5.12.2.2Splicing and editing (2 – done)
JCTVC-J0108 AHG9: Splicing-friendly coding of some parameters [Y.-K. Wang, Y. Chen (Qualcomm)]
During splicing, two bitstreams may refer to few parameter sets with the same ID for each type of parameter sets but with different content. This document proposes that all parameter set IDs are fixed-length coded, and placed before any entropy-coded syntax elements in each parameter set or coded slice NAL unit. Furthermore, it is proposed that the syntax element no_output_of_prior_pics_flag and the syntax element rap_pic_id are placed before any entropy-coded syntax elements in the slice header, and the syntax element rap_pic_id is fixed-length coded. It is asserted that the changes enable lightweight splicing of bitstreams.
A cross-check is in J0501.
It was remarked that this has implications for extensibility, as fixed-length coding restricts the number of possible values that can be supported. It also affects coding efficiency, as it may sometimes use more bits than would be required for VLC coding.
An aspect relating to mandating a value for no_output_of_prior_pics_flag needs further discussion. No action on that aspect.
It was noted that this proposal interacts with the proposal to create a slice header parameter set.
Regarding moving the rap_pic_id and no_output_of_prior_pics_flag before VLC data
It was suggested not to allow the value 0 for the rap_pic_id.
It was asked whether we actually still need rap_pic_id. Decision: Drop rap_pic_id.
Regarding the no_output_of_prior_pics_flag before VLC data – Decision: Move it.
Various potential alternative approaches were discussed for the parameter set ID aspects, especially in the slice header. Further study was encouraged about that.
It was remarked that the draft is missing the condition that first_slice_in_pic_flag = 1 for testing for the first VCL NAL unit. Decision (Ed.): It was agreed that this should be fixed.
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