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

6.4.7.3Proposals on multi-layer HRD / ultra-low-delay HRD

The current draft treats all of the bitstream for an operation point as a single CPB.

A "partitioned CPB" would have separate CPB flows for the contents of each partition.

As proposed by Sony, each layer in a layer set would be a separate partition.

Nokia proposes the additional flexibility of grouping multiple layers into a single partition.

In the RTP context, there is a concept of multi-session transmission (MST).

In the MPEG-2 context, there is a buffer flow model for each stream.

Initally agreed plan: Establish level constraints based on the combined HRD parameters of a layer set. Encoder can optionally choose to send partition-specific HRD parameters. Partitions can be individual layers or groups of layers.

Multi-layer CPB O0164 and O0234 proponents were coordinating offline to produce text.

Further discussed Wed joint 3V+VC (GJS & JRO).

Result, with additional co-authorship added, was presented as O0164-v2.

Version 2 of the contribution modifies the proposed specification text to enable specifying HRD parameters per layer sets.

For sequence-level HRD parameter signalling two versions of the signalling are included:

• 
  Signalling of sequence-level HRD parameters in VPS VUI (included in file “JCTVC-O0164_JCT3V-F0059 spectext-v2 VPS_VUI_signalling.doc”).
  
• 
  Signalling of sequence-level HRD parameters in the bitstream partition HRD SEI message (included in file “JCTVC-O0164_JCT3V-F0059 spectext-v2 SEI_signalling.doc”). It is asserted that this option could make the addition of layers in redistribution points easier, as VPS rewriting may be avoided.
  

Either or both of the signalling options were proposed.

Decision: Adopt, modified as follows.

• 
  It was suggested to constrain the stalling based on the relative cpb removal times, which must be in decoding order. The "du_based_bpb_sync_flag" is not needed, in view of this.
  
• 
  SEI in the highest layer of the layer set or (inclusive "or") VPS VUI is used to carry the parameters (at encoder discretion).
  
• 
  SEI in higher layer and SEI in VUI do not need to repeat information available in some lower layer.
  
• 
  Shall be after APS SEI and buffering period SEI and before all other SEI of all layers except other HRD related SEI.
  

Further study encouraged on potentially creating a new nesting message type rather than putting one nesting within another.
JCTVC-O0164 MV-HEVC/SHVC HLS / JCT-VC AHG20: Multi-layer HRD operation [M. M. Hannuksela (Nokia), S. Hattori, K. Sato, T. Suzuki, A. Tabatabai (Sony), S. Narasimhan, A. Luthra (Arris)]

See notes above in this section of the report.