ITU-T Telecommunication Standardization Sector	Document AVC-674R
Study Group 15	22 July 1994
Experts Group for Video Coding and Systems
in ATM and Other Network Environments

Source:	RAPPORTEUR (Sakae OKUBO)	
Title:	REPORT OF THE SIXTEENTH EXPERTS GROUP MEETING IN GRIMSTAD (13-22 July 1994) - Part III	
Purpose:	Report	

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Part I	General (see AVC-673R)
Part II	Sole sessions (see AVC-673R)
Part III	Joint sessions

Part III  Joint sessions in Grimstad

Contents

A. 	Introduction
B. 	REQUIREMENTS sub-group
C. 	VIDEO sub-group
D. 	SYSTEMS sub-group

A. Introduction

The joint sessions with MPEG were held at Sorlandet Hotel and Conference Center during 18-22 July 1994 at the kind invitation of Norwegian Standards Association (NSF).  At the opening session on 22 July, Mr. Knut Lindelien, Manager of NSF, made a welcoming address on behalf of the hosting organization.  

The Experts Group appreciated the support and hospitality of the hosting organization.

A list of documents considered during the joint sessions is attached to this report as Annex 1.  Though the DSM-CC group discussion was not a part of the declared joint sessions, its report is contained as Annex 2 because of its high relevance to the work of Experts Group.

B. REQUIREMENTS sub-group (by Sakae OKUBO)

B.1 Introduction

The Requirements sub-group met four days (Monday, Tuesday Wednesday and Thursday) under chairmanship of Mr. Sakae Okubo.  The summary of the work was as follows:

Monday: 	Available input documents were reviewed briefly and discussion items were identified in a sole session.  A joint session with DSM group was held to discuss the requirements description of DSM-CC extension.

Tuesday: 	In addition to two sole sessions, a joint session with Audio group and a joint session with Systems group were held to discuss the requirement descriptions for the NBC audio coding and Real Time Interface, respectively.

Wednesday:	In addition to a sole session, a joint session with Video group was held to discuss the requirement description for 10-bit video.

Thursday	All of the requirements descriptions and achievements during the week were reviewed in two sole sessions.  Another joint session with Video was also held.

B.2 Documents

Input documents
MPEG94/183	NTR	Increase of frame rate from 30 to 60 Hz in Main Level (ML)	
MPEG94/212	Nakasu et al.	Results of reviewing the tables of permissible layer combinations in high Profile	
MPEG94/214	ITU-T Japan	Necessary provision for applying H.222.0 to the H.32X terminals	
MPEG94/240	Australian NB	Closed captioning and MPEG environment	
MPEG94/262	ITU-T EG	Support of ITU-T Control and Indication signals	

Output documents
WG11 N0741	Requirements Group	Description of requirements for MPEG-2 extensions	
WG11 N0762	Requirements Group	Bitstream restrictions for scalable profiles	

B.3 Requirements description for MPEG-2 extensions

The following extensions of MPEG-2 standards were agreed at the previous meetings:

Part 6	Extension for DSM-CC
Part 7	Extension for Non Backward Compatible audio coding
Part 8	Extension for 10-bit video coding
Part 9	Extension for Real Time Interface for Systems decoders

Based on the joint discussion between Requirements sub-group and relevant sub-groups, requirements description was produced as a single document WG11 N0741.  This has been approved by WG11 and is expected to receive comments from MPEG members as well as members of outside communities for further elaboration.

B.4 Pro-scan signal consideration for ML (MPEG94/183)

Document 183 proposed to extend the frame rate upper bound of the Main Level from 30 to 60 for pro-scan sources within the same upper bounds for luminance sample rate.  The meeting did not identify clear applications and were concerned with the specification change at this stage.  If many decoder implementers can accommodate this extension, however, the meeting was of the opinion that the proposal is useful for making the standard more versatile.

B.5 Closed caption and other frame synchronous signals (MPEG94/240, 214, 262)

Documents 240 addressed closed captioning in broadcasting and Documents 214 and 262 addressed control and indication signals in videoconferencing applications.  Both of these signals are synchronous with the corresponding video frames.  The meeting recognized the need to provide for a mechanism in a harmonized way for various applications.  The mechanism is recognized to be already available in the Systems specifications.

B.6 High Profile parameters (MPEG94/212)

Document 212 presented a material to clarify the allowed combinations of Profile and Levels in a high Profile bitstream.  Considering that we requested members to thoroughly review relevant information in Annex E.2 of Video DIS, the meeting decided to produce a supplementary document to clarify the issue.  Mr. Birch undertook this task; the outcome was submitted as WG11 N0762.

B.7 Recommendations of the sub-group

REQUIREMENTS sub-group recommend that:

1)	 WG11 approve the requirements description for the MPEG-2 extensions regarding DSM-CC, NBC audio coding, 10-bit video and Real Time Interface for the Systems decoder as contained in WG11 N0741, and use it as a means to communicate within MPEG as well as with communities outside of MPEG for its further clarification.

2.)	 WG11 draw attention of the members to the request made at the Paris meeting to review the details of permitted combinations of Profiles and Levels in different layers of High Profile and to the material contained in WG11 N0762 which clarifies the issue.

C. VIDEO sub-group (by Gisle Bjoentegaard)

C.1 Conformance testing

Most of the time was spent on conformance testing.  The work is based on creating and decoding demanding bitstreams (evil bitstreams).  14 such bitstreams have been produced so far.  At this meeting several new bitstreams have been proposed to check more coding elements.

C.2 VBV operation for VBR

There is some concern on the maximum bitrate to the decoder in VBR operation.  In VBR mode the maximum of 15 Mbit/s may increase by 20 % to 18 Mbit/s.  A joint meeting with Systems addressed the issue.  No solution was found at this meeting.  An activity was set up to solve the problem before the November meeting.

C.3 Discussions on changes to the DIS

At this meeting no changes to the DIS could be made.  On the other hand, there are some items that delegates feel should be changed in the transition from DIS to IS.  If such changes shall take place, it must be on request from National Bodies.  This meeting addressed some issues to be prepared for response to national bodies at the next meeting.

C.3.1 Decoder memory size

With 50 Hz sequences, the 3:2 pulldown causes problems concerning memory size.  Normally 16 Mbit decoder memory would be sufficient.  However if 3:2 pulldown is used an additional field memory is needed.  3:2 pulldown should not be needed for 50 Hz but it has turned out that the technique may be used for purposes like 24:25 conversion and editing.  One solution seems to be to disallow repetition of the first field of a B-frame.  The group was positive to this change.

C.3.2 Concatenated sequences

There was some documents and discussion on this item in video as well as in the joint meeting with Systems.  The result seems to be that seamless sequence change will be difficult to obtain because users would probably not restrict themselves to edit points anyway.

C.3.3 Increase of frame rate for progressive sequences.

The ITU-T Document AVC-646 (MPEG94/183) - where it is proposed to increase the frame rate for progressive sequences from 30 to 60 frames/sec - was presented.  There was no negative reaction to the proposal.  Several positive views were expressed.

D. SYSTEMS sub-group (by Stuart DUNSTAN)

D.1	Contributions
The Systems subgroup issues discussed in Grimstad, and the relevant documents, are shown in Table 1.
issue	document number	
RTI	247, WG11 N0741, WG11 N0785	
conformance	246, 258, 281, WG11 N0742	
stream_id	262	
closed captions	240, 267, WG11 N0771	
registration & copyright descriptor	298, 299, WG11 N0776	
PTS/DTS and AU definition	293, 302	
H.32X mode change	214	
editorial comments	230	
timing recovery	253	
multiple VCs	254	
splicing	266	
T-STD	271, 272	
TS application	284, 285, 303	
Table 1.  Systems issues and relevant document numbers from the Grimstad meeting.
Many of the issues raised relate to DIS issues, and hence will not be resolved until the Singapore meeting.  A number of the above documents represent output from the meeting.  A DAT tape of Transport Streams for verification testing was made available at the meeting (MPEG 94/303).
D.2	Real Time Interface
The Real Time Interface (RTI) applies only to the Transport Stream, and allows a relaxation of the tight mathematical timing imposed by the T-STD.  It is a coding interface and does not specify lower layer protocols.  The RTI is required to support many types of existing networks.  It should allow easy construction of network adaptors, and should itself be simple to implement.  The work is documented in the RTI Working Draft WG11/N0785, and the requirements document WG11/N0741.  There are two paths for inclusion of the work in ISO/IEC 13818.  One is as ISO/IEC 13818-9, while the other is as a normative annex in ISO/IEC 13818-1.  The latter requires a request from a National Body to do so.
D.3	Conformance
The Systems part of the conformance working draft WG11 N0742 was composed.  For bitstream conformance a number of tests were written.  Decoder conformance was considered in terms of timing, Program Specific Information, and action of the decoder to the bitstream syntax.  It is anticipated that not all coders will implement all Systems functionality.  A list of basic decoder functions, and optional functions, for each of the Program Stream and Transport Stream was composed.  Further work is required to refine the working draft.
D.4	ITU-T C&I channel
The request from ITU-T SG15 EG for a stream_id value, for purposes of a Control and Indication channel in the Rec. H.32X terminal, was heard.  In Atlanta an ITU-T stream_type was allocated.  A matching stream_id is required.  There appeared to be no objection to this request.

For the issue of mode change in the H.32X terminal, the use of PSM/PSI version number and stream_id was recommended.
D.5	Closed captions
There is currently no consensus upon how closed captions should be carried.  While Systems provides the more flexible solution, the cost of this in the Transport Stream may be high, since a Transport Stream packet may be required to carry just a few bytes.  The video user data solution is more efficient, but is less flexible.  MPEG will not standardise this issue.  A liaison document was sent to ITU-R SG 9, informing them of activities within the Grand Alliance and DVB, and requesting that there be some co-ordination between these three bodies.
D.6	Registration and Copyright descriptors
Descriptions of the intended procedures for the registration and copyright descriptor were composed.  These are contained in  MPEG 94/299 and WG11/N0776, respectively.
D.7	Joint meeting with Video
A joint meeting with the Video subgroup was held to discuss the following issues
D.7.1	Video VBV and the Systems T-STD
There is concern about the interaction of these two timing models, especially in the case of VBR.  The Systems T-STD places a hard limit on the maximum bit rate into the decoder, which is related to the profile and level.  The problem is that Video has no way to describe, or limit, VBR video.  Currently, Video allows Systems to handle all timing in the case of VBR.  The Video DIS says that when present, the Systems STD supersedes the Video part.  This may or may not be also true for CBR.  Input from National Bodies on how to deal with VBR is sought.  An ad-hoc group to consider this issue was established.
D.7.2	seamless operation
In Video a change of bit rate, picture resolution, or frame rate requires a new sequence to begin.  The problem is how to maintain buffer management, and a glitch free display, during a sequence change.  Currently Video says nothing about what happens between a Sequence End Code and a Sequence Header.  An informative annex may be added, if requested by National Bodies.
D.7.3	trick modes
There is some question as to how trick modes should be tested in the compliance specification, since trick modes imply the use of a display.  The display, however, is outside of the Systems and Video standards.
D.8	Joint meeting with DSM-CC
The DSM-CC subgroup reported to the Systems subgroup upon their activities.  DSM-CC requested that reference to elementary streams be allowed within DSM-CC.  The Systems subgroup approved this.  The DSM-CC subgroup are considering ITU-T C&I channel requirements.  DSM-CC are considering using Remote Procedure Call (RPC) and ITU-T Rec. X.500 protocols.  The following documents were relevant to the DSM-CC subgroup: MPEG 94/191, 213, 216, 217, 234, 262, 273, 274, 276, 288.  A DSM-CC working draft is required at the Singapore meeting.  In Grimstad, a preliminary DSM-CC working draft was produced (WG11/N0744).
D.9	PTS/DTS and Access Unit definition
A change to the DIS in Atlanta brought about inconsistencies in the DIS with respect to PTS/DTSs and what they refer to in the video structure: do they refer to sequence, GOP, or picture start codes?  MPEG-1 appears to be also inconsistent.  The issue is not yet resolved.
D.10	Ad-hoc groups
The following ad hoc groups were formed:
•	ad-hoc group on Conformance Testing - chairman, Jan van de Meer (one meeting planned)
•	ad-hoc group on real-time interface - chairman, Joel Zdepski
•	ad-hoc group on relation between VBV and STD models - chairman, John Morris

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