CCITT SGXV                                  					       Document AVC-443R
Working Party XV/1                        					       January 29, 1993
Experts Group for ATM Video Coding
(Rapporteur's Group on Part of Q.3/XV)

SOURCE:	CHAIRMAN OF THE EXPERTS GROUP FOR ATM VIDEO CODING
TITLE    :	REPORT OF THE TENTH MEETING IN TORINO AND ROMA
	(21-29 January 1993) - PART I and PART II
Purpose  :	Report

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

Part I	General
Part II	Sole sessions in Torino
Part III	Joint sessions in Roma (see AVC-444R)

Part I  General

The tenth meeting of the Experts Group was held in Italy as follows;

- 	CCITT sole sessions in Torino during 21-22 January at the kind invitation of CSELT, 
- 	Joint sessions with ISO/IEC JTC1/SC29/WG11 (MPEG) in Roma during 25-29 January at the kind invitation of the Ministry of Posts and Telecommunications.

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

Dr. Franz May announced to resign Coordinating Member of FRG due to his new mandate.  The meeting thanked his active contributions to the progress of the Experts Group and wished his success in the new environments.

Part II  Sole Sessions

Contents

1. 	Introduction
2. 	Documentation
3. 	Tape demonstration
4. 	Review of the previous meetings
5. 	Test Model
6. 	Low delay mode
7. 	Error resilience
8. 	Compatibility
9. 	Frequency scalability 
10. 	Core Profile 
11 	Work plan
12. 	Joint sessions with MPEG

1. Introduction

The CCITT sole sessions were held in the CSELT main building during 21-22 January 1993 at the kind invitation of CSELT .  At the opening session, Dr. Leonardo Chiariglione (Head, Multimedia and Video Services) made a welcoming address on behalf of the hosting organization.  

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

We had also a short closing session on January 29 at Ministero P.T. to review both sole and joint sessions as well as to prepare for the Sydney/Melbourne meeting 

2. Documentation (TD-2)

For the sole sessions, 44 AVC-numbered documents and 8 Temporary Documents have been made available as listed in Annex 1.

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 Ipswich/London meeting (AVC-398R,399R, 435)

Chairman introduced some amendments in AVC-398R which were made to reflect the review of the draft at the London closing session.  Mr. Biggar presented the outcome of the correspondence work for the multimedia multiplex summary table which were contained in a liaison statement to SGXVIII.

4.2 WPXV/1 meeting (AVC-401,402)

Chairman presented the outcome of the outcome of the WPXV/1 meeting in November 1992, highlighting items relevant to this group; 

-	general SGXV and MPEG relationship, 
-	multimedia multiplexing, 
-	common text approach for H.26X|MPEG-2, 
-	timetable for broadband audiovisual system Recommendations, 
-	PSTN videophone.

4.3 CMTT/2 and its SRG

Mr. Zedler briefly introduced current activities of CMTT/2 and its SRG and CCIR, focusing on their relationship with MPEG activities.

5. Test Model

5.1 TM3 (AVC-400, 400b)

Mr. Koster presented his editorial work for documenting agreed coding algorithm and (core) experiments.  He raised a question whether TM4 is required in the light of freezing specifications in March, and whether agreed specifications should rather be transferred to Working Draft.  The meeting felt that as far as new action points are identified, they should be documented somehow, e.g. as TM3bis.

5.2 Basic performance (AVC-420)

A part of TM2 coded HDTV pictures (reported previously in AVC-365) were demonstrated in CCIR601 format.

6. Low delay mode

6.1 Clarification on TM3 specifications (AVC-417)

The meeting reviewed proposed clarification concerning;

-	decoder operation,
-	value of the vbv_delay field to be set at the encoder and its use at the decoder, 
-	data removing timing in VBV,

and concluded as almost agreeable, but decided to leave it for further study due to limited time available for this discussion.

6.2 Special prediction

Mr. Nakajima and Mr. Bjoentegaard summarized current status of the experiments and converged simple architecture, reporting that SNR improvement obtained with this method exceeds that of bi-directional prediction (frame/field adaptive, M=3) at 4 Mbit/s if averaged over whole sequences   Position of the CCITT Experts Group was concluded as follows;

"In the interest of improving the low delay operation, many members of CCITT EG are supportive of inclusion of this technique in the core (mandatory element for the decoder, the encoder may implement it as an option), but some are not due to its increased complexity."

6.3 Non 8x8 DCT (AVC-415)

Reduction of mosquito noise by use of adaptive 8x1/8x8 DCT were demonstrated for low delay operation.  As response to a question, it was clarified that selection of 8x1 DCT is about 50%.  There was an unanswered question whether vertical 1x8 DCT also helps to reduce coding artifacts.  The meeting further discussed whether this technique is reducing the same or different redundancy with other techniques such as special prediction, frame/field DCT.  Feeling was that this technique attacks different physical property of the coding algorithm compared to special prediction and field/frame DCT (transform vs decorrelation), thus their improvements will be additive.  Related to this discussion, there was a suggestion of testing this technique for progressive sources.

7. Error resilience

7.1 Framework 

	7.1.1 Cell loss generation for experiments (AVC-421)

The meeting agreed to the modification of the cell loss generation method contained in TM3 and the warning note proposed in AVC-421.

	7.1.2 Error resilient operation of the decoder (AVC-432)

The meeting appreciated the decoder strategies for errors provided in AVC-432, confirming that this area is outside the scope of standardization.

	7.1.3 Informative text for H.26X|MPEG-2 (AVC-425; TD-7)

Error resilience techniques and how to use them in error prone environments are to be included in the standard as informative text.  Mr. Bigger provided a draft framework in AVC-425 containing list of contents and information required and Mr. Sakai provided a summary of cell loss resilience schemes to make this text further informative.  Mr. Biggar coordinated a small group discussion to draft a text to be included in WD and generated an expanded framework as in Annex 3.

During this discussion, it was reminded that protection against bit errors in ATM cells is awaiting study.

	7.1.4 Relevance to "Core Profile" (AVC-426)

Document AVC-426 proposed to consider that an error resilience method with scalable extension be considered for the MPEG-2 core because not only it can achieve cell loss resilience but also scalability functionality with minimum complexity, the core should be as big as possible.  There was some strong support for this proposal, but different views were also expressed that its resilience performance is not yet fully demonstrated, that spatial scalability similarly provides cell loss resilience and that including too much in the "core profile" may not bring expected wide availability of standards conforming products.  It was also argued that "core profile" is yet to be well defined.

The meeting concluded that no consensus of the group was obtained, thus this proposal be forwarded to the joint sessions as an individual input.

	7.1.5 Cell loss characteristics for VBR video (AVC-430)

Document AVC-430 provided simulation results for average burst length and average inter burst length by using modeled VBR MPEG-1 video traffic.  There was a comment that the average burst length is for multiplexed sources, thus each source would suffer only 1/N of the value listed in Table 1/AVC-430.  Another comment was a request to relate this model for calculating CLR and the network model being used in this group (see Annex 4 to AVC-357).

As to the use of 10*N cells buffer, concern was expressed for increased delay.  It was responded that this study was carried out for multiple program transmission for satellite and delay is not so critical in satellite distribution systems.

7.2 Concealment (AVC-405; AVC-403,407,412,432)

Error concealment by use of motion vectors in I-frames was presented in AVC-405.  In response to a question whether inclusion of motion vectors to intra macroblocks increases error resilience, Mr. Uz clarified that for an intra macroblock a motion vector is available at the inter macroblock above it. thus the improvement is small.  He also clarified that if the encoder does not wish to send motion vectors for I-pictures, it can do so without losing coding efficiency by not using the particular picture macroblock_type table entry.  There was another question of what would happen if the motion vector above the lost macroblock is also lost and the answer was to use the motion vector of a further above macroblock.

The meeting concluded that further study is required in comparison with other alternative techniques.

7.3 Spatial localization (AVC-406,412,427,428; AVC-403)

Documents AVC-406,412,427,428 addressed;

-	structured packing vs short slice size,
-	structured packing and/or concealment,
-	AAL and video syntax specifications to support the structured packing.

The meeting concluded that CCITT EG does not support the inclusion of "absolute macroblock" for error resilience purpose because the short slice method can achieve similar performance without changing the syntax.  However, use of this structured packing technique at the system level is open.

During the discussion, error resilience study for transmission of pre-recorded materials and cascading two transport methods, e.g. satellite and ATM, was pointed out.  Ms. Verreth suggested from her observation (see AVC-432) that applying different slice sizes for I, P, B pictures may be effective.

7.4 Temporal localization - leaky prediction (AVC-403,413,414,431,442; TD-4; AVC-412)

Several experimental results were reported on leaky prediction giving the following findings;

-	Two solutions for the limit cycle fix offer the similar performance.  A small difference is that Solution 2 gives perfect tracking between encoder and decoder while some residual (-50 dB) remains in Solution 1.

-	As to the noisy background, AVC-414 showed that adaptive quantization of dc components solves the problem.  This fact corresponds to the results demonstrated in AVC-413; leaky prediction using rate control of up to Step 2 showed significant noisy background but it disappears in non-leaky prediction of dc components.

There was a question how this technique affects random access and editing with an answer that it allows random access by starting to decode one or two seconds in advance, but does not group of picture editing.  It was also pointed out that picture unit editing, which is required in program production, is only possible with wholly intra coding.

As to channel hopping performance, Mr. Haskell suggested compensating leak factor at the decoder to improve performance.

There was a general comment to the leaky prediction that there is inconsistency of design philosophy in seeking high prediction efficiency by special prediction on one hand and losing it by leaky prediction on the other hand.

The meeting concluded as follows;

CCITT EG supports the cyclic INTRA insertion (INTRA picture, slice, column) as a default solution for temporal localization of cell loss affects and for channel hopping.  However, a final decision will be made after one more round of experiments to compare these two solutions.

7.5 Layered coding (AVC-404,407,424)

The following three error resilience techniques by layering were presented;

-	coefficient scanning(AVC-404)
-	spatial scalability (AVC-407)
-	frequency scalability (AVC-424)

They all assume a guaranteed channel for high priority (base layer) and are most effective at cell loss rates of 10-3 or higher.  During the discussion, the following clarification or comments were stated;

-	In  the coefficient scanning, reproduction of HP components only gives blurring and jerky pictures if 25% is assigned to these components.  Coding efficiency is not lost if there is no rate control in the base layer; rate control for 25% assignment case is most difficult.
-	Frequency scalable scheme achieves layered coding with minimum increase of complexity.
-	A difference between spatial scalability and frequency scalability is that the former supports compatibility.  The same base layer performance is obtained with less bit rates in the spatial scalability.  If anything can be done in the coefficient domain, it must be achievable in the pel domain as well.

The meeting concluded that this topic requires further study together with the issue how to structure scalability functionality in the standard.

8. Compatibility

8.1 Framework (AVC-409,419,440,441; AVC-416)

Documents AVC-409 and 419 addressed;

-	system consideration; where this "compatibility" is effective in terms of communication situations and bit rates,
-	flexible layering.

To the embedded architecture raised in AVC-409, there was a question whether 25% more throughput increase leads the standard to the widest use.  A rebuttal is that the cost problem will go away in the future, starting with a little more cost will facilitate the future.  Another question was whether flexible layering eventually requires full layering to achieve interworking among different applications.  An answer was that the necessary number of layers depend on applications.

Document AVC-419 provided discussion materials for a particular case of multipoint communication system, pointing out some items requiring further input.  Mr. Biggar commented that H.32X-H.320 interworking is transitional, thus we should focus on long term solutions looking at the time when B-ISDN prevails, but some others expressed a differing view that the interworking requirement would last for a considerably long transitional time.  

Similar system study for frequency scalable scheme and comparison with spatial scalable scheme is requested as pointed out in §6.4.3/AVC-398R (Ipswich/London meeting report).  These two may be alternatives or may have their own areas.

Document AVC-440 analyzed approaches to the upsampling filter of the compatible scheme for discussion.  Consideration of the members is requested.

Document AVC-441 proposed some items to exploit the correlation between similar video signals over a pair of video codecs (such as stereoscopic coding).  As to the interlace/progressive indication, the meeting considered that it should be in picture layer rather than sequence layer, taking into account other requirements of rapidly switching between progressive film sources, interlaced camera sources, etc. as well (see also §5.3/AVC-398R).  As Items 2 and 3 received reservation, the meeting concluded that this proposal be forwarded to the joint sessions as an individual input.

8.2 Interlace-progressive compatibility (AVC-422; AVC-411)

Document AVC-422 informed that adding compatible prediction to even fields from the odd field base layer does not affect performance in SNR and subjective quality in a field picture compatible scheme.  A possible reason is temporal misalignment between predicting and target pictures.  Mr. Ueno commented that in frame picture structure prediction from base layer picture improves coding efficiency of I frames of the target regardless of the temporal misalignment.

8.3 Interlace-interlace compatibility (AVC-408,411,423,433,434)

Documents AVC-408,411,433 reported coding results of the spatio-temporal weighting for the interlace-interlace compatibility scheme.  AVC-412 showed coding loss of the compatible coding in a sequence, to which a suggestion was given to visually check prediction errors if there is any pel displacement; pel displacement appears as disturbing moire-like patters.

There was some discussion on requirements to upsampling and downsampling filters for the compatible coding.  It seems that filters appropriate for obtaining best efficiency in the enhancement layer and those for obtaining best pictures in the base layer are not the same.  For prediction, pel alignment is critical to usefulness of the base layer.  As to complexity of the compatible scheme, Mr. Morrison pointed out a possibility to use reordering memories for up/down sampling filters.  AVC-423 reported relevant experimental results regarding horizontal upsampling filters, informing that tried simple and complex filters did not differ in coding efficiency.

There was also a comment that relationship between complexity of downsampling filters and coding efficiency is also studied in frequency scalable coding, hence the results should be compared.  Mr. Parke drew attention of the meeting that coding efficiency of the compatible coding is quite sequence dependent.

Differing views were expressed regarding spatio-temporal weighting; some thought it is not justified for adoption, others thought it is effective.  The meeting concluded that study should be continued.

Document AVC-433 reported on HDTV/CTV compatibility experiments using pyramid coding.  Mr. Nam stated his observation that 4:2:2 and 4:2:0 in HDTV show no significant difference.  There were comments that this pyramid scheme had been tried previously for compatible coding but now it evolved into the current spatial scalable scheme.

8.4 H.261 compatibility (AVC-416,429,439)

Document AVC-416 reported on cascade coding of MPEG-2 at 4 Mbit/s and H.261 at 1.5 Mbit/s, 384 kbit/s and 128 kbit/s indicating that this is one of the possibilities to make a compatible system.  Concern was expressed for increase of delay, leading to that this technique is applicable when two bit rates are largely different.

The other two documents AVC-429 and 439 addressed embedded coding, demonstrating spatio-temporal weighting is effective for H.261 in the base layer.  An interpretation is that low bit rate H.261 pictures are not so good as 1.5 Mbit/s MPEG-1 base layer pictures.  To the block noise observed in the non-compatible scheme of AVC-429, a possibility of actual motion exceeding the motion vector tracking range was pointed out.  Characteristics of up/down sampling filters to obtain better coding efficiency and better H.261 layer pictures are subject to further study as in §8.3.

8.5 SNR scalability (AVC-410)

Two SNR scalable configurations were tested in AVC-410 according to the compatibility/spatial scalability syntax.  In response to a question that coding efficiency could be further improved, Mr. Parke clarified that removing current overhead in the enhancement layer video multiplex coding will bring improvements.

As to possible applications of this SNR scalability, broadcasting and data base were listed as typical ones.  Another possibility of software decoder in computers was also mentioned.

9. Frequency scalability (AVC-424,426)

The meeting shortly considered where this functionality is most effective.  The following three areas were found typical;

	-	computer networks,
	-	in processing power sensitive areas rather than in bit rate sensitive areas,
	-	in broadcasting situations.

10. Core Profile (AVC-418,438)

The meeting discussed what definition is desirable from communication applications consideration.  Though common understanding on "core" definition is not yet obtained, Chairman stressed in response to the questions in AVC-438 that current efforts in the generic coding framework are not to define application oriented profiles (such as telecom profile, broadcasting profile, ...), but functionality oriented profiles.  It was also stated that "profile" is closely related to conformance.

Document AVC-418 proposed attributes and their values of the core profile in terms of TM3 syntax elements, taking five typical audiovisual communication services on B-ISDN into account.

Two differing views were expressed for the core profile;

-	It should include maximum number of functionalities necessary for communications to achieve interworking.
-	It should be practical in functionality to make commercial production take off.  It should be really minimum but still useful.

Since no consensus on the proposal contained in AVC-418, the meeting confirmed that this should be provided as a discussion paper for consideration of the joint sessions.

During the discussion, Mr. Stevens suggested to evaluate implementability of each functionality listed to decide practicality of the core.  Mr. Parke drew attention of the group that H.26X|MPEG-2 should support not only 4 Mbit/s or above, but also lower bit rates down to 64 kbit/s to support various scale pictures.  

As a further step, this group should study relation between H.26X|MPEG-2 profiles (core and extension) and total system Recommendations.

At the closing session in Roma, the meeting confirmed that we need not a separate "low delay profile", rather we need a low delay operational mode contained in the "Main Profile" (Note)  so that we can achieve service integration at the B-ISDN terminal.  It should be checked that all the necessary syntactic elements for low delay operation are included in "Main Profile"; skipped picture, special prediction, VBV consideration, and others if any.  It was also recognized that there may be defined another profile which addresses no B pictures thus allows low delay, but its objective is low cost, hence it should not be confused with the above mentioned "low delay profile".

	Note - A profile previously called "Core Profile" was renamed as "Main Profile" at the joint sessions in Roma.

11 Work plan (AVC-402,436,437; TD-5)

Document AVC-436 provided work items, their current status, timetable, etc. for consideration of the group.  TD-5 is an excerpt from the document "GUIDE FOR CCITT AND ISO/IEC JTC1 COOPERATION" to highlight the synchronization of H.26X|MPEG-2 approval process between two standardization bodies.

The target dates for total system Recommendations and priority should be more clearly stated at the next meeting.  In the mean time, Chairman of Experts Group will seek advice of Chairman of Working Party/1 and Special Rapporteur of Q.4/XV from the overall SGXV planning perspective.

As to the H.320 terminal adaptation proposed in AVC-437, the meeting agreed to its inclusion in the Experts Group work program based on the understanding that this has already been studied to some extent in the B-N interworking framework and that the Group's terms of reference include "to study video coding algorithm appropriate to the ATM environment for conversational services, particularly to study whether modifications are necessary to make the present AV Recommendations applicable to the ATM network".

12. Joint sessions with MPEG

12.1 Documents

Information and discussion documents

AVC-403,404,405,406,407,408,409,410,411,412,413,414,415,416,417,418,420,422,423,424,
427,428,429,430,431,432,433,434,438,439,442

Individual proposal documents

AVC-426,441

Group proposal documents

AVC-412,421,425; TD-7

12.2 Representatives

	CCITT EG			S. Okubo
	Requirements 		A. Tabatabai
	Video				G. Bjoentegaard
	System			B. Haskell
	Implementation		P. Stevens

13. Others

Future meetings

	March/April 1993	joint sessions in Sydney (March 29 - April 2)
				sole sessions in Melbourne (April 5-7)

	July 1993		sole sessions in ???
				joint sessions in New York (July 12-16)

	November 1993 	sole sessions in ???
				joint sessions in Seoul (November 1-5)

At the closing session in Roma, it was agreed that we will have a coordination meeting among regional coordinators (America, Asia, Europe, Oceania) during 16:00 - 18:00 on Sunday, March 28 to prepare for the joint sessions which are held before the sole sessions this time.  Chairman will later advise Group members of the details.

END

*    *    *

Annexes

    Annex 1	Documentation
    Annex 2	List of tape demonstrations
    Annex 3	Error resilience framework for informative text and further experimentation

Participants of the tenth meeting of
Experts Group for ATM Video Coding 
(21-29 January 1993, Torino and Roma)

			T	R		
						
FRG	Mr. M. Kühn	DBP TELEKOM		X		
	Mr. F. May	Daimler-Benz	X		CM	
	Mr. G. Zedler	DBP TELEKOM		X	CM	
						
Australia	Mr. M. Biggar	Telecom Australia	X	X	CM	
	Mr. R. Brandis	Australian Defence Force Academy	X	X		
	Mr. T. Sikora	Monash University	X	X		
	Mr. G. Smith	Optus Communications	X	X		
	Mr. P. Stevens	Siemens 	X	X		
						
Belgium	Mr. O. Poncin	Belgacom	X	X	CM	
						
Korea 	Mr. J-Y. Nam	ETRI	X	X	CM	
						
USA	Mr. B.G. Haskell	AT&T Bell Labs	X	X		
	Mr. D. Klenke	CLI	X	X		
	Mr. A. Tabatabai	Tektronix	X	X	CM	
	Mr. M. Uz	DSRC	X	X		
	Ms. A. Wong	Bellcore	X	X		
						
France	Mr. G. Eude	CNET	X	X		
	Mr. J. Guichard	CNET	X		CM	
						
Italy	Ms. L. Conte	CSELT	X	X	CM	
						
Japan	Mr. Y. Machida	Matsushita	X	X		
	Mr. K. Matsuzaki	Mitsubishi	X	X		
	Mr. Y. Nakajima	KDD	X	X	(CM)	
	Mr. S. Okubo	NTT	X	X	Chairman	
	Mr. K. Sakai	Fujitsu	X	X		
	Mr. H. Ueno	Toshiba	X	X		
						
Netherlands	Mr. A. Koster	PTT Research	X	X	(CM)	
	Mr. R. ter Horst	PTT Research		X		
						
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