database, continuous presence multipoint systems (ss and fs).
•	MCU in TD-4 may be generalized to cover B-N interworking (ss).
•	Interconnection between MCU and H.320 terminal have two possibilities; MCU having an N-ISDN interface or having a B-ISDN interface but connected through B-N interworking unit.

Chairman emphasized that we should continue system consideration for audiovisual communications; spatial scalable, frequency scalable, simulcast and switchable solutions should be fully compared in the light of overall system design.

6.5 VBR

	6.4.1 bit_rate and vbv related fields in the sequence header (AVC-452)

It was reported that the joint sessions did not accept proposals of bit rate indication and VBV extensions for VBR operation due to lack of common understanding on the necessity of such extensions in the video decoding process.

We recognized, however, that a case of data retrieval from DSM (database) which contains VBR coded data should be studied and that communication with Systems Committee is needed.

	6.4.2 UPC (AVC-447,462)

The SGXVIII response to our question indicated that UPC time constant in the range of seconds or more is not likely implemented in the network.  Since the message needs some clarification, Chairman will get contact with Mr. Coudreuse for better understanding of the message, .the second last paragraph in particular mentioning time constant relevance to the delay requirements.

The second report on leaky bucket size experiments was presented, indicating that Leaky Bucket Size does not have critical effect on encoder buffer delay for the applied coding parameter control method (VBR mode if Leaky Bucket occupancy < 90 % of Leaky Bucket Size, otherwise CBR operation).  Additionally it was mentioned that smaller leaky bucket counter size may be required if slice to slice control is used instead of the current picture to picture 

6.6 Syntax (AVC-483; TD-16)

It was clarified that most of the proposals in the contribution had been reflected in the frozen syntax (AVC-492), but with some restrictions on the combination of syntactic elements.  The new sequence layer syntax is illustrated in TD-16.

7. Network aspects

7.1 Multimedia multiplex

	7.1.1 Use of MPEG Program Stream (AVC-463)

A case study was presented for multimedia multiplexing in videoconferencing by using MPEG-1 Systems.  During the discussion, there was a comment that the current limitation of 300 packets per second for Constrained System Parameter Stream came from cheapest implementation software decoding and the value is not so scientifically grounded.  The meeting recognized that reflection of AV communication requirements to MPEG-2 Systems is urgent.

It was also pointed out that priority for the transmission of elementary data (Audio, Video, Data and Control packets) need be studied and the case study should be continued for other type of AALs with impact of different QoS use taken into account.

Chairman raised a question whether we seek the common text approach for multimedia multiplexing Recommendation as well.  Members are requested to consider this point toward the next meeting.

	7.1.2 Video clock recovery (AVC-465)

Use of network clock source was proposed for the environments that it is commonly available to the encoder and decoder.  The meeting accepted this proposal as the cell arrival time jitter is still to be buffered out in the video clock recovery method using SCR and Time Stamps.  It was concluded that placing the flag in the pack header is appropriate.

This proposal will be put forward to the Systems Committee as a proposal of the TSS Experts Group.

7.2 AAL/ATM

	7.2.1 Error correction in AAL (AVC-447,459)

SGXVIII returned to us their response on support of H.320 terminals in B-ISDN, suggesting use of FEC in AAL at bit rates not lower than 384 kbit/s.  Resilience to random bit error in the cell has been awaiting study.  AVC-459 provided an FEC scheme using Reed-Solomon code to meet these requirements.

The meeting supported this method in principle, encouraged the contributor efforts to further reduce the delay, and agreed to reach a firm conclusion in July and propose it to SG13.

	7.2.2 Relationship between MPEG-2 Systems and AAL/ATM 
	          (AVC-464,468,475; TD-15)

Three contributions addressed comparison of functionalities between transport stream and AAL/ATM.  After some questions and answers, Mr. Dunstan undertook to lead further discussion.  The outcome is contained in Annex 8.

The meeting reached common understanding that we need a good protocol reference model and reflect it to the discussion in the MPEG Systems Committee and "Adhoc group on relationships to ATM AAL".  To achieve this objective, the meeting asked Mr. Dunstan to organize drafting the model and a tutorial on AAL/ATM through correspondence with the support of Mr. D. Beaumont and Mr. T. Tanaka.

7.3 DSM CC (AVC-466)

Mr. Koster outlined and commented on the current DSM CC activities which are projected to become a part of MPEG-2 Systems standard.  The meeting noted its relevance to the terminal-to-terminal inband procedures for audiovisual communications.

8. Work plan

8.1 Network development (AVC-448)

A recent version of "IVS Baseline Document" has been received, which was approved at the January meeting of SGXVIII.  This version includes the updated list of standardization programs in relevant standardization groups such as SGXVIII, SGXV, MPEG.

8.2 Recommendations (AVC-484)

Chairman presented an updated version of "List of open issues" which reflects the achievements in the Torino/Roma meeting.  This document also includes timetable and target dates for related Recommendations and priority.

As to the common text approach for H.26X|MPEG-2, Mr. Sebestyen drew attention of the meeting to the guide for collaboration between CCITT and JTC1 which was distributed at the Torino meeting.

Chairman stressed the importance of generating not only video coding Recommendation but also total system Recommendations to allow realization of audiovisual communication systems in ATM environments.  He raised a target date of early 1995 for such Recommendations, when H.26X|MPEG-2 is expected to be approved by Study Group XV.

Though the network service provision is not yet fully clarified, the meeting felt sympathy for ideas of making necessary Recommendations before proprietary solutions appear in the market and avoiding a situation of having no terminals to connect when the network starts service.

Chairman will prepare a framework of such Recommendations for the consideration of the next meeting in July 1993.

9. Others

9.1 Intellectual property (AVC-487)

Mr. Sebestyen drew attention of the meeting to the CCITT code of practice concerning patents handling in the development of Recommendations, particularly to the point that technical proposals should be accompanied by information on any known patents or any known pending application.  

Some difficulty was expressed for disclosing "pending application", i.e. those patents not yet in the public domain, due to different patent systems in different countries.

Members are requested to follow this code of practice

9.2 Future meetings

Meeting	Date	Sole sessions	Joint sessions with MPEG	
12th	July 1993	July 7-9 in Boston	July 12-16 in New York	
13th	September 1993	two days in Brussels	September 6-10? in Brussels	
14th	November 1993	three days in Korea	November 1-5 in Seoul	

END
*    *    *

Annexes

Annex 1	Documentation
Annex 2	List of tape demonstrations
Annex 3	Report of regional coordination meeting on 28 March 1993
Annex 4	Profile architecture
Annex 5	Video buffering verifier
Annex 6	Support aspects required for "Layered" video coding algorithms
Annex 7	Comparison table for spatial scalability and frequency scalability
Annex 8	Comparison of MPEG-2 Systems and AAL/ATM

Participants of the eleventh meeting of Experts Group for ATM Video Coding 
29 March - 7 April 1993 in Sydney and Melbourne

			S	M		
						
FRG	Mr. B. Hammer	Siemens	X	X		
	Mr. I. Sebestyen	Siemens	X	X		
	Mr. G. Zedler	DBP TELEKOM	X	X	CM	
						
Australia	Mr. R. J. Arnold	Australian Defence Force Academy	X	X		
	Mr. M. Biggar	Telecom Australia	X	X	CM	
	Mr. M. Chang	Telecom Australia		X		
	Mr. M. Delahoy	Department of Transportation and Communications	X	X		
	Mr. S. Dunstan	Siemens	X	X		
	Mr. S. Hall	Monash University		X		
	Mr. A. Johnson	Telecom Australia	X	X		
	Mr. M. Leditschke	Telecom Australia	X	X		
	Mr. K. Ngan	Monash University		X		
	Mr. J. Princen	Telecom Australia	X	X		
	Mr. T. Sikora	Monash University	X	X		
	Mr. P. Stevens	Siemens 	X	X		
	Mr. T-K. Tan	Monash University	X	X		
						
Belgium	Mr. O. Poncin	Belgacom	X	X	CM	
						
Korea 	Mr. J-H. Jeon	Korea Telecom	X	X		
	Mr. J-Y. Nam	ETRI	X	X	CM	
	Mr. S-H. Park	Korea Telecom	X	X		
	Mr. H-J. Yun	ETRI	X	X		
						
USA	Mr. E. Hannah	Intel	X	X		
	Mr. B.G. Haskell	AT&T Bell Labs	X	X		
	Mr. D. Klenke	CLI	X	X		
	Mr. R. Schaphorst	DIS	X	X		
	Mr. G. Sullivan	PictureTel	X	X		
	Mr. A. Tabatabai	Tektronix	X	X	CM	
	Ms. A. Wong	Bellcore	X	X		
						
France	Mr. G. Eude	CNET	X	X		
	Mr. J. Guichard	CNET	X	X	CM	
						
Italy	Ms. L. Conte	CSELT	X	X	CM	
						
Japan	Mr. K. Hibi	Sharp	X	X		
	Mr. Y. Machida	Matsushita	X	X		
	Mr. T. Murakami	Mitsubishi	X	X		
	Mr. S. Okubo	NTT	X	X	Chairman	
	Mr. K. Sakai	Fujitsu	X	X		
	Mr. Y. Takishima	KDD	X	X	(CM)	
	Mr. T. Tanaka	NTT		X	CM	
	Mr. H. Ueno	Toshiba	X	X		
						
Netherlands	Mr. A. Koster	PTT Research	X	X	(CM)	
						
Norway	Mr. G. Bjøntegaard	NTR	X	X	(CM)	
						
UK	Mr. G. Morrison	BT	X	X	CM	
	Mr. I. Parke	BT	X	X		
						
Sweden	Ms. C. Verreth	Telia Research 	X	X	CM	

							  CM: Coordinating Member
							(CM): Substitute for CM