ISO/IEC JTC1/SC29/WG11
MPEG94/332
October 1994

ITU-T Telecommunication Standardization Sector	Document AVC-687
Study Group 15	25 October 1994
Experts Group for Video Coding and Systems 
in ATM and Other Network Environments

Source:	RAPPORTEUR FOR Q.2/15 IN ITU-T SG15 (Sakae OKUBO)	
Title:	COMMENTS ON DRAFT ITU-T REC. H.262 | ISO/IEC 13818-2	
Purpose:	Proposal	

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

This document summarizes the comments on the Draft Recommendation H.262 | ISO/IEC 13818-2 (DIS text dated 10 May 1994) which have been collected from the members of the Experts Group for Video Coding and Systems in ATM and Other Network Environments and the ITU-TSB translator for the French text.  It consists of the following two categories:

	- comments with some possible normative change or clarification (with T numbers)
	- comments requiring only editorial change (with E numbers)

This document, together with the Singapore meeting outcome, is also submitted to the Study Group 15 meeting in February 1995 as part of the approval process.

I	Comments with some possible normative change or clarification

#	Page	Section	Location	Comments	
T1	viii	I.4.2.4	Line 37	Since a priority_breakpoint immediately following the DC coefficient is disallowed, it is appropriate that the sentence "such as headers, motion vectors, DC coefficients" be modified as follows:

"such as headers, motion vectors, DC coefficients, first DCT coefficients"	
T2	25	6.2.1	Line 11	It says that "the most significant bit of a byte.".  Referring to Clause 5.2.1 Page 11 Line 13, it can be  reworded as:

"the first bit of a byte."	
T3	42	6.3.3	Lines 8-11	The value of bit_rate field should be specified concretely in the VBR operation.  Since bit_rate is not used to dimension the T-STD any more, "If the bitstream is a variable bitrate stream, the STD specifications in ISO/IEC 13818-1 supersede the VBV, and the bitrate specified here is used to dimension the transport stream STD (2.4.2 in ITU-T Rec. xxx | ISO/IEC 13818-1), or the program stream STD (2.4.5 in ITU-T Rec. xxx | ISO/IEC 13818-1)." should be modified in one of the following ways:

a)	This text should be deleted. If a VBR VBV is defined as in the next comment, the scope of bit_rate is limited to the video layer and specifically, to the VBV model.

b)	"If the bitstream is a variable bitrate stream, the value of bit_rate is not used by the VBV in the video decoder nor by the STD in the systems decoder, hence can be arbitrary."	
T4	42	6.3.3	Lines 8-11	A VBV for VBR operation should be defined. The purpose of this is to define the meaning of bit rate in the VBR context. A VBV that has the same properties as a leaky bucket is our preferred solution: the leak rate defines the maximum bit rate possible over a long period of time, where long is constrained by the bucket size. The encoding of the VBV delay fields has no benefit and should not be mandatory.	
T5	43
etc.	6.3.5
etc.	Line 7	Since this clause explains the semantic meaning of each field in 'Sequence extension', it should be specified that the extension_start_code_identifier is set to 0001. Therefore the sentence "extension_start_code_identifier--This is an 4-bit integer which identifies the extension." might be modified as follows:

"extension_start_code_identifier --This is the bit string 0001 in binary."

Also for the other extensions,  extension_start_code_identifiers should be specified concretely. 
 
For Sequence display extension (Clause 6.3.6 Page 43 Line 33) 
"extension_start_code_identifier --This is the bit string 0010 in binary."

For Sequence scalable extension (Clause 6.3.7 Page 48 Line 16)
"extension_start_code_identifier --This is the bit string 0101 in binary."

For Picture coding extension (Clause 6.3.10 Page 52 Line 4)
"extension_start_code_identifier --This is the bit string 1000 in binary."

For Quant matrix extension (Clause 6.3.11 Page 55 Line 1)
"extension_start_code_identifier --This is the bit string 0011 in binary."

For Picture display extension (Clause 6.3.12 Page 56 Line 10)
"extension_start_code_identifier --This is the bit string 0111 in binary."

For Picture temporal scalable extension (Clause 6.3.13 Page 57 Line 14)
"extension_start_code_identifier --This is the bit string 1010 in binary."

For Picture spatial scalable extension (Clause 6.3.14 Page 57 Line 27)
"extension_start_code_identifier --This is the bit string 1001 in binary."	
T6	48	6.3.6	Table 6-9	It is suggested to delete "FCC" or refer to an appropriate international standard.	
T7	78	7.6.3.1	Line 35	For clarification, the sentence "motion_code, motion_residual and mv_format are fields recovered from the bitstream." should be modified as follows:

"mv_format is a field recovered from the bitstream using Tables 6-17, 18."	
T8	96	7.7.4	Line 17	It says that "Spatial-only prediction (weight_class == 4) is signaled by different values of macroblock_type (see tables B-5 to B-7)".  However, temporal-only prediction (weight_class == 0) is also signaled by different values of macroblock_type.  Therefore it is desirable that this sentence is written as: 

"Spatial-only prediction (weight_class == 4) and temporal-only prediction (weight_class == 0) are signaled by different values of macroblock_type (see tables B-5 to B-7)."	
T9	126	8.5	Table 8-10	Table 8-10 concerning upper bounds for sampling density is confusing and perhaps not as intended. Our concern is with the values given for frames/sec. Should the main profile main level not allow 60 Hz progressive with 240 lines? Should the main profile high level allow 120 interlaced fields per second? We propose that the table be enlarged so that separate limits are given for progressive scan and for interlaced scan, and that MPEG | ITU-T EG take much care with the values put into this table.	
T10	131	Annex A	Line 17	To clarify the description on the refresh period, it should be rewritten as follows:

"Note that Clause 2.3 Std 1180-1990 "Considerations of Specifying IDCT Mismatch Errors" requires the specification of periodic intra-picture coding in order to control the accumulation of mismatch errors. Every macroblock is required to be refreshed before it is coded 132 times as predictive macroblocks.  A skipped macroblock or a bi-directionally predictive macroblocks is excluded from this counting since it does not lead to the accumulation of mismatch errors.  This requirement is the same as indicated in 1180-1990 for visual telephony according to ITU-T Recommendation H.261."	
T11	150	Annex C	Lines 1-5	In the VBV, replace the unclear text about removing stuffing bytes, 'if they are present', by 'that are present'. The intention is that stuffing bits that are present are removed and any others, which come later, are removed next time. The text should be improved to make this clear.
	
T12	159	D.7.4	Figure D-1	Some descriptions in the figure are wrong.

Lower Encoder             ==> Base Layer Encoder
Lower Decoder             ==> Base Layer Decoder
out lower                      ==> out base layer
Enhancement Encoder  ==> Enhancement Layer Encoder
Enhancement Decoder  ==> Enhancement Layer Decoder
out enhance                  ==> out enhancement layer	
T13	159	D.7.4	Line 26	The expression of "higher layer:base layer-to-enhancement layer" is difficult to understand.  The phrase might be written as "video input/out:base layer-to-enhancement layer".	
T14	163	D.7.4.2	Figure D-5	The following description regarding Figure D-5 should be attached after the clause D.7.4.2.

"Figure D-5 shows temporal demultiplexer and remultiplexer for progressive:interlace-to-interlace temporal scalability."	
T15	173	D.13.1.3.4	Line 5	Since the SCIF is not defined exactly, the description "In telecommunications applications......temporal resolution;" should be modified as follows:

"In some telecommunications applications high degree of error resilience might be achieved with temporal scalability by encoding the base layer using the same spatial resolution but only half the temporal resolution of the source;"	

II	Comments requiring only editorial change

#	Page	Section	Location	Comments	
E1	iii	Foreword	Lines 9-10	"The proposal for Recommendation is accepted if 70% or more of the replies from members indicate approval."  ==> "A proposal for Recommendation is put to the approval procedure if unopposed at the Study Group meeting, and accepted if 70% or more of the replies from members indicate approval."	
E2	iii	Foreword	Lines 22-28	==> (underlines are for consideration, not for printing)
This specification has been approved by the ITU-T and ISO-IEC/JTC1. It was prepared jointly by SC29/WG11, also known as MPEG (Moving Picture Experts Group), and the Experts Group for Video Coding and Systems in ATM and Other Network Environments in the ITU-T SG15.  MPEG was formed in 1988 to establish standards for coding of moving pictures and associated audio for various applications such as digital storage media, distribution and communication.  The ITU-T SG15 Experts Group was formed in 1990 to develop video coding and system standards appropriate for B-ISDN using ATM transport.	
E3	iv	I.2	Line 14	DAB  Digital Audio Broadcasting ==> DSB  Digital Sound Broadcasting	
E4	iv	I.2	Line 15	Broadcast ==> Broadcasting	
E5	vii 	I.4.2	Table I-1	ITU-R-601 ==> SDTV
Standard TV ==> SDTV
High Definition ==> HDTV
4:2:0 High Definition ==> 4:2:0 SDTV/HDTV	
E6	vii 	I.4.2	Table I-2	"CIF/SCIF compatibility or scalability" should be deleted in the "Application" column of progressive(30Hz)-progressive(30Hz) scalability, because SCIF has not reached a formal status.	
E7	11	5.3	Line 26	ISO/IEC-defined extensions ==>
ISO/IEC|ITU-T-defined extensions	
E8	12	5.4 (b)	Line 2	'less then' (<) and 'greater then' ==>
'less than' (<) and 'greater than'	
E9	13	6.1	Line 12	See ITU-T Rec.xxx | ISO ==>
See ITU-T Rec.H.222.0 | ISO	
E10	23	6.1.3	Line 12	However, In the 4:2:0 format ==>
However, in the 4:2:0 format	
E11	23	6.1.3	Line 16	in Figure 6-12. ==> in Figure 6-13.	
E12	25	6.2.1	Line 12	the slice code values for ==> the start code values for	
E13	40	6.3.3	Line 13	The horizontal_size_value is the width ==>
The horizontal_size is the width	
E14	40	6.3.3	Line 20	vertical_size_value is the height ==>
vertical_size is the height	
E15	42	6.3.3	Line 8	VBV specified in annex C. ==>
VBV specified in Annex C.	
E16	42	6.3.3	Lines 10 and 11	ITU-T Rec.xxx ==> ITU-T Rec.H.222.0	
E17	42	6.3.3	Line 14	the value encoded in the bitrate field ==>
the value encoded in the bit_rate field	
E18	42	6.3.3	Line 16	"marker_bit -- this is one bit that ... of start codes." can be deleted since it is already globally described in Section 5.3 (p.11)?	
E19	42	6.3.3	Lines 26, 27, 28, 29	Replace reference to "6.3.7" with "6.3.11" 	
E20	44	6.3.6	Line 2	A period is missing at the end of this line.	
E21	45,
46,
48	6.3.6	Tables 6-7, 6-8, 6-9	ITU-R Recommendation 624-4  ==>
Recommendation ITU-R BT.470	
E22	48	6.3.7	Line 17	It is a semantic restriction that ... ==> 
It is a syntactic restriction that  ...	
E23	50	6.3.8	Line 8	IEC standard for "time code..." ... ==>
IEC standard Publication 461 for "time code ..."	
E24	51	6.3.10	Line 9	at the start of play  ==> at the start of operation	
E25	90	7.7.1	Lines 10, 13	base layer ==> lower layer	
E26	91	7.7.3.1	Line 22	if base and ... ==> if lower and	
E27	92	7.7.3.2	Figure 7-14	lower_layer_prediction_vertical_offset ==> lower_layer_vertical_offset
lower_layer_prediction_horizontal_offset ==> lower_layer_horizontal_offset	
E28	92	7.7.3.2	Line 27	7.7.3.5 ==> 7.7.3.4	
E29	93	7.7.3.3	Line 9	7.7.3.3 to 7.7.3.5 ==> 7.7.3.4 to 7.7.3.6	
E30	94	7.7.3.4	Table 7-19	Filter for first field ==> Filter for top field
Filter for second field ==> Filter for bottom field	
E31	94	7.7.3.4	Line 15	prog_field ==> input_prog_field	
E32	96	7.7.4 	Lines 7-8	the picture scalable extension ==>
the picture spatial scalable extension	
E33	96	7.7.4 	Table 7-20	spatial_temporal_weight  class ==> spatial_temporal_weight_class
For spatial_temporal_weight_code_table_index == 0 ==> 
For spatial_temporal_weight_code_table_index == 00
	
E34	106	7.8.3	Line 43	7.4.4 ==> 7.4.3	
E35	107	7.8.3.5	Line 32	7.4.4 ==> 7.4.3	
E36	122	8.3	Line 12	Table 8-6 ==> 8-8	
E37	123	8.4	Line 7	Table 8-7  ==>  Table 8-9	
E38	123	8.4	Line 8	Table 7-29 ==> Table 7-31	
E39	125	8.4.1	table	This table has no numbering.	
E40	125	8.4.1	table	SNR in the "Scalable mode Enh. layer 1" column ==>  SNR, 4:2:0	
E41	129	8.5	Table 8-14a 	HP  in the <level abbreviation> ==>  HL	
E42	151	C.8	Line 21	Note that his ==> Note that this	
E43	155	D.2.5	Line 21	D.2.5 ==> D.2.4	
E44	155	D.2.5	Line 28	sub_carrier  phase ==> sub_carrier_phase	
E45	158	D.7.2.1	Line 39	to a large extend  ==>  to a large extent	
E46	170
171	D.13.1.1.2
D.13.1.2	Line 13
Line 5	D.12.1.1.3  ==>  D.13.1.1.3	
E47	170	D.13.1.1.3	Line 20	D.12.1.1.2  ==>  D.13.1.1.2	
E48	171	D.13.1.2	Line 13	D.12.1.3  ==>  D.13.1.3	
E49	172	D.13.1.3.1	Line 1	PBP ==> PBP (Priority Break Point)
This is the first time "PBP" appears.