Of itu-t sg16 wp3 and iso/iec jtc1/SC29/WG11

5.12High-level syntax and slice structure

5.12.1Adaptation parameter sets and parameter set referencing [done]

JCTVC-I0465 Signalling of quantization matrices in SPS and PPS [M. Zhou (TI)] [late]

There is a concern over potential loss of QM data.

Two alternatives to the current APS scheme were

• 
  Just as in AVC (optional presence in SPS with optional over-ride in PPS – i.e. just remove them from the APS)
  
• 
  Some partial update mechanism for PPS
  

It was discussed whether there is a need for frequent update of QMs.

Decision: Take QMs out of APS and put into SPS/PPS as in AVC.

Suggestion: Also remove DF control parameters from APS. Put them in PPS with optional override in SH (and a flag in the PPS to indicate whether the override is possible in the SH). Decision: Agreed.

At the moment, it does not appear that there is a need for APS partial update.

JCTVC-I0046 APS partial update through conditional replacement [S. Wenger, J. Boyce (Vidyo)]

Specific to APS partial update.

JCTVC-I0061 Simplified APS partial update through referencing [M. Li, P. Wu (ZTE), S. Wenger, J. Boyce (Vidyo), D. Flynn (BBC)]

Specific to APS partial update.

JCTVC-I0081 APS partial update – APS update with one or multiple references [Hendry, B. Jeon (LG)]

Specific to APS partial update.

JCTVC-I0083 Error resilience improvements for APS partial updates [Hendry, B. Jeon (LG)]

Specific to APS partial update.

JCTVC-I0082 APS partial update – APS buffer management [Hendry, B. Jeon (LG)]

Mostly about APS partial update. However, it was suggested that the proposal could apply without partial update.

The contribution proposes an alternative to the current method of constraining the ID value in order to constrain the PS storage capacity for the decoder. In the proposed scheme, there is a model of a limited decoder buffer capacity and a some rule for establishing which subset of the PSs are stored.

The proposal is essentially to provide a form of loss detection.

JCTVC-I0189 On APS referring and updating [N. Ouedraogo, E. Francois (Canon)]

On APS partial update, a priority flag for APS, and random access for APSs.

Closely related to I0082, with a signalling of the validity of the APS in terms of the number of pictures.

Also proposes a priority flag to indicate "droppable" APS, such that when nal_ref_flag = 0 for an APS, it could only be referred to by non-reference pictures.

Alternatively, it was suggested that temporal_id could be used for this, which would be easier for a "middle-box" to use as an association of APSs (or PPSs to) with layers. It was remarked that such a concept was also proposed in I0330. This seemed like the desired behaviour to the group. This provides a better solution than the proposed one.

JCTVC-I0069 APS error resilience and partial updating [M. M. Hannuksela, S. M. Gopalakrishna (Nokia)]

On APS partial update and loss resilience for APSs.

This proposal has a similar concept of loss detection and buffering of APSs as in I0082 and I0189. It was remarked that this is analogous to the maximum POC difference constraint.

It was remarked that such a scheme would have a problem for splicing, as the range in which the APS IDs would fall after the splice point is not under the control of the encoder.

An alternative loss detection suggestion was to send a PS checksum in an SEI message. This would not have the splicing issue. It was remarked that this checksum idea had actually been previously proposed for AVC, but in that case it was thought that since the PSs are relatively small, it did not seem necessary, as they could be repeated. This argument would not be valid for APSs.

Definition of an SEI message could even be done later, and we could define one for AVC SPSs and PPSs as well. That idea seems worth further study.

JCTVC-I0572 Crosscheck for APS Error Resilience and Partial Updating (JCTVC-I0069) [S. Deshpande (Sharp)] [late]
JCTVC-I0338 On parameter sets [Y.-K. Wang, Y. Chen, G. Van der Auwera (Qualcomm), P. Wu (ZTE)]

Proposes "GPS" concept for parameter set cross-referencing for APS partial update and other purposes.

The GPS would contain the GPS ID, the APS ID, the PPS ID, and the SPS ID. The SH would contain only the GPS ID.

The other purposes are:

• 
  Enabling sharing of PPSs with different SPSs (to reduce the number of necessary PPSs)
  
• 
  Reduce the number of bits in the SH.
  

It was remarked that loss of a GPS would be a problem, and that the content of the GPS might need to change frequently (which would make out-of-band signalling undesirable).

For further study.

JCTVC-I0067 On APS reference restriction for random access [A. Minezawa, K. Sugimoto, S. Sekiguchi (Mitsubishi)] [late]

The issue is if APS data is sent before a CRA or IDR is sent and then used after that, and suggests that this should be prohibited.

Decision (Ed.): Just put an informative note in the text to point out the issue (Y.-K. Wang and G. J. Sullivan volunteered to provide the text).

5.12.2Random access [first pass done]

See also the recovery point SEI message proposal I0044, HRD for CRA pictures I0277 and APS reference restriction for CRA pictures I0067.

JCTVC-I0133 POC signalling for CRA picture [B. Choi, J. Kim, J. Park (Samsung)]

(Review chaired by Y.-K. Wang.)

Proposes to signal POC MSB for CRA pictures, in the slice header.

It is sufficient to have relative POC relationship in the decoding process.

The usefulness depends on discussion of proposals for signalling of LTRPs in the SPS (I0076 and I0340).

Revisit after decision on those proposals.

JCTVC-I0275 On Leading Pictures [S. Deshpande, A. Segall (Sharp)]

(Review chaired by Y.-K. Wang.)

This document proposes explicit signaling of leading pictures that follow a CRA picture in decoding order and precede it in output order. A NAL unit type is proposed for slices of leading pictures that follow a CRA picture (LFC). It is asserted that this LFC NAL Unit type can allow a server / network node to easily discard leading pictures when sending a bitstream starting at the corresponding CRA picture. The proposed LFC NAL unit type does not require changes to the decoding process of pictures.

Currently, bitstreams are conforming when the leading pictures are present. However, bitstream may not be conforming when the leading pictures are not present, as the CPB may overflow.

A use case mentioned was seeking in either streaming or local playback, wherein it is easier to check whether a NAL unit belongs to a leading picture of the CRA picture at the new starting point.

The ISO base media file format (ISOBMFF) includes signaling of CRA picture type of random access points and the associated leading pictures. But there may be streaming contents not based on ISOBMFF.

Decision: Adopted.
JCTVC-I0278 Signalling of CRA Pictures [S. Deshpande, L. Kerofsky, A. Segall (Sharp)]

(Review chaired by Y.-K. Wang.)

Proposes using a new NAL unit type (or a flag in the slice header) to indicate whether leading pictures associated with a CRA picture is present.

The use case seems depending on the decision on I0277.

Revisit after discussion of I0277.
JCTVC-I0404 CRA pictures with broken links [G. J. Sullivan (Microsoft)]

(Review chaired by Y.-K. Wang.)

Main idea: :Proposes an indication of a so-called "broken-link" CRA (BLC) picture, even when it is in the middle of the bitstream, the decoding process for leading pictures associated with the starting CRA picture is applied for decoding of the leading pictures for the BLC picture in the bitstream.

Comment: Why not discard the leading pictures when splicing? For "lazy" splicing 

1) To signal the indication use a new NAL unit type for the BLC picture.
Decision: Adopt the above proposal piece(s).
2) A restriction that any particular picture can be a leading picture (or a non-decodable picture) associated with at most one CRA picture.

Decision: Adopt
3) And a BLC picture can activate a new SPS (consequently can change spatial resolution), and other details like inclusion of output_prior_pics_flag – text available?

4) To relax the constraints of IDR picture – such that it can behave like a BLC picture, then we still use the IDR term but with the proposed BLC behavior. no text available on this.

5) To decouple the POC relationship from the decodability for pictures that follow CRA picture and BLC in decoding order and to indicate the decodability of a picture
Revisit (check text).

In a later plenary review, a participant said that the broadcast industry would not be interested in the broken link CRA use.

JCTVC-I0236 TLA picture restriction [R. Sjöberg, J. Samuelsson (Ericsson)]

(Review chaired by Y.-K. Wang.)

Proposes to add a restriction: When the current picture is a TLA picture, there shall be no reference picture included in the reference picture set with temproral_id greater than or equal to the temporal_id of the current picture.
Decision (Ed.): Adopted (this is a text bug fix, not a change of design intent – it corrects the specification of the intended behavior of TLA pictures).