5.12.8Hypothetical reference decoder (HRD) (6 – done) 5.12.8.1Ultra-low-delay HRD (3 – done)
Also see J0255.
JCTVC-J0136 AHG9: Improvement of HRD for sub-picture based operation [K. Kazui, J. Koyama, S. Shimada, A. Nakagawa (Fujitsu)]
This contribution proposes changes to the HRD for sub-picture based operation in the HEVC text specification draft 7.
The proposed changes are:
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A modified definition of removal time when low_delay_hrd_flag is equal to 1 (also discussed in J0306)
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An additional SEI message as a hint of early displaying of decoded pictures
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A modified definition of du_cpb_removal_delay (also discussed in J0541 and J0255)
See notes relating to J0569.
An element of the proposal that was not addressed in J0569 was to improve bit efficiency for sending CPB removal delay values for DUs, by using prediction from the CPB removal delay value of the preceding DU. The number of bits used for the delay delta should be sent in VUI. Decision: Adopted this aspect as described.
The contribution additionally proposed the definition of an additional SEI message. The intent was to define a signalling such that display could begin sooner than would ordinarily be indicated by the HRD DPB output delay – including the possibility to begin to output of part of the picture before the entire picture has been decoded. This aspect of the proposal did not seem fully mature, and it appeared possible that the proposed SEI message would not necessarily need to be included in version 1 of the standard – it would still be possible to enable this functionality later. Further study of this was encouraged.
As an editorial suggestion, it was suggested to change the example time interval for tc to a frame-based example rather than a field coding example. (editorial only). Decision (Ed.): Editor action item.
It was remarked that the semantics of the fixed picture rate flag are not compatible with temporal sub-layering. Y.-K. Wang volunteered to draft a proposed fix. This later became reflected in J0548.
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