ITU Telecommunication Standardization Sector	Document AVC-553R
Study Group 15	July 16, 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 TWELFTH MEETING IN BOSTON AND NEW YORK (July 7-16, 1993) - Part I and Part II	
Purpose:	Report	

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

Part I	General
Part II	Sole sessions in Boston
Part III	Joint sessions in New York (see AVC-554R)

Part I  General

The twelfth meeting of the Experts Group was held in the US as follows;

- 	ITU-TS sole sessions in Boston during 7-9 July at the kind invitation of PictureTel, 
- 	Joint sessions with ISO/IEC JTC1/SC29/WG11 (MPEG) in New York during 12-16 July at the kind invitation of Columbia University.

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

Part II  Sole Sessions

Contents

1. 	Introduction
2. 	Documentation
3. 	Tape demonstration
4. 	Review of the previous meetings
5. 	Video Source coding
6. 	Network aspects
7. 	Intellectual property
8. 	Work plan
9. 	Joint sessions with MPEG in New York
10.	Others

1. Introduction

The ITU-TS sole sessions were held at The Colonial Hilton and Resort during 7-9 July 1993 at the kind invitation of PictureTel.  At the opening session, Dr. Norman Gaut, President & CEO, 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 16 July at Columbia University to review both sole and joint sessions as well as to prepare for the Brussels meeting.

2. Documentation (TD-2)

For the sole sessions, 57 AVC-numbered documents and 12 Temporary Documents have been made available as listed in Annex 1.

3. Tape demonstration (TD-3)

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

4. Review of the previous meetings 

4.1 Sydney/Melbourne meeting (AVC-496R)

Chairman briefly presented the outcome of the previous joint and sole sessions in Sydney and Melbourne and reported progress made after the meeting on the following outstanding issues (§ numbers refer to AVC-496R);

•	VBV specifications (§6.2.2)
•	WD informative text on error resilience (§6.3.5)
•	Input of the clock recovery document to the Systems adhoc group meeting (§7.1.2)
•	Relationship between MPEG-2 Systems and AAL/ATM (§7.2.2)

The following is yet to see more actions;

•	Liaison with SG13 on UPC (§6.4.2)
•	Framework for Recommendations (§8.2)

4.2 SG15 Rapporteur's meeting in Tokyo (AVC-498,499) <AVC-500,501>

Chairman reported on the following items which are relevant to the Experts Group activities;

•	Consideration of MPEG-2 multimedia multiplex schemes for broadband applications
•	Time schedule for system aspects Recommendations
•	Protocols for desktop videoconferencing
•	Video mixing for 4xQCIF

These have been elaborated in the current Experts Group meeting.

4.3 ITU-TS SG15 Chairman, Vice-Chairmen and proposed WP Chairmen

It was reported that Mr. M. Yamashita will continue to chair WP 1/15 and cover audiovisual matters including high quality audio coding.

4.4 Systems Adhoc group meetings in Atlanta and Amsterdam (AVC-502)

Ms. J. Vollbrecht summarized the progress made in the two adhoc group meetings of the MPEG Systems which led to the update of Working Draft, focusing on such items as source clock recovery, mapping of the TS packet on AAL.

4.4 CMTT/2 and its SRG

Mr. Zedler and Mr. Poncin gave some information on the current activities of the SRG and its relevance to the H.26X|MPEG-2 activities.

5. Video Source coding

5.1 Main Profile at Main Level (AVC-503,546) <AVC-539,540,541>

AVC-503 reported basic open loop performance of the MP@ML coding scheme for M=1 in statistics and picture quality.  This is for conversational services, pending M=3 performance for distributive services to be demonstrated in New York.

AVC-546 pointed out some missing information and inconsistencies in TM5, MPEG2 Working Draft.  Questions to clarify the MP@ML syntax and semantics were left to the consideration in New York.

During discussion, it was raised whether MP@ML decoders should handle bitstreams of higher Profile/Level bitstreams.  Our conclusion was that the standard does not require it and that it is left to implementation.

5.2 Low delay mode

	5.2.1 VBV specifications (TD-4; AVC-514,519)

The Experts Group produced a proposed revision for the VBV specifications (Annex C to the WD) through correspondence after the Sydney/Melbourne meeting as contained in Annex 3.  Mr. Bjoentegaard coordinated this correspondence work.  The remaining issues are handling of the 3:2 pulldown operation and the time stamps for "large picture" as addressed in AVC-519 and AVC-514, respectively.

After some discussion the meeting decided to put forward these proposals for consideration of the New York sessions to make a choice for number_of_field_display code between "last picture removed from the buffer" and "picture to be removed from the buffer".  It also decided to propose to increment PTS and DTS by one picture time period if data is incomplete at the time it is to be removed from the buffer.

	5.2.2 Concatenation of segments with different M values (AVC-520)

AVC-520 raised a question of how to maintain the low delay characteristics when coding segments with different M values are concatenated.  We obtained a common understanding that use of the end of sequence or the AVC-520 method is an encoder option to prevent VBV violation.

The issue of low delay mode indication was revisited to facilitate maintaining the low delay operation for mixture of different M value segments.  The meeting concluded that the low delay operation is to be managed by means of PTS rather than by flagging in the video stream.

	5.2.3 Low delay possibility for M larger than 1 (AVC-523)

AVC-523 provided experimental results to achieve low delay by utilizing periodical nature of the VBR coded bit generation in IPB structures.  The meeting decided to send a liaison to SG13 inviting comments on possible network overloading even if each traffic conforms to UPC as indicated in this contribution.

The meeting also confirmed the definition of field structure M=2 as illustrated on p. 2/AVC-523.  As a result, the current TM5 description ruling out field structure M=2 for low delay should be revised (see also §6.2.2/AVC-496R).

5.3 Error resilience

	5.3.1 Concealment (AVC-532,549)

AVC-532 provided information on characteristics of basic concealment techniques.  It was clarified that in this experiment data after an error is discarded until a next start code.  Mr. Haskell pointed out that error can be detected by the decoder only some time after errored data is input.

Impacts of loss of higher level header information such as picture type, f_code and quantizer matrices were experimented and discussed in AVC-548 and 549.  Loss of the picture type and f_code is serious, while loss of the quantizer matrices slightly degrades quality.  Mr. Uz stated that redundant data is being proposed to be in the Systems TS packet.  If H.32X terminals utilize PES, one possibility to convey these redundant data is to use private data.

	5.3.2 AC-leaky prediction (AVC-515,530,531,537; TD-9)

AVC-531 and 537 provided experimental results on AC-leaky prediction presenting statistics and coded pictures, while AVC-536 proposed clean-up for syntax and semantics.  During the questions and answers, it was clarified that limit cycle is not visible in the AC-leaky prediction, thus its fix is not necessary.  It was also reminded that the current cell loss experiments are based on the lost cell being informed by the network to the decoder.

There were two input documents from Japan and Europe (AVC-515 and 530) stating that AC-leaky prediction is not necessary in the standards on the grounds that existing techniques can provide similar performance.

After having reviewed relevant papers and demonstration tapes, the meeting discussed what should be the position of the ITU-TS Experts Group on this matter.  As part of this task, comparison between AC-leaky prediction and Intra Slice was tabulated with respect to the following items as in Annex 4;

•	Coding efficiency/picture quality,
•	Cell loss resilience,
•	Channel hopping,
•	Additional hardware complexity.

Since there were split views as to the inclusion of this technique in the standard, the meeting decided to await the review of other relevant inputs in New York and evaluation there.

	5.3.3 Data partitioning (AVC-504)

Experimental results were reported for its error resilience improvements compared to the single layer coding scheme.  It was clarified that H+L is constant while H/L varies in this experiment.  Processed pictures were announced to be seen in New York.

	5.3.4 WD informative text (AVC-511)

Mr. Biggar presented the current status of the error resilience informative text.  Suggestions were made to include a general disclaimer for "D.3.1 Layered coding" taking into account the standardization work phase and to produce appropriate wording for the relationship between data partitioning and subband.

5.4 Scalability

	5.4.1 Spatial scalability (AVC-505,518,529,533,534,539,540,541,542,543,544,545; 
					TD-12)

	1) Experimental results for coding efficiency/picture quality

AVC-518, 533, 542, 543, 544 and 545 provided experimental results for SIF/CIF and 601 scalable schemes.  During the discussion, the following clarifications were made;

•	In AVC-518, macroblock type decision is based on unweighted MSE, not biased to spatial compatible.  AVC-545, however, is based on biased decision.
•	BT is experimenting with macroblock type decision taking into account chroma components as well.
•	AVC-533 suggests that H.261 compatibility should be achieved by "switchable" for point-to-point and by "transcoding" for multipoint.
•	AVC-542 proposes that continuous weighting (coefficient downloading at macroblock level) be not included in the standard due to its hardware cost penalty .
•	Experiments are encouraged to verify the approach to allow upsampling filter mismatch between encoder and decoder which is proposed in AVC-543.  There was a comment that masking effects may be reducing the visual impairments if filter mismatch does not affect the performance.

Differed views have been expressed on adoption of the spatio-temporal weighting.  There was no firm evidence to promote it or to drop it, partly because of different experimental set-up.  The meeting concluded to provisionally retain it assuming that it requires no significant addition of hardware and that there is prospect of future improvements.

AVC-505 and 534 provided experimental results for CTV and HDTV scalable schemes; particularly spatio-temporal prediction is compared with pyramidal DCT in AVC-534.  The following was clarified;

•	Both layers are 4:3 in AVC-505, while they are 16:9 in AVC-534.
•	Hardware consideration lead to M=1 for HDTV in the experiment of AVC-505.
•	In AVC-534, 12 Mbit/s has been selected for the CTV base layer taking into account high quality digital satellite broadcasting.  It is noted that the picture format is 16:9 and 4:2:2 here.

The meeting concluded that we can proceed with the current spatial scalability approach.

	2) Clean-up of syntax and semantics

AVC-541 proposed clean-up of the picture layer syntax while AVC-518, 539, 540, 541 and 546 proposed that of the macroblock layer syntax addressing skipped macroblocks, VLC for macroblock type, prediction of motion vector, SNR scalability.  During the discussion, the following was pointed out;

•	Pel location relationship between the base layer and the upper layer pictures should be specified; co-located or shifted.
•	Combination of Dual-Prime and averaging mode should be excluded from macroblock_type VLCs due to the memory bandwidth constraint.

There were some discrepancies in proposed solutions for the identified problems.  Mr. Tabatabai attempted to sort them out in a small group.  The outcome is contained in Annex 5.

	3) Upconversion filters (AVC-541,543)

AVC-541 proposed specifications of spatial scalable upsampling based on the idea that complete matching of upsampling filter is not required as experimented in AVC-543.  The meeting recognized that clarification is needed whether the encoder upsampling filter is specified as bilinear interpolation and leaving design freedom to the decoder upsampling filter or the other way around.

	4) Necessary resources for supporting spatio-temporal weighting (AVC-529)

Spatio-temporal weighting requires higher memory bandwidth, but if B frames are incorporated, the resource for that purpose can also be used for spatio-temporal weighting in I and P pictures.  It should be noted, however, that hardware does not increase only if the higher layer has B pictures. 

	5.4.2 Frequency scalability (AVC-510)

AVC-510 provided experimental results for the use of Frequency Scalability to achieve FF/FR functionality.  It has been noted that the use of base layer for FF/FR can be common to fscalable, sscalable and data partitioning.

	5.4.3 General (AVC-517,527)

AVC-527 provided information on software decoding.  The intention of submission was clarified as being a rebuttal to the argument that frequency scalability is suited for software decoding by use of small size IDCTs.  It was also pointed out that the IDCT in the attached paper uses short-cut and is not conforming to the IDCT specifications in the standards and that fscalable with small size IDCTs may not give good picture quality either.

Examples of scalability applications were discussed in AVC-517.  The following comments were given during the discussion;

•	Different colorimetries in HDTV and CTV will affect coding efficiency of the sscalable scheme.  It may be more difficult to cope with this in the fscalable scheme.
•	4:2:2 extension in fscalable is not clear.

5.5 VBR and its delay (AVC-522)

AVC-522 provided experimental results for the two methods to give upper bound for the octet interleaving delay for the VBR coded video; to keep a minimum bitrate and to set a time-out for flushing the interleaver matrix.  It has been shown that some strict UPC methods can assure a certain maximum delay for VBR coding even if interleaving is involved.  There was a comment that a method to turn on/off interleaving according to the bit rate may help though its practicality is to be checked.

5.6 Specific video techniques

	5.6.1 Object oriented coding/decoding (AVC-509)

A proposal was made to allow encoding/decoding objects separately each of which consists of slices with identical identification.  The meeting supported the idea of including slice_id, leaving the syntax representation to further consideration.

	5.6.2 Video mixing for continuous presence multipoint systems (AVC-500,501)

This discussion is in response to the request of the Tokyo Rapporteur's meeting.  We briefly reviewed the input documents and obtained the following comments;

•	Technical feasibility should be examined in the light of overall system configuration.  Existing terminals should be accommodated without modification as far as possible.
•	Comparison should be made against transcoding MCU in terms of picture quality, delay and other factors as listed in AVC-501.

The meeting decided to continue the study toward the next meeting and the SG15 meeting (both in September) through correspondence.  Mr. Schinkel undertook to coordinate this work with participation of Bellcore, BT Labs, CNET, NTT Labs; other members are also welcome.  The task is to draft a reply to WP15/1 with respect to video coding techniques which are necessary for terminals and MCU to constitute the video mixing multipoint system.

5.7 Profiles other than Main (AVC-516,525,526,528)

Requirements for the profiles from audiovisual communication applications were discussed in the four input documents.  The following comments and clarifications were made during the discussion;

•	An opposing view was expressed to AVC-516 that H.26X/H.261 compatibility can be covered by switchable terminal and transcoding MCU, thus spatial scalability is not required for this purpose (the same view is also in AVC-533), and that cell loss resilience can be provided by data partitioning with less complex hardware.
•	Cell loss resilience may better be provided by FEC if 10% increase in bit rate is justified.
•	The question is what profile of H.26X we specify for the H.32X terminal.
•	Some of the telecommunication requirements listed in AVC-525 should be covered by H.32X, not by H.26X.  The worst case CLR of 10-2 mentioned in this document corresponds to the Australian study (see AVC-296 submitted to the New Jersey meeting).
•	SCIF listed in AVC-526 is for illustrating high quality videoconferencing.
•	AVC-528 provides high level scenarios whose implications should be studied for designing the system components such as MCU.

The meeting concluded that the discussions here are to be reflected in the Requirements sub-group work in New York.

6. Network aspects

6.1 B-ISDN characteristics (AVC-508)

Mr. Dunstan gave an overview of B-ISDN to form a common basis among the participants.  AVC-508 was intended for presentation at the Systems meeting in the joint sessions.

6.2 AAL Type 1 (AVC-521,538; TD-10)

AVC-521 and 538 addressed error correction in AAL.  The backgrounds are that SG13's response on support of H.320 terminals in B-ISDN indicated necessity of cell loss correction (see AVC-447) and that requirements from CMTT/3 on high quality sound transmission indicate the same solution for cell loss (see Annex to AVC-538).  Another factor is that we need some bit error correction mechanism as well in video signal transport through ATM networks.

There was a comment that error resilience evaluation is needed between 
-	loading the network with pure video, and 
-	use of FEC resulting in 10% more network loading, thus higher cell loss probability
assuming the same pure video bit rate.

Both AVC-521 and 538 propose solutions for the cell loss correction with low delay.  Mr. Asai and Mr. Eude collaborated to compare the two methods.  The outcome is contained in Annex 6 which is a summary of the discussion with an accompanying liaison statement to SG13.  The liaison statement was sent to Geneva where SG13 was meeting concurrently with our group.

Joint meeting with SG13 experts on AAL Type 1 and Type 2 for audiovisual communications has been suggested by Mr. Yamazaki, Rapporteur for AAL Type 1/2 in SG13.   The meeting supported this idea, awaiting detailed arrangements to be settled between the two groups.

6.3 Multimedia multiplex and AAL/ATM (AVC-498,499,506,507,524,547,550; TD-6,8)

	6.3.1 Relationship between MPEG Systems and AAL/ATM

AVC-507 listed functionalities for supporting the audiovisual communication services to answer a question of what are required for video support AAL without considering MPEG Systems.  The following was listed as a conclusion of the discussion;

•	Transfer of variable length data units.  Interval between data units may be fixed or variable.
•	Multiplexing and synchronization of elementary streams
•	Capability to synchronize source and receiver clocks 
•	Error detection capability

AVC-498, 499 and 506 discussed use of all or part of MPEG Systems as a possible multimedia multiplex method for audiovisual communication applications.  Alignment between ITU-TS Recommendation and ISO/IEC standard is also an issue.

The meeting concluded that technical solutions should first be established and the alignment should be clarified based on the technical solutions.

AVC-507, 524, 547 and 550 discussed interaction between MPEG Systems and AAL/ATM listing possible scenarios to find optimum solutions both for H.22X in the H.32X terminal and for transfer of TS packets over B-ISDN.

After general review of these contributions, Mr. Dunstan coordinated a night session for detailed analysis.  The outcome is contained in Annex 7.  Contributions are requested toward making a choice out of the listed alternatives.

	6.3.2 Independent clock sources and their recovery at the decoding end (TD-7)

There can be several independent clock sources in the audiovisual terminal.  They should be identified and the recovery method for each source should be clarified.  This is yet to be worked out for the H.32X terminal.

6.4 Audiovisual protocols for LAN (AVC-498,512,513)

AVC-498 and 512 discussed features of audiovisual communication systems over LAN, while AVC-513 discussed necessary functionalities of multimedia multiplexing in particular.

Several participants expressed prompt interests in standardization of this area.  The meeting concluded that this Experts Group should draft necessary Recommendations and that time frame should be set for this work, seeking advice of WP15/1 as well.

Contributions are solicited.

7. Intellectual property (AVC-551)

AVC-551 proposed the following regarding the H.26X related patents;

•	Disclosure of patent information relevant to technical proposals
•	Adoption of waiving patent rights (at least for ITU applications)

As to the second point addressing the ITU applications, a view was expressed that different policies should not be taken between telecommunication and information technology standardization bodies.

The meeting concluded that "disclosure of patent information" should immediately be followed to conform to the ITU-TS code of practice and that the second point should be advised to and consulted with patent experts in each participating organization.

8. Work plan (AVC-499; TD-5)

We confirmed that the Tokyo Rapporteur's meeting had supported to set a target of early 1995 for "minimum system" Rec. to deter from prior divergence; also to show "committee draft" on the plan (May 1994?) to focus attention on preparation of first solid draft.  Here "minimum system" is meant to be a minimum total audiovisual communication system (H.32X) consisting of video/audio coding, multimedia multiplex, communication procedures, etc.

Chairman reminded members of hardware verification trials which should take place in the final stage of standardization work to secure our Recommendations.  Since video coding/decoding specifications will be verified mostly through the bitstream exchange currently ongoing, our task is to test the above mentioned minimum system between two or more independently designed equipment.  The date could be sometime during 1995.  Interested organizations are requested to express willingness of participation and to contribute to materializing the plan.  This topic will be part of the agenda at the next meeting in Brussels.

9. Joint sessions with MPEG in New York

9.1 Documents

The Experts Group submitted TD-4 (Annex 3 to this report, MPEG93/699), TD-8 (Annex 7, MPEG93/698) and TD-9 (Annex 4, MPEG93/700) as outcome of the sole sessions.  Other individual inputs are indicated with MPEG document numbers in Annex 1.

9.2 Representatives

The following members acted as representatives of the ITU-TS Experts Group to reflect the group's concern and report the outcome of the joint sessions.

ITU-TS EG	S. Okubo	
Requirements 	B. Haskell	
Video	G. Bjoentegaard	
Systems	S. Dunstan	
Implementation	G. Morrison	

10. Others

10.1 Future meetings

Meeting	Date	Sole sessions	Joint sessions with MPEG	
13th	September 1993	September 2-3 in Brussels	September 6-10 in Brussels	
14th	November 1993	October 27-29 in Daejeon
(See AVC-535)	November 1-5 in Seoul	

10.2 Miscellaneous

In order to compensate the discussion time shortage at meetings, Chairman encouraged the members to review the already available AVC-numbered documents when they produce new contributions, indicating AVC-number, source, title and date of referred documents at the end of each contribution.

Collection of TD-2 of the previous meetings will be distributed as an electronic file for this purpose.

END

*    *    *

Annexes

Annex 1	Documentation	
Annex 2	List of tape demonstrations	
Annex 3	Proposed text for WD Annex C - Video Buffer Verifier	
Annex 4	Summary of the discussion on AC-leaky prediction	
Annex 5	Report of the small group work to sort out the discrepancies in proposed solutions for the spatial scalable syntax	
Annex 6	Cell loss correction method for AAL Type 1 to support H.320 terminals in B-ISDN	
Annex 7	Report of discussion on ATM/AAL and MPEG-2 Systems	

Participants of the twelfth meeting of Experts Group for ATM Video Coding 
7-16 July 1993 in Boston and New York

			B	N		
						
FRG	Mr. B. Hammer	Siemens	X	X		
	Mr. K. Illgner	Aachen University of Technology	X	X		
	Mr. I. Sebestyen	Siemens	X	X		
	Mr. G. Zedler	DBP TELEKOM	X	X	CM	
						
Australia	Mr. M. Biggar	Telecom Australia	X	X	CM	
	Mr. S. Dunstan	Siemens	X	X		
	Mr. T. Sikora	Monash University	X	X		
						
Belgium	Mr. O. Poncin	Belgacom	X	X	CM	
						
Korea 	Mr. J-Y. Nam	ETRI	X	X	CM	
						
USA	Mr. M. Balakrishnan	Philips Labs	X	X		
	Mr. R. Baker	PictureTel	X	-		
	Mr. C-T. Chen	Bellcore	-	X		
	Mr. H. Compter 	RG Associates / Omniphone Technology	X	-		
	Mr. R. Greenblatt 	RG Associates / Omniphone Technology Phone	X	-		
	Mr. R. Grinnell	PictureTel	X	-		
	Mr. B.G. Haskell	AT&T Bell Labs	X	X		
	Mr. D. Hein	VTEL	X	-		
	Mr. D. Klenke	CLI	X	-		
	Mr. J. Liu	Sun Microsystems	X	-		
	Mr. A. Loui	Bellcore	X	-		
	Ms. A. Reibman	AT&T Bell Labs	X	-		
	Mr. R. Schaphorst	DIS	X	X	CM	
	Mr. G. Sullivan	PictureTel	X	-		
	Mr. A. Tabatabai	Tektronix	X	X	CM	
	Mr. M. Uz	David Sarnoff	X	X		
	Ms. J. Vollbrecht	Hughes Aircraft	X	X		
	Ms. M. Yong	Motorola Codex	X	-		
	Mr. Z. Yuan	PictureTel	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. Asai	Mitsubishi	X	X		
	Mr. S. Nogaki	NEC	X	X		
	Mr. S. Okubo	NTT	X	X	Chairman	
	Mr. T. Tanaka	NTT	X		CM	
	Mr. H. Ueno	Toshiba	X	X		
						
Netherlands	Mr. A. Koster	PTT Research	-	X		
	Mr. K. Rijkse	PTT Research	X	-		
	Mr. D. Schinkel	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		
						
Sweden	Ms. C. Verreth	Telia Research 	X	X	CM	

									 CM: Coordinating Member
									(CM): Substitute for CM